6.5: The Overall Impact of Climate Change - Biology

6.5:  The Overall Impact of Climate Change - Biology

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6.5: The Overall Impact of Climate Change

Global Climate Change Impacts in the United States 2009 Report Legacy site

800,000 Year record of CO2 Concentration Analysis of air bubbles trapped in an Antarctic ice core extending back 800,000 years documents the Earth’s changing carbon dioxide concentration. Over this long period, natural factors have caused the atmospheric carbon dioxide concentration to vary within a range of about 170 to 300 parts per million (ppm). Temperature-related data make clear that these variations have played a central role in determining the global climate. As a result of human activities, the present carbon dioxide concentration of about 385 ppm is about 30 percent above its highest level over at least the last 800,000 years. In the absence of strong control measures, emissions projected for this century would result in the carbon dioxide concentration increasing to a level that is roughly 2 to 3 times the highest level occurring over the glacial-interglacial era that spans the last 800,000 or more years. Image References: Luthi et al. Tans IIASA1 This introduction to global climate change explains very briefly what has been happening to the world’s climate and why, and what is projected to happen in the future. While this report focuses on climate change impacts in the United States, understanding these changes and their impacts requires an understanding of the global climate system.

Many changes have been observed in global climate over the past century. The nature and causes of these changes have been comprehensively chronicled in a variety of recent reports, such as those by the Intergovernmental Panel on Climate Change (IPCC) and the U.S. Climate Change Science Program (CCSP). This section does not intend to duplicate these comprehensive efforts, but rather to provide a brief synthesis, and to integrate more recent work with the assessments of the IPCC, CCSP, and others.

Influences on Climate

Human activities have led to large increases in heat-trapping gases over the past century.

2000 Years of Greenhouse Gas Concentrations Increases in concentrations of these gases since 1750 are due to human activities in the industrial era. Concentration units are parts per million (ppm) or parts per billion (ppb), indicating the number of molecules of the greenhouse gas per million or billion molecules of air. Image References: Forster et al.2 Blasing3

The Earth’s climate depends on the functioning of a natural “greenhouse effect.” This effect is the result of heat-trapping gases (also known as greenhouse gases) like water vapor, carbon dioxide, ozone, methane, and nitrous oxide, which absorb heat radiated from the Earth’s surface and lower atmosphere and then radiate much of the energy back toward the surface. Without this natural greenhouse effect, the average surface temperature of the Earth would be about 60°F colder. However, human activities have been releasing additional heat-trapping gases, intensifying the natural greenhouse effect, thereby changing the Earth’s climate.

Climate is influenced by a variety of factors, both human-induced and natural. The increase in the carbon dioxide concentration has been the principal factor causing warming over the past 50 years. Its concentration has been building up in the Earth’s atmosphere since the beginning of the industrial era in the mid-1700s, primarily due to the burning of fossil fuels (coal, oil, and natural gas) and the clearing of forests. Human activities have also increased the emissions of other greenhouse gases, such as methane, nitrous oxide, and halocarbons.2 These emissions are thickening the blanket of heat-trapping gases in Earth’s atmosphere, causing surface temperatures to rise.

Heat-trapping gases

Carbon dioxide concentration has increased due to the use of fossil fuels in electricity generation, transportation, and industrial and household uses. It is also produced as a by-product during the manufacturing of cement. Deforestation provides a source of carbon dioxide and reduces its uptake by trees and other plants. Globally, over the past several decades, about 80 percent of human-induced carbon dioxide emissions came from the burning of fossil fuels, while about 20 percent resulted from deforestation and associated agricultural practices. The concentration of carbon dioxide in the atmosphere has increased by roughly 35 percent since the start of the industrial revolution.2

Methane concentration has increased mainly as a result of agriculture raising livestock (which produce methane in their digestive tracts) mining, transportation, and use of certain fossil fuels sewage and decomposing garbage in landfills. About 70 percent of the emissions of atmospheric methane are now related to human activities.4

Nitrous oxide concentration is increasing as a result of fertilizer use and fossil fuel burning.

Halocarbon emissions come from the release of certain manufactured chemicals to the atmosphere. Examples include chlorofluorocarbons (CFCs), which were used extensively in refrigeration and for other industrial processes before their presence in the atmosphere was found to cause stratospheric ozone depletion. The abundance of these gases in the atmosphere is now decreasing as a result of international regulations designed to protect the ozone layer. Continued decreases in ozone-depleting halocarbon emissions are expected to reduce their relative influence on climate change in the future.2,5 Many halocarbon replacements, however, are potent greenhouse gases, and their concentrations are increasing.6

Ozone is a greenhouse gas, and is continually produced and destroyed in the atmosphere by chemical reactions. In the troposphere, the lowest 5 to 10 miles of the atmosphere near the surface, human activities have increased the ozone concentration through the release of gases such as carbon monoxide, hydrocarbons, and nitrogen oxides. These gases undergo chemical reactions to produce ozone in the presence of sunlight. In addition to trapping heat, excess ozone in the troposphere causes respiratory illnesses and other human health problems.

In the stratosphere, the layer above the troposphere, ozone exists naturally and protects life on Earth from exposure to excessive ultraviolet radiation from the Sun. As mentioned previously, halocarbons released by human activities destroy ozone in the stratosphere and have caused the ozone hole over Antarctica.7 Changes in the stratospheric ozone layer have contributed to changes in wind patterns and regional climates in Antarctica.8

Water vapor is the most important and abundant greenhouse gas in the atmosphere. Human activities produce only a very small increase in water vapor through irrigation and combustion processes.2 However, the surface warming caused by human-produced increases in other greenhouse gases leads to an increase in atmospheric water vapor, since a warmer climate increases evaporation and allows the atmosphere to hold more moisture. This creates an amplifying “feedback loop,” leading to more warming.

Other human influences

Major Warming and Cooling Influences on Climate The figure above shows the amount of warming influence (red bars) or cooling influence (blue bars) that different factors have had on Earth’s climate over the industrial age (from about 1750 to the present). Results are in watts per square meter. The longer the bar, the greater the influence on climate. The top part of the box includes all the major human-induced factors, while the second part of the box includes the Sun, the only major natural factor with a long-term effect on climate. The cooling effect of individual volcanoes is also natural, but is relatively short-lived (2 to 3 years), thus their influence is not included in this figure. The bottom part of the box shows that the total net effect (warming influences minus cooling influences) of human activities is a strong warming influence. The thin lines on each bar provide an estimate of the range of uncertainty. Image Reference: Forster et al.2 In addition to the global-scale climate effects of heat-trapping gases, human activities also produce additional local and regional effects. Some of these activities partially offset the warming caused by greenhouse gases, while others increase the warming. One such influence on climate is caused by tiny particles called “aerosols” (not to be confused with aerosol spray cans). For example, the burning of coal produces emissions of sulfur-containing compounds. These compounds form “sulfate aerosol” particles, which reflect some of the incoming sunlight away from the Earth, causing a cooling influence at the surface. Sulfate aerosols also tend to make clouds more efficient at reflecting sunlight, causing an additional indirect cooling effect. Another type of aerosol, often referred to as soot or black carbon, absorbs incoming sunlight and traps heat in the atmosphere. Thus, depending on their type, aerosols can either mask or increase the warming caused by increased levels of greenhouse gases.9 On a globally averaged basis, the sum of these aerosol effects offsets some of the warming caused by heat-trapping gases.10

The effects of various greenhouse gases and aerosol particles on Earth’s climate depend in part on how long these gases and particles remain in the atmosphere. After emission, the atmospheric concentration of carbon dioxide remains elevated for thousands of years, and that of methane for decades, while the elevated concentrations of aerosols only persist for days to weeks.11,12 The climate effects of reductions in emissions of carbon dioxide and other long-lived gases do not become apparent for at least several decades. In contrast, reductions in emissions of short-lived compounds can have a rapid, but complex effect since the geographic patterns of their climatic influence and the resulting surface temperature responses are quite different. One modeling study found that while the greatest emissions of short-lived pollutants in summertime by late this century are projected to come from Asia, the strongest climate response is projected to be over the central United States.9

Human activities have also changed the land surface in ways that alter how much heat is reflected or absorbed by the surface. Such changes include the cutting and burning of forests, the replacement of other areas of natural vegetation with agriculture and cities, and large-scale irrigation. These transformations of the land surface can cause local (and even regional) warming or cooling. Globally, the net effect of these changes has probably been a slight cooling of the Earth’s surface over the past 100 years.13,14

Natural influences

Two important natural factors also influence climate: the Sun and volcanic eruptions. Over the past three decades, human influences on climate have become increasingly obvious, and global temperatures have risen sharply. During the same period, the Sun’s energy output (as measured by satellites since 1979) has followed its historical 11-year cycle of small ups and downs, but with no net increase (see Measurements of Surface Temperature and Sun's Energy figure below).15 The two major volcanic eruptions of the past 30 years have had short-term cooling effects on climate, lasting 2 to 3 years.16 Thus, these natural factors cannot explain the warming of recent decades in fact, their net effect on climate has probably been a slight cooling influence over this period. Slow changes in Earth’s orbit around the Sun and its tilt toward or away from the Sun are also a purely natural influence on climate, but are only important on timescales from thousands to many tens of thousands of years.

The climate changes that have occurred over the last century are not solely caused by the human and natural factors described above. In addition to these influences, there are also fluctuations in climate that occur even in the absence of changes in human activities, the Sun, or volcanoes. One example is the El Niño phenomenon, which has important influences on many aspects of regional and global climate. Many other modes of variability have been identified by climate scientists and their effects on climate occur at the same time as the effects of human activities, the Sun, and volcanoes.

Carbon release and uptake

Once carbon dioxide is emitted to the atmosphere, some of it is absorbed by the oceans and taken up by vegetation, although this storage may be temporary. About 45 percent of the carbon dioxide emitted by human activities in the last 50 years is now stored in the oceans and vegetation. The rest has remained in the air, increasing the atmospheric concentration.1,2,17 It is thus important to understand not only how much carbon dioxide is emitted, but also how much is taken up, over what time scales, and how these sources and “sinks” of carbon dioxide might change as climate continues to warm. For example, it is known from long records of Earth’s climate history that under warmer conditions, carbon tends to be released, for instance, from thawing permafrost, initiating a feedback loop in which more carbon release leads to more warming which leads to further release, and so on.18,19

Global emissions of carbon dioxide have been accelerating. The growth rate increased from 1.3 percent per year in the 1990s to 3.3 percent per year between 2000 and 2006.20 The increasing emissions of carbon dioxide are the primary cause of the increased concentration of carbon dioxide observed in the atmosphere. There is also evidence that a smaller fraction of the annual human-induced emissions is now being taken up than in the past, leading to a greater fraction remaining in the atmosphere and an accelerating rate of increase in the carbon dioxide concentration.20

Ocean acidification

As the ocean absorbs carbon dioxide from the atmosphere, seawater is becoming less alkaline (its pH is decreasing) through a process generally referred to as ocean acidification. The pH of seawater has decreased significantly since 1750,21,22 and is projected to drop much more dramatically by the end of the century if carbon dioxide concentrations continue to increase.23 Such ocean acidification is essentially irreversible over a time scale of centuries. As discussed in the Ecosystems sector and Coasts region, ocean acidification affects the process of calcification by which living things create shells and skeletons, with substantial negative consequences for coral reefs, mollusks, and some plankton species important to ocean food chains.24

Observed Climate Change

Global average temperature and sea level have increased, and precipitation patterns have changed

Temperatures are rising

Global Temperature and Carbon Dioxide Global annual average temperature (as measured over both land and oceans). Red bars indicate temperatures above and blue bars indicate temperatures below the average temperature for the period 1901-2000. The black line shows atmospheric carbon dioxide (CO2) concentration in parts per million (ppm). While there is a clear long-term global warming trend, each individual year does not show a temperature increase relative to the previous year, and some years show greater changes than others.25 These year-to-year fluctuations in temperature are due to natural processes, such as the effects of El Niños, La Niñas, and the eruption of large volcanoes. Image Reference: NOAA/NCDC26 Global average surface air temperature has increased substantially since 1970.27 The estimated change in the average temperature of Earth’s surface is based on measurements from thousands of weather stations, ships, and buoys around the world, as well as from satellites. These measurements are independently compiled, analyzed, and processed by different research groups. There are a number of important steps in the data processing. These include identifying and adjusting for the effects of changes in the instruments used to measure temperature, the measurement times and locations, the local environment around the measuring site, and such factors as satellite orbital drift. For instance, the growth of cities can cause localized “urban heat island” effects.

A number of research groups around the world have produced estimates of global-scale changes in surface temperature. The warming trend that is apparent in all of these temperature records is confirmed by other independent observations, such as the melting of Arctic sea ice, the retreat of mountain glaciers on every continent,28 reductions in the extent of snow cover, earlier blooming of plants in spring, and increased melting of the Greenland and Antarctic ice sheets.29,30 Because snow and ice reflect the Sun’s heat, this melting causes more heat to be absorbed, which causes more melting, resulting in another feedback loop.19

Additionally, temperature measurements above the surface have been made by weather balloons since the late 1940s, and from satellites since 1979. These measurements show warming of the troposphere, consistent with the surface warming.31,32 They also reveal cooling in the stratosphere.31 This pattern of tropospheric warming and stratospheric cooling agrees with our understanding of how atmospheric temperature would be expected to change in response to increasing greenhouse gas concentrations and the observed depletion of stratospheric ozone.13

Precipitation patterns are changing

Precipitation is not distributed evenly over the globe. Its average distribution is governed primarily by atmospheric circulation patterns, the availability of moisture, and surface terrain effects. The first two of these factors are influenced by temperature. Thus, human-caused changes in temperature are expected to alter precipitation patterns.

Observations show that such shifts are occurring. Changes have been observed in the amount, intensity, frequency, and type of precipitation. Pronounced increases in precipitation over the past 100 years have been observed in eastern North America, southern South America, and northern Europe. Decreases have been seen in the Mediterranean, most of Africa, and southern Asia. Changes in the geographical distribution of droughts and flooding have been complex. In some regions, there have been increases in the occurrences of both droughts and floods.29 As the world warms, northern regions and mountainous areas are experiencing more precipitation falling as rain rather than snow.33 Widespread increases in heavy precipitation events have occurred, even in places where total rain amounts have decreased. These changes are associated with the fact that warmer air holds more water vapor evaporating from the world’s oceans and land surface.32 This increase in atmospheric water vapor has been observed from satellites, and is primarily due to human influences.34,35

Sea level is rising

After at least 2,000 years of little change, sea level rose by roughly 8 inches over the past century. Satellite data available over the past 15 years show sea level rising at a rate roughly double the rate observed over the past century.36

There are two principal ways in which global warming causes sea level to rise. First, ocean water expands as it warms, and therefore takes up more space. Warming has been observed in each of the world’s major ocean basins, and has been directly linked to human influences.37,38

Cumulative Decrease in Global Glacier Ice As temperatures have risen, glaciers around the world have shrunk. The graph shows the cumulative decline in glacier ice worldwide. Image Reference: Meier et al.28 Second, warming leads to the melting of glaciers and ice sheets, which raises sea level by adding water to the oceans. Glaciers have been retreating worldwide for at least the last century, and the rate of retreat has increased in the past decade.30,39 Only a few glaciers are actually advancing (in locations that were well below freezing, and where increased precipitation has outpaced melting). The total volume of glaciers on Earth is declining sharply. The progressive disappearance of glaciers has implications not only for the rise in global sea level, but also for water supplies in certain densely populated regions of Asia and South America.

The Earth has major ice sheets on Greenland and Antarctica. These ice sheets are currently losing ice volume by increased melting and calving of icebergs, contributing to sea-level rise. The Greenland Ice Sheet has also been experiencing record amounts of surface melting, and a large increase in the rate of mass loss in the past decade.40 If the entire Greenland Ice Sheet melted, it would raise sea level by about 20 feet. The Antarctic Ice Sheet consists of two portions, the West Antarctic Ice Sheet and the East Antarctic Ice Sheet. The West Antarctic Ice Sheet, the more vulnerable to melting of the two, contains enough water to raise global sea levels by about 16 to 20 feet.30 If the East Antarctic Ice Sheet melted entirely, it would raise global sea level by about 200 feet. Complete melting of these ice sheets over this century or the next is thought to be virtually impossible, although past climate records provide precedent for very significant decreases in ice volume, and therefore increases in sea level.41,42

Human "Fingerprint" on Climate

The global warming of the past 50 years is due primarily to human-induced increases in heat-trapping gases. Human “fingerprints” also have been identified in many other aspects of the climate system, including changes in ocean heat content, precipitation, atmospheric moisture, and Arctic sea ice.

In 1996, the IPCC Second Assessment Report43 cautiously concluded that “the balance of evidence suggests a discernible human influence on global climate.” Since then, a number of national and international assessments have come to much stronger conclusions about the reality of human effects on climate. Recent scientific assessments find that most of the warming of the Earth’s surface over the past 50 years has been caused by human activities.44,45

This conclusion rests on multiple lines of evidence. Like the warming “signal” that has gradually emerged from the “noise” of natural climate variability, the scientific evidence for a human influence on global climate has accumulated over the past several decades, from many hundreds of studies. No single study is a “smoking gun.” Nor has any single study or combination of studies undermined the large body of evidence supporting the conclusion that human activity is the primary driver of recent warming.

The first line of evidence is our basic physical understanding of how greenhouse gases trap heat, how the climate system responds to increases in greenhouse gases, and how other human and natural factors influence climate. The second line of evidence is from indirect estimates of climate changes over the last 1,000 to 2,000 years. These records are obtained from living things and their remains (like tree rings and corals) and from physical quantities (like the ratio between lighter and heavier isotopes of oxygen in ice cores) which change in measurable ways as climate changes. The lesson from these data is that global surface temperatures over the last several decades are clearly unusual, in that they were higher than at any time during at least the past 400 years.46 For the Northern Hemisphere, the recent temperature rise is clearly unusual in at least the last 1,000 years.46,47

The third line of evidence is based on the broad, qualitative consistency between observed changes in climate and the computer model simulations of how climate would be expected to change in response to human activities. For example, when climate models are run with historical increases in greenhouse gases, they show gradual warming of the Earth and ocean surface, increases in ocean heat content and the temperature of the lower atmosphere, a rise in global sea level, retreat of sea ice and snow cover, cooling of the stratosphere, an increase in the amount of atmospheric water vapor, and changes in large-scale precipitation and pressure patterns. These and other aspects of modeled climate change are in agreement with observations.13,48

Finally, there is extensive statistical evidence from so-called “fingerprint” studies. Each factor that affects climate produces a unique pattern of climate response, much as each person has a unique fingerprint. Fingerprint studies exploit these unique signatures, and allow detailed comparisons of modeled and observed climate change patterns.43 Scientists rely on such studies to attribute observed changes in climate to a particular cause or set of causes. In the real world, the climate changes that have occurred since the start of the Industrial Revolution are due to a complex mixture of human and natural causes. The importance of each individual influence in this mixture changes over time. Of course, there are not multiple Earths, which would allow an experimenter to change one factor at a time on each Earth, thus helping to isolate different fingerprints. Therefore, climate models are used to study how individual factors affect climate. For example, a single factor (like greenhouse gases) or a set of factors can be varied, and the response of the modeled climate system to these individual or combined changes can thus be studied.49

Separating Human and Natural Influences on Climate The blue band shows how global average temperatures would have changed due to natural forces only, as simulated by climate models. The red band shows model projections of the effects of human and natural forces combined. The black line shows actual observed global average temperatures. As the blue band indicates, without human influences, temperature over the past century would actually have first warmed and then cooled slightly over recent decades.50 Image Reference: Hegerl et al.48 For example, when climate model simulations of the last century include all of the major influences on climate, both human-induced and natural, they can reproduce many important features of observed climate change patterns. When human influences are removed from the model experiments, results suggest that the surface of the Earth would actually have cooled slightly over the last 50 years. The clear message from fingerprint studies is that the observed warming over the last half-century cannot be explained by natural factors, and is instead caused primarily by human factors.13,49

Another fingerprint of human effects on climate has been identified by looking at a slice through the layers of the atmosphere, and studying the pattern of temperature changes from the surface up through the stratosphere. In all climate models, increases in carbon dioxide cause warming at the surface and in the troposphere, but lead to cooling of the stratosphere. For straightforward physical reasons, models also calculate that the human-caused depletion of stratospheric ozone has had a strong cooling effect in the stratosphere. There is a good match between the model fingerprint in response to combined carbon dioxide and ozone changes and the observed pattern of tropospheric warming and stratospheric cooling (see Patterns of Temperature Change figure below).13

Measurements of Surface Temperature and Sun’s Energy The Sun’s energy received at the top of Earth’s atmosphere has been measured by satellites since 1978. It has followed its natural 11-year cycle of small ups and downs, but with no net increase (bottom). Over the same period, global temperature has risen markedly (top).51 Image References: NOAA/NCDC Frolich and Lean Willson and Mordvinov Dewitte et al.52

In contrast, if most of the observed temperature change had been due to an increase in solar output rather than an increase in greenhouse gases, Earth’s atmosphere would have warmed throughout its full vertical extent, including the stratosphere.8 The observed pattern of atmospheric temperature changes, with its pronounced cooling in the stratosphere, is therefore inconsistent with the hypothesis that changes in the Sun can explain the warming of recent decades. Moreover, direct satellite measurements of solar output show slight decreases during the recent period of warming.

The earliest fingerprint work53 focused on changes in surface and atmospheric temperature. Scientists then applied fingerprint methods to a whole range of climate variables,49,54 identifying human-caused climate signals in the heat content of the oceans,37,38 the height of the tropopause55 (the boundary between the troposphere and stratosphere, which has shifted upward by hundreds of feet in recent decades), the geographical patterns of precipitation,56 drought,57 surface pressure,58 and the runoff from major river basins.59

Studies published after the appearance of the IPCC Fourth Assessment Report in 2007 have also found human fingerprints in the increased levels of atmospheric moisture34,35 (both close to the surface and over the full extent of the atmosphere), in the decline of Arctic sea ice extent,60 and in the patterns of changes in Arctic and Antarctic surface temperatures.61

The message from this entire body of work is that the climate system is telling a consistent story of increasingly dominant human influence – the changes in temperature, ice extent, moisture, and circulation patterns fit together in a physically consistent way, like pieces in a complex puzzle.

Increasingly, this type of fingerprint work is shifting its emphasis. As noted, clear and compelling scientific evidence supports the case for a pronounced human influence on global climate. Much of the recent attention is now on climate changes at continental and regional scales,62,63 and on variables that can have large impacts on societies. For example, scientists have established causal links between human activities and the changes in snowpack, maximum and minimum temperature, and the seasonal timing of runoff over mountainous regions of the western United States.33 Human activity is likely to have made a substantial contribution to ocean surface temperature changes in hurricane formation regions.64,65,66 Researchers are also looking beyond the physical climate system, and are beginning to tie changes in the distribution and seasonal behavior of plant and animal species to human-caused changes in temperature and precipitation.67,68

Patterns of Temperature Change Produced by Various Atmospheric Factors, 1958-1999 Climate simulations of the vertical profile of temperature change due to various factors, and the effect due to all factors taken together. The panels above represent a cross-section of the atmosphere from the north pole to the south pole, and from the surface up into the stratosphere. The black lines show the location of the tropopause, the boundary between the lower atmosphere (troposphere) and the stratosphere. Image Source: Modified from CCSP SAP 1.169 For over a decade, one aspect of the climate change story seemed to show a significant difference between models and observations.13 In the tropics, all models predicted that with a rise in greenhouse gases, the troposphere would be expected to warm more rapidly than the surface. Observations from weather balloons, satellites, and surface thermometers seemed to show the opposite behavior (more rapid warming of the surface than the troposphere). This issue was a stumbling block in our understanding of the causes of climate change. It is now largely resolved.70 Research showed that there were large uncertainties in the satellite and weather balloon data. When uncertainties in models and observations are properly accounted for, newer observational data sets (with better treatment of known problems) are in agreement with climate model results.32,71,72,73,74

This does not mean, however, that all remaining differences between models and observations have been resolved. The observed changes in some climate variables, such as Arctic sea ice,60,75 some aspects of precipitation,56,76 and patterns of surface pressure,58 appear to be proceeding much more rapidly than models have projected. The reasons for these differences are not well understood. Nevertheless, the bottom-line conclusion from climate fingerprinting is that most of the observed changes studied to date are consistent with each other, and are also consistent with our scientific understanding of how the climate system would be expected to respond to the increase in heat-trapping gases resulting from human activities.13,48

Scientists are sometimes asked whether extreme weather events can be linked to human activities.23 Scientific research has concluded that human influences on climate are indeed changing the likelihood of certain types of extreme events. For example, an analysis of the European summer heat wave of 2003 found that the risk of such a heat wave is now roughly four times greater than it would have been in the absence of human-induced climate change.66,77

Like fingerprint work, such analyses of human-caused changes in the risks of extreme events rely on information from climate models, and on our understanding of the physics of the climate system. All of the models used in this work have imperfections in their representation of the complexities of the “real world” climate system.78,79 These are due to both limits in our understanding of the climate system, and in our ability to represent its complex behavior with available computer resources. Despite this, models are extremely useful, for a number of reasons.

First, despite remaining imperfections, the current generation of climate models accurately portrays many important aspects of today’s weather patterns and climate.78,79 Models are constantly being improved, and are routinely tested against many observations of Earth’s climate system. Second, the fingerprint work shows that models capture not only our present-day climate, but also key features of the observed climate changes over the past century.46 Third, many of the large-scale observed climate changes (such as the warming of the surface and troposphere, and the increase in the amount of moisture in the atmosphere) are driven by very basic physics, which is well-represented in models.34 Fourth, climate models can be used to predict changes in climate that can be verified in the real world. Examples include the short-term global cooling subsequent to the eruption of Mount Pinatubo and the stratospheric cooling with increasing carbon dioxide. Finally, models are the only tools that exist for trying to understand the climate changes likely to be experienced over the course of this century. No period in Earth’s geological history provides an exact analogue for the climate conditions that will unfold in the coming decades.19

Projected Climate Change

Global temperatures are projected to continue to rise over this century by how much and for how long depends on a number of factors, including the amount of heat-trapping gas emissions and how sensitive the climate is to those emissions.

Some continued warming of the planet is projected over the next few decades due to past emissions. Choices made now will influence the amount of future warming. Lower levels of heat-trapping emissions will yield less future warming, while higher levels will result in more warming, and more severe impacts on society and the natural world.

Emissions scenarios

The IPCC developed a set of scenarios in a Special Report on Emissions Scenarios (SRES).80 These have been extensively used to explore the potential for future climate change. None of these scenarios, not even the one called “lower”, includes implementation of policies to limit climate change or to stabilize atmospheric concentrations of heat-trapping gases. Rather, differences among these scenarios are due to different assumptions about changes in population, rate of adoption of new technologies, economic growth, and other factors.

The IPCC emission scenarios also do not encompass the full range of possible futures: emissions can change less than those scenarios imply, or they can change more. Recent carbon dioxide emissions are, in fact, above the highest emissions scenario developed by the IPCC81 (see figure below). Whether this will continue is uncertain.

There are also lower possible emissions paths than those put forth by the IPCC. The Framework Convention on Climate Change, to which the United States and 191 other countries are signatories, calls for stabilizing concentrations of greenhouse gases in the atmosphere at a level that would avoid dangerous human interference with the climate system. What exactly constitutes such interference is subject to interpretation.

A variety of research studies suggest that a further 2°F increase (relative to the 1980-1999 period) would lead to severe, widespread, and irreversible impacts.82,83,84 To have a good chance (but not a guarantee) of avoiding temperatures above those levels, it has been estimated that atmospheric concentration of carbon dioxide would need to stabilize in the long term at around today’s levels.85,86,87,88

Reducing emissions of carbon dioxide would reduce warming over this century and beyond. Implementing sizable and sustained reductions in carbon dioxide emissions as soon as possible would significantly reduce the pace and the overall amount of climate change, and would be more effective than reductions of the same size initiated later. Reducing emissions of some shorter-lived greenhouse gases, such as methane, and some types of particles, such as soot, would begin to reduce the warming influence within weeks to decades.9

The graphs below show emissions scenarios and resulting carbon dioxide concentrations for three IPCC scenarios89,90 and one stabilization scenario.24

Scenarios of Future CO2 Global Emissions and Concentrations The graphs show recent and projected global emissions of carbon dioxide in gigatons of carbon, on the left, and atmospheric concentrations on the right under five emissions scenarios. The top three in the key are IPCC scenarios that assume no explicit climate policies (these are used in model projections that appear throughout this report). The bottom line is a “stabilization scenario,” designed to stabilize atmospheric carbon dioxide concentration at 450 parts per million. The inset expanded below these charts shows emissions for 1990-2010 under the three IPCC scenarios along with actual emissions to 2007 (in black). Image References: Nakicenovic and Swart Clarke et al. Marland et al. Tans91

The stabilization scenario is aimed at stabilizing the atmospheric carbon dioxide concentration at roughly 450 parts per million (ppm) this is 70 ppm above the 2008 concentration of 385 ppm. Resulting temperature changes depend on atmospheric concentrations of greenhouse gases and particles and the climate’s sensitivity to those concentrations.86 Of those shown in the figure above, only the 450 ppm stabilization target has the potential to keep the global temperature rise at or below about 3.5°F from pre-industrial levels and 2°F above the current average temperature, a level beyond which many concerns have been raised about dangerous human interference with the climate system.87,88 Scenarios that stabilize carbon dioxide below 450 ppm (not shown in the figure) offer an increased chance of avoiding dangerous climate change.87,88

Carbon dioxide is not the only greenhouse gas of concern. Concentrations of other heat-trapping gases like methane and nitrous oxide and particles like soot will also have to be stabilized at low enough levels to prevent global temperatures from rising higher than the level mentioned above. When these other gases are added, including the offsetting cooling effects of sulfate aerosol particles, analyses suggest that stabilizing concentrations around 400 parts per million of “equivalent carbon dioxide” would yield about an 80 percent chance of avoiding exceeding the 2°F above present temperature threshold. This would be true even if concentrations temporarily peaked as high as 475 parts per million and then stabilized at 400 parts per million roughly a century later.71,87,88,92,93,94 Reductions in sulfate aerosol particles would necessitate lower equivalent carbon dioxide targets.

Rising global temperature

Global Average Temperature 1900 to 2100 Observed and projected changes in the global average temperature under three IPCC no-policy emissions scenarios. The shaded areas show the likely ranges while the lines show the central projections from a set of climate models. A wider range of model types shows outcomes from 2 to 11.5ºF.90 Changes are relative to the 1960-1979 average. Image References: Smith et al.71 CMIP3-A92 All climate models project that human-caused emissions of heat-trapping gases will cause further warming in the future. Based on scenarios that do not assume explicit climate policies to reduce greenhouse gas emissions, global average temperature is projected to rise by 2 to 11.5°F by the end of this century89 (relative to the 1980-1999 time period). Whether the actual warming in 2100 will be closer to the low or the high end of this range depends primarily on two factors: first, the future level of emissions of heat-trapping gases, and second, how sensitive climate is to past and future emissions. The range of possible outcomes has been explored using a range of different emissions scenarios, and a variety of climate models that encompass the known range of climate sensitivity.

Changing precipitation patterns

Projections of changes in precipitation largely follow recently observed patterns of change, with overall increases in the global average but substantial shifts in where and how precipitation falls.89 Generally, higher latitudes are projected to receive more precipitation, while the dry belt that lies just outside the tropics expands further poleward,95,96 and also receives less rain. Increases in tropical precipitation are projected during rainy seasons (such as monsoons), and especially over the tropical Pacific. Certain regions, including the U.S. West (especially the Southwest) and the Mediterranean, are expected to become drier. The widespread trend toward more heavy downpours is expected to continue, with precipitation becoming less frequent but more intense.89 More precipitation is expected to fall as rain rather than snow.

Currently rare extreme events are becoming more common

In a warmer future climate, models project there will be an increased risk of more intense, more frequent, and longer-lasting heat waves.89 The European heat wave of 2003 is an example of the type of extreme heat event that is likely at least two-thirds chance of occurring to become much more common.89 If greenhouse gas emissions continue to increase, by the 2040s more than half
of European summers will be hotter than the summer of 2003, and by the end of this century, a summer as hot as that of 2003 will be considered unusually cool.77

Global Increase in Heavy Precipitation 1900-2100 Simulated and projected changes in the amount of precipitation falling in the heaviest 5 percent of daily events. The shaded areas show the likely ranges while the lines show the central projections from a set of climate models. Changes are relative to the 1960-1979 average. Image Reference: CMIP3-A92

Increased extremes of summer dryness and winter wetness are projected for much of the globe, meaning a generally greater risk of droughts and floods. This has already been observed,57 and is projected to continue. In a warmer world, precipitation tends to be concentrated into heavier events, with longer dry periods in between.89

Models project a general tendency for more intense but fewer storms overall outside the tropics, with more extreme wind events and higher ocean waves in a number of regions in association with those storms. Models also project a shift of storm tracks toward the poles in both hemispheres.89

Changes in hurricanes are difficult to project because there are countervailing forces. Higher ocean temperatures lead to stronger storms with higher wind speeds and more rainfall.97 But changes in wind speed and direction with height are also projected to increase in some regions, and this tends to work against storm formation and growth.98,99,100 It currently appears that stronger, more rain-producing tropical storms and hurricanes are generally more likely, though more research is required on these issues.66 More discussion of Atlantic hurricanes, which most affect the United States, appears in the National Climate Change section.

Sea level will continue to rise

Projecting future sea-level rise presents special challenges. Scientists have a well-developed understanding of the contributions of thermal expansion and melting glaciers to sea-level rise, so the models used to project sea-level rise include these processes. However, the contributions to past and future sea-level rise from ice sheets are less well understood. Recent observations of the polar ice sheets show that a number of complex processes control the movement of ice to the sea, and thus affect the contributions of ice sheets to sea-level rise.30 Some of these processes are already producing substantial loss of ice mass. Because these processes are not well understood it is difficult to predict their future contributions to sea-level rise.101

Because of this uncertainty, the 2007 assessment by the IPCC could not quantify the contributions to sea-level rise due to changes in ice sheet dynamics, and thus projected a rise of the world’s oceans from 8 inches to 2 feet by the end of this century.89

More recent research has attempted to quantify the potential contribution to sea-level rise from the accelerated flow of ice sheets to the sea28,41 or to estimate future sea level based on its observed relationship to temperature.102 The resulting estimates exceed those of the IPCC, and the average estimates under higher emissions scenarios are for sea-level rise between 3 and 4 feet by the end of this century. An important question that is often asked is, what is the upper bound of sea-level rise expected over this century? Few analyses have focused on this question. There is some evidence to suggest that it would be virtually impossible to have a rise of sea level higher than about 6.5 feet by the end of this century.41

The changes in sea level experienced at any particular location along the coast depend not only on the increase in the global average sea level, but also on changes in regional currents and winds, proximity to the mass of melting ice sheets, and on the vertical movements of the land due to geological forces.103 The consequences of sea-level rise at any particular location depend on the amount of sea-level rise relative to the adjoining land. Although some parts of the U.S. coast are undergoing uplift (rising), most shorelines are subsiding (sinking) to various degrees – from a few inches to over 2 feet per century.

Abrupt climate change

There is also the possibility of even larger changes in climate than current scenarios and models project. Not all changes in the climate are gradual. The long record of climate found in ice cores, tree rings, and other natural records show that Earth’s climate patterns have undergone rapid shifts from one stable state to another within as short a period as a decade. The occurrence of abrupt changes in climate becomes increasingly likely as the human disturbance of the climate system grows.89 Such changes can occur so rapidly that they would challenge the ability of human and natural systems to adapt.104 Examples of such changes are abrupt shifts in drought frequency and duration. Ancient climate records suggest that in the United States, the Southwest may be at greatest risk for this kind of change, but that other regions including the Midwest and Great Plains have also had these kinds of abrupt shifts in the past and could experience them again in the future.

Rapid ice sheet collapse with related sea-level rise is another type of abrupt change that is not well understood or modeled and that poses a risk for the future. Recent observations show that melting on the surface of an ice sheet produces water that flows down through large cracks that create conduits through the ice to the base of the ice sheet where it lubricates ice previously frozen to the rock below.30 Further, the interaction with warm ocean water, where ice meets the sea, can lead to sudden losses in ice mass and accompanying rapid global sea-level rise. Observations indicate that ice loss has increased dramatically over the last decade, though scientists are not yet confident that they can project how the ice sheets will respond in the future.

There are also concerns regarding the potential for abrupt release of methane from thawing of frozen soils, from the sea floor, and from wetlands in the tropics and the Arctic. While analyses suggest that an abrupt release of methane is very unlikely to occur within 100 years, it is very likely at least a 90% chance of occurring that warming will accelerate the pace of chronic methane emissions from these sources, potentially increasing the rate of global temperature rise.105

A third major area of concern regarding possible abrupt change involves the operation of the ocean currents that transport vast quantities of heat around the globe. One branch of the ocean circulation is in the North Atlantic. In this region, warm water flows northward from the tropics to the North Atlantic in the upper layer of the ocean, while cold water flows back from the North Atlantic to the tropics in the ocean’s deep layers, creating a “conveyor belt” for heat. Changes in this circulation have profound impacts on the global climate system, from changes in African and Indian monsoon rainfall, to atmospheric circulation relevant to hurricanes, to changes in climate over North America and Western Europe.

Recent findings indicate that it is very likely at least a 90% chance of occurring that the strength of this North Atlantic circulation will decrease over the course of this century in response to increasing greenhouse gases. This is expected because warming increases the melting of glaciers and ice sheets and the resulting runoff of freshwater to the sea. This additional water is virtually salt-free, which makes it less dense than sea water. Increased precipitation also contributes fresh, less-dense water to the ocean. As a result, less surface water is dense enough to sink, thereby reducing the conveyor belt’s transport of heat. The best estimate is that the strength of this circulation will decrease 25 to 30 percent in this century, leading to a reduction in heat transfer to the North Atlantic. It is considered very unlikely that this circulation would collapse entirely during the next 100 years or so, though it cannot be ruled out. While very unlikely, the potential consequences of such an abrupt event would be severe. Impacts would likely include sea-level rise around the North Atlantic of up to 2.5 feet (in addition to the rise expected from thermal expansion and melting glaciers and ice sheets), changes in atmospheric circulation conditions that influence hurricane activity, a southward shift of tropical rainfall belts with resulting agricultural impacts, and disruptions to marine ecosystems.75

6.5: The Overall Impact of Climate Change - Biology

As global greenhouse gases are projected to hit a new high for 2019, Petteri Taalas of the World Meteorological Organization recently declared, “Things are getting worse.” A 2019 poll found that only 24 percent of U.S. respondents believed climate change would have a great deal of impact on their lives 31 percent believed it would have a fair amount of impact.

Different regions of the country will be affected in different ways, some more than others. But there are certain impacts that will probably affect every American’s way of life. Here are 10 of them.

1. Damage to your home

Floods, the most common and deadly natural disasters in the U.S., will likely be exacerbated and intensified by sea level rise and extreme weather. Heavy precipitation is projected to increase throughout the century to potentially three times the historical average. A 2018 study found that over 40 million Americans are at risk of flooding from rivers, and over 8.6 million people live in areas that already experience coastal flooding from storm surges during hurricanes. FEMA estimated that even one inch of floodwater in an average-sized home could cost homeowners almost $27,000 in damages.

In September, Adam Sobel, founding director of Columbia University’s Initiative on Extreme Weather and Climate, testified before the House Science, Space and Technology Committee. He asserted that scientists have strong evidence that global warming will increase the frequency or intensity of heavy rain events, and coastal flooding due to hurricane storm surge is also worsening because of sea level rise and increased precipitation.

In addition, he said, the frequency and intensity of droughts and wildfires are on the rise. While no state is immune to wildfires, 13 states in the West are considered susceptible to the most severe wildfire damage, with California having the most acres burned in 2018. A national analysis found that 775,654 homes are at extreme risk of wildfire in these 13 states. But even if homes do not burn to the ground, they may suffer smoke and fire damage, as well as water damage and flooding from fire fighting efforts.

How to protect yourself

  • Apply sealants and coatings to prevent floodwaters from entering your house
  • Install a sump pump
  • Keep your gutters and drains clear
  • Where flooding occurs regularly, raise your home up on stilts or piles
  • Remove dry vegetation around the house
  • When replacing a roof, opt for tile or metal
  • Take all evacuation warnings seriously and have an emergency supply kit ready to go

2. More expensive home insurance

As insurance companies pay out huge amounts to homeowners whose houses have been damaged by climate change impacts, many are raising premiums to offset their costs. Home insurance rates increased more than 50 percent between 2005 and 2015.

In high-risk areas, premiums and deductibles may rise, coverage may be more limited, and insurance could ultimately become unaffordable or unavailable for some, especially in climate-vulnerable areas. For Connecticut homeowners, insurance rates have gone up 35 percent in the last 10 years for homeowners with property along the coast, rates have gone up by over 50 percent. In 2016, California insurance companies would not renew over 10,000 policies for homes in high-risk areas. (Recently, however, the state issued a one-year moratorium preventing insurers from dropping customers who live in areas at risk from wildfire.) Travelers Insurance Company now requires separate deductibles in areas where hurricanes and tornadoes are more common.

Moreover, standard homeowners’ insurance does not cover flooding, so homeowners must buy private insurance or sign up for the National Flood Insurance Program run by FEMA. Due to billions of dollars in payouts for Hurricanes Katrina, Harvey, Irma, Maria and Sandy, however, NFIP is $20.5 billion in debt. In October, FEMA announced that rates would rise 11.3 percent in April 2020, and will be further restructured in October 2021.

How to protect yourself

  • When choosing a home, factor in climate risks
  • Check FEMA flood maps (even though almost 60 percent are out of date)
  • Understand your insurance coverage and needs
  • Shop around for your insurance policy
  • Raise your deductible for lower monthly payments
  • Make your home more disaster-resistant

3. Outdoor work could become unbearable

With continued global warming, heat waves are expected to increase in frequency, duration and intensity. Jane Baldwin, a postdoctoral research scientist at Lamont-Doherty Earth Observatory, found that compound heat waves—heat waves that occur in sequence, one after the other—will also increase, making recovery from heat waves more difficult.

Agricultural workers in California Photo: Holgerhubbs

People who work outdoors, such as construction workers, miners, firefighters and agricultural workers, will be most affected by increasing temperatures. Florida, for example, has one of the highest rates of heat-related hospitalizations in the U.S. This summer during a heat wave, the majority of heat-related visits to emergency rooms in Virginia were made by people aged 29-40, 70 percent of whom were men. Indoor workers in warehouses and steel plants can also be affected by excessive heat.

One study suggested that outdoor workers should begin their shifts earlier in the day, but if global warming continues at the current pace, by 2100, they would have to start working four to six hours before dawn. Currently, there are no federal laws that protect workers from heat stress, but in July, a bill was introduced into the House of Representatives that would require the Occupational Safety and Health Administration to establish standards to protect those working in the heat.

How to protect yourself

  • Take frequent shade and water breaks
  • Use a damp rag to keep cool
  • Wear light-colored clothing and a hat
  • Know the symptoms of heat exhaustion and heat stroke

4. Higher electric bills and more blackouts

As temperatures rise, people will need to stay cool for health and comfort reasons. Climate Central analyzed 244 cities in the U.S. and determined that 93 percent experienced an increase in the number of days that required extra cooling to remain comfortable. As we rely more heavily on air conditioners and fans, electricity bills will get higher.

The increased demand for electricity, especially during peak periods, can also over-tax the electrical grid, triggering brownouts or blackouts. Extreme weather, such as hurricanes, heat waves or snowstorms, can cause power outages too.

Blackout in NYC after Hurricane Sandy
Photo: David Shankbone

Between the mid-1980s and 2012, there was a ten-fold increase in power outages, 80 percent of which were caused by weather.

As wildfires plague California, Pacific Gas & Electric has been preemptively shutting down power to avoid the possibility of sparking fires in the dry, windy conditions. Millions lost power during this year’s blackouts. Pre-emptive blackouts could become a common occurrence.

Brownouts or blackouts can also result if hydropower plants have less water to draw from in rivers and lakes, and if water becomes too warm to cool nuclear or coal power plants.

How to protect yourself

  • Find greener ways to stay cool
  • Install a programmable thermostat and set the temperature higher
  • Run your appliances at night
  • During a blackout, fill the bathtub so you have water to flush toilets keep freezers and refrigerators closed
  • If the power goes out, unplug appliances and electronics to avoid damage from electrical surges
  • Don’t run generators inside the garage or near open windows, to avoid carbon monoxide poisoning

5. Rising taxes

Municipalities are recognizing the need to make their communities more resilient in the face of climate change impacts. Although measures such as building seawalls or hardening infrastructure are hugely expensive, the National Climate Assessment determined that resiliency measures save money in the long run — for example, by reducing coastal property damage to about $800 billion from a projected $3.5 trillion. Paying for mitigation and adaptation measures, however, will likely have to be funded through higher property taxes or “resilience fees.”

Grand Rapids, Michigan had problems with flooding and aging stormwater infrastructure. In 2014, the residents rejected a 13.3 percent income tax cut in order to implement green infrastructure measures that absorb runoff and reduce flooding on streets.

Flooding in Norfolk, Virginia Photo: D. Loftis/VIMS.

In 2018, Norfolk, VA, which is surrounded by water and vulnerable to sea level rise, approved a .10 increase to the real estate tax rate, which will go towards citywide resiliency plans to address flooding. And in the wake of California’s recent wildfires, Marin County is proposing a .10 per square foot parcel tax on property owners across the county to fund wildfire prevention.

How to protect yourself

  • See if you qualify for a tax rebate or credit for renewable energy and/or energy efficiency
  • Check to see if your state gives tax exemptions for seniors, veterans, or the disabled

6. More allergies and other health risks

Warmer temperatures cause the pollen season to be longer and worsen air quality, both of which can result in more allergy and asthma attacks. Ground-level ozone, a major component of smog, which increases when temperatures warm, can also cause coughing, chest tightness or pain, decrease lung function and worsen asthma and other chronic lung diseases.

In addition, after floods or storms, damp buildings may foster mold growth, which has been linked to allergies and other lung diseases.

With rising temperatures, more people will suffer heat cramps, heat exhaustion, hyperthermia (high body temperature) and heat stroke as days that are unusually hot for the season hamper the body’s ability to regulate its temperature. Prolonged exposure to heat can exacerbate cardiovascular, respiratory and kidney diseases, diabetes, and increase the chance for strokes.

Older adults, pregnant women, and children are particularly vulnerable to excess heat. A 2018 paper, written by Madeline Thomson while she was a senior researcher at the Earth Institute’s International Research Institute for Climate and Society, called attention to the fact that children and infants are more vulnerable to dehydration and heat stress, as well as to respiratory disease, allergies and fever during heat waves and to the need for adults to protect them.

As the climate changes, disease-carrying mosquitoes are extending their range, bringing diseases such as malaria, dengue fever, chikungunya and West Nile virus farther north than they’ve ever been. In the summer of 2013, the Aedes aegypti mosquito, usually found in Texas and the southeastern U.S., suddenly appeared in California as far north as San Francisco — fortunately, none of the tested mosquitoes carried dengue or yellow fever. One study projects that Aedes aegypti could reach as far north as Chicago by 2050.

Heat waves, natural disasters, and the disruption in lives they cause can also aggravate mental health. During one recent California wildfire, suicidal and traumatized people flooded emergency rooms.

How to protect yourself

  • When pollen counts are high or air quality is bad, stay indoors
  • During a heat wave, limit outside activity during the hottest hours
  • Stay hydrated
  • Use insect repellent
  • Understand how climate impacts can affect your children and take precautions for them

7. Food will be more expensive and variety may suffer

In the last 20 years, food prices have risen about 2.6 percent each year, and the USDA expects that food prices will continue to rise. While there are several reasons for higher food prices, climate change is a major factor. Extreme weather affects livestock and crops, and droughts can have impacts on the stability and price of food. New York apple farmers, for example, are facing warmer winters and extreme weather, which can wipe out harvests. They are trying to save their apples with new irrigation systems and wind machines that blow warm air during cold spells, but eventually these added costs will be reflected in the price of apples.

As temperatures warm and precipitation increases, more pathogens will thrive and affect plant health in addition, more food will spoil. And because food is a globally traded commodity today, climate events in one region can raise prices and cause shortages across the globe. For example, a drought in Brazil in 2013 and 2014 caused Arabica coffee prices to double.

Michael Puma, director of the Earth Institute’s Center for Climate Systems Research, studies global food security, especially how susceptible the global network of food trade is to natural (e.g., megadroughts, volcanic eruptions) and manmade (e.g., wars, trade restrictions) disturbances. He and his colleagues are building quantitative economic models to examine vulnerabilities in the food system under different scenarios they will use the tool to explore how altering certain policies might reduce the vulnerabilities of the food system to disruptions.

Three-quarters of our crops rely on insects for pollination and scientists believe 41 percent of insect species are threatened with extinction. While habitat loss is the major reason, climate change also plays a large part. If we lose pollinators, that could mean losing some of the crops and varieties they pollinate.

How to protect yourself

  • To save money, cook at home more often and avoid purchasing prepared foods
  • Don’t waste food
  • Buy in bulk
  • Eat less meat

8. Water quality could suffer

Intense storms and heavy precipitation can result in the contamination of water resources. In cities, runoff picks up pollutants from the streets, and can overflow sewage systems, allowing untreated sewage to enter drinking water supplies.

In rural areas, runoff transports animal waste, pesticides and chemical fertilizer, and can enter drinking or recreational waters. Polluted drinking water can cause diarrhea, Legionnaires’ disease, and cholera it can also cause eye, ear and skin infections. In some low-lying coastal areas, sea level rise could enable saltwater to enter groundwater drinking water supplies. And in areas suffering from drought, contaminants become more concentrated as water supplies decrease. In addition, algal blooms thrive in warm temperatures and can contaminate drinking water. In 2014, residents of Toledo, Ohio had to drink bottled water for three days because their water supply was polluted with cyanobacteria toxins.

The Earth Institute’s Columbia Water Center studies the state of fresh water availability in the face of climate change, and the water needs of food production, energy generation and ecosystems. It aims to provide “sustainable models of water management and development” to apply on local, regional and global levels.

How to protect yourself

  • Don’t use water you suspect is contaminated to wash dishes, brush teeth, wash or prepare food, make ice, wash hands or make baby formula
  • Keep bottled water on hand
  • Decrease your household water use, especially during droughts
  • Heed government precautions when drinking water is found to be contaminated and boil your water

9. Outdoor exercise and recreational sports will become more difficult

Reduced snowfall and early snowmelt in the spring will have an impact on skiing, snowmobiling and other winter sports. Less water in lakes and rivers could also affect boating and fishing during summer.

Hotter temperatures, especially in the South and Southwest, will make summer activities like running, biking, hiking and fishing less comfortable and potentially dangerous to your health.

How to protect yourself

  • Shorten your outdoor workout
  • Substitute indoor activities when temperatures are excessively hot
  • Plan outdoor exercise for early or late in the day
  • Choose shady routes if possible
  • Stay hydrated
  • Wear loose, light-colored clothing
  • Keep salty or juicy snacks on hand
  • Know the signs of heat cramps, heat exhaustion and heatstroke

10. Disruptions in travel

As temperatures rise, it may get too hot for some planes to fly. In 2015, Radley Horton, associate research professor at Lamont-Doherty Earth Observatory, and then Ph.D. student Ethan Coffel published a study calculating how extreme heat could restrict the takeoff weight of airplanes. Hotter air is less dense, so planes get less lift under their wings and engines produce less power. Airlines may be forced to bump passengers or leave luggage behind to lighten their loads. This concern is one reason why long-distance flights from the Middle East leave at night the practice could become standard for the U.S. as well.

Flights can be disrupted due to flooding because many airports are located on low-lying land.

LaGuardia Airport after Hurricane Sandy Photo: peoples world

Superstorm Sandy in 2012 flooded LaGuardia Airport for three days. One runway in Northern Canada had to be repaved because the permafrost on which it was built began melting.

Once in the air, you may experience more turbulence. Stronger winds create more shear (a difference in wind speed over a short distance) in the atmosphere, which results in turbulence. And distant storms can create waves in the atmosphere that cause turbulence hundreds of miles away.

Recreational travel could be upended as climate change impacts many popular destinations. Sea level rise, storm surge and erosion are affecting Waikiki Beach in Hawaii, Miami Beach in Florida, and Copacabana in Rio de Janeiro. Along Florida’s southwest and Gulf coasts, toxic algae blooms have killed fish and turtles, sending the stench and toxins into the air, and making beaches unpleasant and unhealthy.

In the U.S., Montana’s Glacier National Park is losing its glaciers in 1910 it had more than 100, but now fewer than two dozen remain. The Everglades are experiencing salt water intrusion from sea level rise. World heritage sites, too, are being affected by global warming impacts: The Amazon rainforest is threatened by logging and fires, the Arctic is thawing, the snows of Kilamanjaro are melting, and the Great Barrier Reef’s corals are bleaching.

How to protect yourself

  • Change your travel destination
  • Purchase travel insurance
  • Check the weather of your travel destination
  • Fly during the morning to reduce chances of thunderstorms and turbulence
  • On the plane, keep your seat belt buckled as much as possible

As global temperatures continue to rise, climate change will affect our wallets, our health, our safety, and our lives. Many people are already feeling these impacts. And while there are ways to adapt on a personal level, some of these changes are going to become more severe and unavoidable over time. The best way to protect ourselves for the future is to support policies and measures that cut carbon emissions and enhance climate resilience.

The Impacts of Climate Change on Phenology: A Synthesis and Path Forward for Adaptive Management in the Pacific Northwest

Phenology, or the timing of the annual cycles of plants and animals, is extremely sensitive to changes in climate. We know that plants and animals may adjust the timing of certain phenological events, such as tree flowering or migration, based on changes in weather. However, it’s important that we also understand how the timing of phenological events is changing over longer time frames, as clim.

Phenology, or the timing of the annual cycles of plants and animals, is extremely sensitive to changes in climate. We know that plants and animals may adjust the timing of certain phenological events, such as tree flowering or migration, based on changes in weather. However, it’s important that we also understand how the timing of phenological events is changing over longer time frames, as climate conditions change.

While some species appear to be adjusting to the increase in unseasonal temperatures, drought, and extreme storms that have come with climate change, not all species are responding at the same speed or in the same ways. This can disrupt the manner in which species interact and the way that ecosystems function overall. For example, plants may bloom before butterflies emerge to pollinate them, or caterpillars may emerge before migratory birds arrive to feed them to their young.

For natural resource managers, understanding how changing climate conditions are impacting plant and animal phenology is essential for making effective adaptive management decisions. This project will support management needs in the Pacific Northwest by synthesizing and communicating what we know about the impacts of climate change on phenology in the region, as well as identifying what gaps exist in the research and what tools are available to support management planning. The resulting products will be user-friendly and relevant to a wide range of natural resource managers seeking applied solutions and adaptation options for a range of issues, including land management, wildlife and habitat conservation, and recreation.

More Fire

Imagine visiting the park to find your favorite view obscured by smoke or whole areas closed for public safety. Imagine struggling to breathe or having to evacuate your campsite in the middle of the night. In recent years, many visitors to Glacier have experienced all of these things. Scientists estimate that climate change has doubled the amount of acres burned in western US wildfires since the 1980s. This trend, including an increase in size, frequency, and severity of wildfires, is expected to continue.

Reptiles and Climate Change

Many reptiles are highly sensitive to the altered temperatures that may result from climate change due to their ectothermy which requires that they rely on ambient environmental temperatures to maintain critical physiological processes. Due to the variety of snakes, lizards, crocodilians, and turtles in our world (traditionally classified as reptiles), and because climate change data and projections vary with location, it will be important to consider each species and location separately when considering the potential effects of altered climate on these animals.

In temperate zones, lizards are thought to be highly vulnerable to climate change (1-7). Their reproduction is closely tied to narrow windows of time in the spring and summer when suitable temperature and moisture regimes are available for critical natural history activities, such as foraging and mating. Altered weather conditions during these seasons may result in frequently recurring "bust" years of reproductive failure. Other climate effects on lizard survival include mortality associated with warm spells in winter (8), interacting effects of altered vegetation communities, fire regimes and invasive species (9), and potentially disease (10).
Snakes are very closely related to lizards, and these effects may hold true for them as well. Just as with lizards, new studies illustrate species differences: climatic niche models suggest that some rattlesnakes may have smaller ranges (11) while ratsnakes have increased activities due to warmer night temperatures (12).

Climate change concerns for turtles and crocodilians are three-fold. First, these mostly aquatic species may encounter altered habitats and increased habitat fragmentation with altered climate. In this regard they share many concerns with amphibians, such as sensitivity to changes in water availability and its’ thermal properties. Second, turtles and alligators have temperature-sensitive sex determination: cooler temperatures may produce nests of only males warmer temperatures may produce nests of only females. Temperature changes in a local area may have the effect of altering the sex ratios of populations - potentially affecting future reproduction and over time compromising their evolutionary fitness (13). Third, coastal species such as the American Alligator and Crocodile are susceptible to an increasing frequency or intensity of storms caused by increases in ocean temperatures. Storm surges can displace or drown animals, and dehydrate them by salt water intrusion into freshwater habitats (14). Because the United States is a biodiversity hotspot for turtles, and turtle conservation issues are multi-faceted, concern for climate change projections relative to rare turtle species is a specific concern (15).

Likely Changes

The highest biodiversity of reptiles in the United States is in the southern states, in desert and subtropical ecosystems. The northern distributions are constrained by latitude, with species richness dropping considerably as you go north. North boundaries of species ranges are often marginal habitats due to climate factors such as cool temperatures and weather variation. Altered thermal niches (4, 5) for reptiles in these zones due to climate change will be important to track. Briefly, to understand thermal niches, consider that there is a time-window during the day when there are suitable temperatures for reptile activities. It appears that this time-window is becoming smaller as climate changes are apparent in both tropical and temperate zone regions, reducing the activity times of reptiles, affecting their reproduction and survival. Although habitat may be marching northward or into mountains for some species, for other species, increased weather variation may alter the frequency or intensity of boom-bust reproductive cycles and cohort survival. Examples follow.

In Oregon, variable spring weather has been shown to narrow the time window of suitable breeding conditions for the Common Side-blotched Lizard, Uta stansburiana, with reproductive bust years being reported (6, 7). In Mexico, a study reported that 12% of local lizard populations have been lost since 1975, with evidence that these losses are associated with climate change altering thermal niches (4). In Alberta, Canada, the Greater Short-horned Lizard, Phrynosoma hernandesi, overwinter survival relies on persistent snow cover to retain animals in insulated hibernation: lizards become active during warm spells in winter, and then they can be ‘caught out’ and die when it snows again (8). In contrast, ratsnake thermal niches may be expanding with more warmer nights (12).

Vulnerability assessments and predictions of how habitat distributions will change abound for many taxa. Looming questions are where will suitable habitats occur in the future, and will organisms be able to get there? In our human-altered world, roads and urban-rural development are new hurdles to dispersing reptiles, added to a variety of natural geographic barriers. In Spain, the northward expansion of lizard ranges coincident with changing climate has been tracked over about a 50 year period, with geographic barriers including the Pyrenees Mountains now posing dispersal limitations (3).

Options for Management

For reptiles, management is of paramount concern to maintain and restore existing habitats, augment acreages of intact habitat blocks, and adapt management actions to reduce environmental stressors (see regional Habitat Management Guidelines at: Because microclimates can be readily manipulated with local land management activities, people can actively engineer a future for some of these organisms, especially when their environments are already highly altered due to human activities.

Invasive plant species and most human disturbances can alter local- to landscape-scale habitats and microclimates, which can have consequent effects on reptiles. Non-native vegetation may have different physical structure and cover, hindering reptile daily activities, and subsequently altering critical life history functions and reptile survival, and negatively influencing dynamics of interacting communities. Open habitat management may be needed to forestall encroaching vegetation, especially non-native plants, or to mitigate human disturbance (e.g., agricultural or energy development). Meadow shrub and tree control may be needed to retain sun-exposure. Riparian buffers may retain near-water refugia. For turtles or other water-dependent reptiles, manipulation of hydroperiod at sites by site excavation and riparian buffer management are considerations. Substrate management may be needed for several types of reptiles: rock outcrops and talus are complex refugia for lizards and snakes and may need protection or augmentation rocky pond edges provide basking sites and antipredation refugia for turtles. Some species need specific substrate types, or rely on existing burrows created by other animals these need consideration if climate change alters landscape-scale habitat distribution. Traditionally used snake hibernacula may need special protection. Management measures taken to maintain natural fire regimes and control invasive plants might also benefit reptiles. Altered fire regimes may change refugia, reduce cover and expose animals to heightened predation, and invasive plants may exacerbate climate-linked fire patterns.

Managers can facilitate the movement of reptiles by providing corridors between needed habitats that support complex reptile life histories: breeding, foraging, overwintering, anti-predation, and basking habitats can all differ. Corridors between overwintering hibernacula and foraging areas, or between upland nesting sites and aquatic breeding sites are a particular concern because these can be inadvertently affected by roads or development. Considerations include: 1) extension of riparian corridors along safe upland dispersal routes 2) creating barriers to dispersal along unsafe routes, such as along roads or into disturbed areas 3) road-crossing culverts that may require dry as well as wetted channel areas 4) management of surface rock or burrow availability and connectivity.

Figure ES1: Examples of Climate Impacts on Human Health

Climate change is a significant threat to the health of the American people. The impacts of human-induced climate change are increasing nationwide. Rising greenhouse gas concentrations result in increases in temperature, changes in precipitation, increases in the frequency and intensity of some extreme weather events, and rising sea levels. These climate change impacts endanger our health by affecting our food and water sources, the air we breathe, the weather we experience, and our interactions with the built and natural environments. As the climate continues to change, the risks to human health continue to grow.

Current and future climate impacts expose more people in more places to public health threats. Already in the United States, we have observed climate-related increases in our exposure to elevated temperatures more frequent, severe, or longer-lasting extreme events degraded air quality diseases transmitted through food, water, and disease vectors (such as ticks and mosquitoes) and stresses to our mental health and well-being. Almost all of these threats are expected to worsen with continued climate change. Some of these health threats will occur over longer time periods, or at unprecedented times of the year some people will be exposed to threats not previously experienced in their locations. Overall, instances of potentially beneficial health impacts of climate change are limited in number and pertain to specific regions or populations. For example, the reduction in cold-related deaths is projected to be smaller than the increase in heat-related deaths in most regions.

Every American is vulnerable to the health impacts associated with climate change. Increased exposure to multiple health threats, together with changes in sensitivity and the ability to adapt to those threats, increases a person’s vulnerability to climate-related health effects. The impacts of climate change on human health interact with underlying health, demographic , and socioeconomic factors. Through the combined influence of these factors, climate change exacerbates some existing health threats and creates new public health challenges. While all Americans are at risk, some populations are disproportionately vulnerable, including those with low income, some communities of color, immigrant groups (including those with limited English proficiency), Indigenous peoples, children and pregnant women, older adults, vulnerable occupational groups, persons with disabilities, and persons with preexisting or chronic medical conditions.

In recent years, scientific understanding of how climate change increases risks to human health has advanced significantly. Even so, the ability to evaluate, monitor, and project health effects varies across climate impacts. For instance, information on health outcomes differ in terms of whether complete, long-term datasets exist that allow quantification of observed changes, and whether existing models can project impacts at the timescales and geographic scales of interest. Differences also exist in the metrics available for observing or projecting different health impacts. For some health impacts, the available metrics only describe changes in risk of exposure, while for others, metrics describe changes in actual health outcomes (such as the number of new cases of a disease or an increase in deaths).

This assessment strengthens and expands our understanding of climate-related health impacts by providing a more definitive description of climate-related health burdens in the United States. It builds on the 2014 National Climate Assessment 5 and reviews and synthesizes key contributions to the published literature. Acknowledging the rising demand for data that can be used to characterize how climate change affects health, this report assesses recent analyses that quantify observed and projected health impacts. Each chapter characterizes the strength of the scientific evidence for a given climate–health exposure pathway or “link” in the causal chain between a climate change impact and its associated health outcome. This assessment’s findings represent an improvement in scientific confidence in the link between climate change and a broad range of threats to public health, while recognizing populations of concern and identifying emerging issues. These considerations provide the context for understanding Americans’ changing health risks and allow us to identify, project, and respond to future climate change health threats. The overall findings underscore the significance of the growing risk climate change poses to human health in the United States.

U.K. Requires Companies to Report on Climate Change by 2025

The U.K.’s Chancellor of the Exchequer Rishi Sunak on Monday said the country would require companies to report on the business impacts of climate change.

Dieter Holger

Emese Bartha

The U.K. said that companies need to report the financial impacts of climate change on their businesses within the next five years, becoming the first country to make the disclosures mandatory as investors and governments demand corporations curb their greenhouse gas emissions.

Chancellor of the Exchequer Rishi Sunak, the country’s equivalent to a U.S. Treasury secretary, said Monday that the rule would apply to most of the nation’s economy, including listed companies, banks, large private businesses, insurers, asset managers and regulated pension funds.

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“We are starting a new chapter in the history of financial services and renewing the UK’s position as the world’s pre-eminent financial centre,” Mr. Sunak said. “By taking as many equivalence decisions as we can in the absence of clarity from the EU, we’re doing what’s right for the UK and providing firms with certainty and stability.”

By 2025, he said those groups must report in alignment with the Task Force on Climate-related Financial Disclosures, an organization established in 2015 by the international Financial Stability Board to promote more informed decisions by companies.

The TCFD says companies should disclose in their financial reports how climate change could increase or reduce sales, among other issues. As of this year, more than 1,500 organizations have expressed their support for the TCFD’s recommendations, a more than 85% increase from last year, according to the TCFD’s status report published late last month. The report said 42% of companies with a market capitalization above $10 billion disclosed at least some information in line with the TCFD.

U.S. businessman and politician Michael Bloomberg is chairman of the TCFD. “Today’s news is the latest and biggest sign of how countries have embraced the concept, and we commend the U.K. for its leadership,” he said in an email. “Clearer data on the impacts of climate change will help countries world-wide build greener and more resilient economies in the wake of the pandemic.”

Investment houses that offer environmental funds welcomed the U.K.’s adoption of the TCFD.

“Open, honest, consistent and transparent disclosure is a fundamental precondition for the realignment of finance and capitalism,” said Jenn-Hui Tan, global head of stewardship and sustainable investment at Fidelity International, commenting on the chancellor’s decision. The TCFD provides an essential platform for asset managers and companies alike to deliver this, Mr. Tan added.

The U.K.’s move comes as regulators in the U.S. have voiced support for the TCFD. Last month, Linda Lacewell, superintendent of the New York State Department of Financial Services, recommended that banks and insurers report through the TCFD. The DFS regulates around 1,500 banks, 1,800 insurers and other financial groups, with assets exceeding $7 trillion.

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Some investors say the U.S. could also move closer to requiring environmental, social and governance disclosures from companies under President-elect Joe Biden.

“New commissioners at the Securities and Exchange Commission would likely be supportive of mandating ESG disclosures by companies,” said Joe Keefe, president of Impax Asset Management. Mr. Biden would have an opportunity to replace Securities and Exchange Commission Chairman Jay Clayton, whose term expires in June next year.

Like the European Union it recently exited, the U.K. has a net-zero emissions goal by 2050. To help meet that goal, Mr. Sunak also said the country would issue its first green bond next year under its new climate change agenda, following its European peers. Money raised by issuing a green bond is earmarked for climate and environmental projects.

In early September, Germany raised 6.5 billion euros ($7.12 billion) via its debut green bond. The eurozone’s green sovereign bond market, which the U.K. isn’t part of, is still relatively small at less than around 1% of the region’s overall bond market, but it is expanding since France’s first green bond in January 2017.

&mdashMaitane Sardon contributed to this article.

Write to Dieter Holger at [email protected] and Emese Bartha at [email protected]

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The Weird Effect Climate Change Will Have On Plant Growth

A dd the hindering of plant growth to the long and growing list of the ways climate change may affect life on our planet. The number of days when plants can grow could decrease by 11% by 2100 assuming limited efforts to stall climate change, affecting some of the world’s poorest and most vulnerable people, according to a new study in PLOS Biology.

Climate change affects a number of variables that determine how much plants can grow. A 7% decline in the average number of freezing days will actually aid plant growth, according to the study, which relied on an analysis of satellite data and weather projections. At the same time, extreme temperatures, a decrease in water availability and changes to soil conditions will actually make it more difficult for plants to thrive. Overall, climate change is expected to stunt plant growth.

Declining plant growth would destroy forests and dramatically change the habitats that are necessary for many species to survive. And, if conditions get bad enough, forests could actually produce carbon instead of removing it from the atmosphere, exacerbating the root cause of climate change.

“Those that think climate change will benefit plants need to see the light, literally and figuratively,” said lead study author Camilo Mora, a professor at the University of Hawaii, in a statement.

The effects of climate change on plant growth will likely vary by region, with northern areas in places like Russia, China and Canada gaining growing days. But already hot tropical regions could lose as many as 200 growing days per year. In total, 3.4 billion people would live in countries that lose nearly a third of their growing days. More than 2 billion of those people live in low-income countries, according to the study.

The researchers’ findings sound pretty dire, but they acknowledge that these consequences would be the result of a worst-case scenario of sorts, one in which humans take minimal action to stem climate change. With strong or even moderate efforts, worldwide plant growth will fare much better, according to the study.

Anthropogenic climate change and allergen exposure: The role of plant biology

Accumulation of anthropogenic gases, particularly CO(2), is likely to have 2 fundamental effects on plant biology. The first is an indirect effect through Earth's increasing average surface temperatures, with subsequent effects on other aspects of climate, such as rainfall and extreme weather events. The second is a direct effect caused by CO(2)-induced stimulation of photosynthesis and plant growth. Both effects are likely to alter a number of fundamental aspects of plant biology and human health, including aerobiology and allergic diseases, respectively. This review highlights the current and projected effect of increasing CO(2) and climate change in the context of plants and allergen exposure, emphasizing direct effects on plant physiologic parameters (eg, pollen production) and indirect effects (eg, fungal sporulation) related to diverse biotic and abiotic interactions. Overall, the review assumes that future global mitigation efforts will be limited and suggests a number of key research areas that will assist in adapting to the ongoing challenges to public health associated with increased allergen exposure.

Watch the video: Climate Change: What Happens If The World Warms Up By 2C? (February 2023).