Science

Water and Global Climate Change: Potential Impacts on U.S. Water Resources

Water and Global Climate Change: Potential Impacts on U.S. Water Resources

By:
Kenneth D. Frederick, Resources for the Future
Peter H. Gleick, Pacific Institute for Studies in Development, Environment, and Security

Press Release

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Foreword

Eileen Claussen, Executive Director, Pew Center on Global Climate Change

Availability of an adequate, safe water supply is critical to the health, economy, and environment of any nation and its people. The United States, on average, is well-endowed with water. However, this year's spring floods and summer droughts illlustrate the importance of wide seasonal fluctuations in precipitation. Further, the growing conflicts over environmental and developmental water uses are an indication that water is becoming increasingly scarce.

Current scientific research shows that climate change will have major effects on precipitation, evapotranspiration, and runoff - and ultimately on the nation's water supply. Climate-induced changes in the water cycle likely will affect the magnitude, frequency, and costs of extreme weather events as well as the availability of water to meet growing demand. Recent reports, including "The Science of Climate Change," show that climate change is likely to increase the number of days of intense precipitation and the frequency of floods in northern latitudes and snowmelt-driven basins. The frequency and severity of droughts could also increase as a result of a decrease in total rainfall, as well as more frequent dry spells and greater evapotranspiration.

Because of uncertainties about changes in precipitation, many uncertainties exist in predicting specific regional impacts of large-scale changes. Still, some consistent impacts can be identified. In the arid and semiarid western United States, relatively modest changes in precipitation can have proportionally large impacts on water supplies. And in mountainous watersheds, higher temperatures will increase the ratio of rain to snow, accelerate the rate of spring snowmelt, and shorten the overall snowfall season, leading to more rapid, earlier, and greater spring runoff.

"Water and Global Climate Change" is the third in a series examining the potential impacts of climate change on the environment and society. This report identifies impacts not only to the quantity, but also to the quality of the water supply. Changes in stream flows, increased storm surges, and higher water temperatures all could negatively affect the health of the nation's water supply. An increase in the number of days of intense precipitation also could increase the agricultural and urban pollutants washed into streams and lakes. The resulting rise in sea level would contribute to saltwater intrusion into rivers, estuaries, and coastal aquifers.

The authors and the Pew Center are grateful for the input of Drs. John Boland, Kenneth Strzepek, and Barbara Miller, who reviewed previous drafts; and to Joel Smith and Brian Hurd of Stratus Consulting for their oversight of this Environmental Impacts series.

Executive Summary

The availability of freshwater to meet the demands of a growing and increasingly affluent population while sustaining a healthy environment has emerged as one of the nation's primary resource issues. Concerns about water are based in part on uncertainties over the availability of supplies stemming from the vicissitudes of the hydrologic cycle, growing populations, and the prospect that greenhouse gas-induced climate changes will alter the cycle in uncertain ways.

Global climatic changes will have major effects on precipitation, evapotranspiration, and runoff. But estimating the nature, timing, and even the direction of the impacts at the regional and local scales of primary interest to water planners involves many uncertainties. While specific regional impacts will depend on future climate changes as well as uncertain economic, institutional, and structural conditions, some consistent and robust results can be described.

In the relatively arid and semiarid western United States, modest changes in precipitation can have proportionally large impacts on water supplies. In mountainous watersheds, higher temperatures will increase the ratio of rain to snow, accelerate the rate of spring snowmelt, and shorten the overall snowfall season, leading to more rapid, earlier, and greater spring runoff. Because the temperature projections of climate models are less speculative than the projections of precipitation, temperature-induced shifts in the relative amounts of rain and snow and in the timing of snowmelt in mountainous areas are considered likely. Coping strategies should now be explored.

Where extensive water systems have been built, there are untapped opportunities for rethinking operating and management rules. At the same time, where water systems are already under stress because of limited supplies or water-quality problems, climatic changes may impose different and greater stresses than those already anticipated by water planners.

Climate-induced changes in hydrology will affect the magnitude, frequency, and costs of extreme events, which produce the greatest economic and social costs to humans. Flooding, the nation's most costly and destructive natural disaster, could become more common and extreme. Recent reports of the Intergovernmental Panel on Climate Change (IPCC) suggest that a greenhouse warming is likely to increase the number of intense precipitation days and flood frequencies in northern latitudes and snowmelt-driven basins. These reports also suggest that the frequency and severity of droughts could increase in some areas as a result of a decrease in total rainfall, more frequent dry spells, and greater evapotranspiration.

Many different general circulation models (GCMs) have been developed and improved over the past decades to understand the implications of increased concentrations of greenhouse gases on the climate. The ongoing National Assessment of the impacts of climate change on the United States is evaluating the implications of two different models - the Hadley and Canadian GCMs. Estimates of the impact of climate change on runoff within the water resource basins and subbasins in the conterminous United States using the outputs of these two general circulation models show similarities and sharp differences. For both models, temperatures and potential evapotranspiration rise significantly by 2100. But the uncertainties about the implications of climate change for water resources are illustrated by the contrasting projections of runoff based on these models. Estimates based on the Hadley model indicate flooding could increase in much of the country, while those based on the Canadian climate model indicate increased water scarcity would pervade much of the country. Both scenarios could result in sharply higher socioeconomic costs. Results based on these GCM outputs as well as more detailed regional studies emphasize two points: the detailed regional impacts of a greenhouse warming on future water supplies are uncertain, and runoff is sensitive to changes in temperature and precipitation.

Climatic changes will affect the demand as well as the supply of water. These changes may influence a wide range of water-system components, including reservoir operations, water quality, hydroelectric generation, and navigation. Irrigation, the largest consumer of U.S. water, is particularly sensitive to climate conditions; demand for irrigation water tends to increase as conditions become hotter and drier. Instream water uses such as hydroelectric power generation, navigation, recreation, and ecosystem maintenance are also sensitive to changes in the quantity, quality, and timing of runoff stemming from greenhouse warming.

Water is becoming increasingly scarce and expensive independent of climate change. Water demands are growing with population, incomes, and an appreciation for the values of instream ecological and recreational uses. Increased withdrawals of water for domestic, industrial, and agricultural uses, however, are limited by high economic costs and by the limited opportunities for increasing withdrawals from rivers or streams without adversely impacting instream uses. Improving the efficiency of our water use is rapidly becoming the primary means of balancing limited water supplies with growing demands. But as more people become dependent on a given water supply, vulnerability to drought can increase. Moreover, the capacity to store water to protect against floods and droughts and deal with the uncertainties of climate change appears to be declining because reservoir storage losses due to sedimentation have exceeded additions through new construction in recent years.

The impacts of climate change on water quality have received less attention than the impacts on quantity, but current research raises several concerns. Potential negative implications of climate change include reductions in dilution flows, increased storm surges, and higher water temperatures. Low flows in many western rivers will lead to increases in salinity levels to downstream water users; higher flows could help reduce some water quality concerns. Warmer water could threaten aquatic life directly as cool-water habitats disappear and indirectly as dissolved oxygen levels decline with higher temperatures. An increase in days with more intense precipitation could increase the agricultural and urban pollutants washed into streams and lakes, further reducing oxygen levels. Heavy rainfall is primarily responsible for soil erosion, leaching of agricultural chemicals, and runoff of urban and livestock wastes and nutrients into water bodies. Sea-level rise would contribute to saltwater intrusion into rivers and coastal aquifers.

The socioeconomic implications of both climate and non-climate impacts on water supply and demand will depend in large part on both the ability to adapt to change and on whether water managers and planners take action. Current laws and policies affecting water use, management, and development are often inefficient and unresponsive to changing conditions. The costs of these inefficiencies will likely rise if water becomes scarcer and supply and demand conditions change. There are four promising opportunities for reducing the costs and conflicts of supplying future water demands and adapting to future climate variability: (1) establishing incentives for using, conserving, and protecting supplies; (2) providing opportunities for transferring water among competing uses in response to changing conditions; (3) influencing how water is managed within and among basins; and (4) re-evaluating the operations of the existing infrastructure to address climate and non-climate changes.

All water-supply systems were designed and are operated on the assumption that future climate will look like past climate. Additional dams, reservoirs, aqueducts, levees, and other structures may eventually be needed to help adapt to climate change. But, when possible, costly and irreversible decisions to build water-related infrastructure should be postponed in anticipation of obtaining better information about the likely consequences and costs of a greenhouse warming. Water managers already have a wide variety of tools available for dealing with risk and uncertainty. One view holds that nothing different needs to be done now to cope with future climate changes as these tools will prove sufficient for dealing with future climate changes. But regional modeling studies suggest that even modest changes in climate can lead to changes in water availability outside the range of historical hydrologic variability. It is unclear whether some climate changes will be so rapid or of such large magnitude as to overwhelm existing systems before current management approaches can react. These uncertainties suggest the wisdom of re-examining design assumptions, operating rules, and contingency planning for a wider range of climate conditions than traditionally used. Maintaining options and building in flexibility are important for designing efficient water programs in the context of climate change.

About the Authors

Dr. Kenneth D. Frederick
Kenneth (Ken) Frederick is a senior fellow in Resources for the Future's (RFF) Energy and Natural Resources division. He has been a member of the research staff since 1971. His recent research and writings have addressed the economic, environmental, and institutional aspects of water resource use and management and the potential impacts of an anthropogenically-induced climate change on the supply and demand for water. He is the author, co-author, or editor of eight books.

Before joining RFF, Ken served as an economic advisor in Brazil for the U.S. Agency for International Development (1965-67) and as an assistant professor of economics at the California Institute of Technology (1967-71). He is a former member of the National Research Council's Water Science and Technology Board. He has served as vice chair of the board's committee on the Future of Irrigation in the Face of Competing Demands and as a member of their committee on Climate Change and Water Resources Management. He has also served as a consultant to federal agencies, international lending institutions, the government of Argentina, and private corporations.

Dr. Peter Gleick
Peter H. Gleick is co-founder and President of the Pacific Institute for Studies in Development, Environment, and Security. He is a leading expert on global freshwater resources, including sustainable use of water, the hydrologic impacts of climate change, demand management and water-use efficiency concepts, regional and international water conflicts, water planning and management, and the connections between water, population, and development. Dr. Gleick received a MacArthur Foundation Research and Writing Fellowship in 1988 to explore the implications of global environmental changes for water and international security. He is the author of Water in Crisis (Oxford University Press, 1993) and The World's Water 1998-1999 (Island Press, 1998) as well as numerous scientific papers.

Kenneth D. Frederick
Peter H. Gleick
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Press Release: Study Finds Climate Change Will Impact U.S. Water Supply

For Immediate Release:
September 27, 1999

Contact: Kelly Sullivan/Heather Fass
             202-289-5900

Study Finds Climate Change Will Impact U.S. Water Supply: Both Quantity and Quality of Water Supply Could Be Affected

WASHINGTON, D.C. -- A new study released today by the Pew Center on Global Climate Change concludes that climate change is likely to impact both the availability and quality of the U.S. water supply.

The study, Water Resources and Global Climate Change, finds that as climate change alters precipitation, evapotranspiration and runoff in the United States, these changes are likely to affect the magnitude, frequency, and costs of extreme weather events, as well as our nation's water supply.

The report, one in a series by the Pew Center examining the impacts of climate change on the environment, was researched and written by Dr. Kenneth Frederick of Resources for the Future, and Dr. Peter Gleick of Pacific Institute for Studies in Development, Environment & Security.

"Recent floods and droughts have reminded everyone that the climate and our nation's water supply are inextricably linked," said Eileen Claussen, Executive Director, Pew Center on Global Climate Change. "This study shows that as the climate changes, so will its impact on our water supply."

While some specifics are difficult to predict, several consistent impacts can be identified. For example, in mountainous watersheds, higher temperatures will increase the ratio of rain to snow, accelerate the rate of spring snowmelt, and shorten the overall snowfall season, leading to more rapid, earlier, and greater spring runoff.

In already arid regions, there is likely to be greater flux in the water supply, while higher temperatures fuel an increased demand for water. In other areas, new instances of flooding and droughts also will impact the availability of water.

"An adequate - and safe - water supply is an essential component to our health, environment, communities and economy," said Claussen. "These new findings demonstrate that climate change will not only impact the quantity of our water supply, but the quality as well."

While higher water flows could improve water quality in some streams, the increased runoff of pollutants and saltwater intrusion could accompany climate change induced sea-level rise.

The study notes that there are steps that can be taken today to begin preparing for changes in our water supply. In addition to reviewing options for adapting and expanding the existing infrastructure, including reservoirs and dams, there are opportunities to develop water marketing and trading strategies and improve the management of water systems.

"The findings from this report show without question that there are steps we can - and should - be taking today to prepare our water supply for the consequences of climate change," said Claussen. "But the most important step of all is to reduce the greenhouse gas emissions that cause climate change."

In addition to being presented to Members of Congress and their staff at a briefing tomorrow on Capitol Hill, the findings from the study also are highlighted in a print advertisement sponsored by the Pew Center. The advertisement is scheduled to run on September 29th in The Washington Post, September 30th in Roll Call, and October 2nd in National Journal.

The Pew Center was established in May 1998 by the Pew Charitable Trusts, one of the nation's largest philanthropies and an influential voice in efforts to improve the quality of America's environment. The Pew Center supports businesses in developing marketplace solutions to reduce greenhouse gases, produces analytical reports on the science, economics and policies related to climate change, launches public education efforts, and promotes better understanding of market mechanisms globally. Eileen Claussen, former U.S. Assistant Secretary of State for Oceans and International Environmental and Scientific Affairs, is the executive director of the Pew Center.

The Pew Center includes the Business Environmental Leadership Council, which is composed of 21 major, largely Fortune 500 corporations all working with the Pew Center to address issues related to climate change. The companies do not contribute financially to the Pew Center - it is solely supported by contributions from charitable foundations.

Press Release: Report Details New Information on Climate Change Impacts

For Immediate Release:
June 29, 1999

Contact: Kelly Sullivan/Heather Fass
             202-289-5900

Report Details New Information on Climate Change: Including Impacts on Temperature, Sea Level, Precipitation and Extreme Weather Events

U.S. Specific Information Included

WASHINGTON, D.C. - The Pew Center on Global Climate Change will release a new report, which examines the science of climate change. The news conference is scheduled for Tuesday, June 29 at 10:00 am in the Zenger Room, National Press Club.

The analysis is based on the most recent data from preliminary versions of four new emissions scenarios identified by the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES).

The Pew Center was established in May 1998 by the Pew Charitable Trusts, one of the nation's largest philanthropies and an influential voice in efforts to improve the quality of America's environment. The Pew Center is conducting studies, launching public education efforts, promoting climate change solutions globally and working with businesses to develop marketplace solutions to reduce greenhouse gases. The Pew Center includes the Business Environmental Leadership Council, which is composed of 21 major, largely Fortune 500, corporations. The companies do not contribute financially to the Pew Center. The Pew Center is led by Eileen Claussen the former U.S. Assistant Secretary of State for Oceans and International Environmental and Scientific Affairs.

WHAT: - Pew Center on Global Climate Change to release report, "The Science of Climate Change: Global and U.S. Perspectives"

WHO: - Tom M.L. Wigley, National Center for Atmospheric Research and author of the report - Eileen Claussen, Executive Director, Pew Center on Global Climate Change

WHEN: - Tuesday, June 29, 1999 at 10:00 am

WHERE: - Zenger Room, National Press Club, 529 14th Street, NW

Press Release: New Study Shows Higher Rate of Warming and Sea Level Rise Than Previously Expected

For Immediate Release:
June 29, 1999

Contact: Kelly Sullivan/Heather Fass
             202-289-5900

New Study Shows Higher Rate of Warming and Sea Level Rise Than Previously Expected: U.S. Temperature Rise Expected to be Greater Than Global Average

WASHINGTON, D.C. — A new report released by the Pew Center on Global Climate Change reveals slightly higher rates of warming and sea level rise than predicted in 1995 by an international group of scientists on the Intergovernmental Panel on Climate Change (IPCC). The new estimates are based on preliminary versions of four new emissions scenarios identified by the IPCC Special Report on Emissions Scenarios (SRES).

The projected changes are 1.3 - 4.0°C (2.3 - 7.2°F) for global-mean temperature (previous IPCC projections were 0.8 - 3.5°C; 1.4 - 6.3°F), and 17 to 99 cm. (7 to 39 in.) for sea level rise by 2100 (versus 13 to 94 cm.; 5 to 37 in. from the IPCC). These high projected increases in temperature and sea level rise are due to lower levels of sulfur dioxide emissions than previous projections (efforts to reduce sulfur dioxide - another pollutant - could result in increased warming since sulfate particles cool the atmosphere).

For temperature, these values mean that future changes in global-mean temperatures will be 2 to 7 times more rapid than those of the 20th century and that rises in sea level will occur at rates 1 to 7 times those of the 20th century.

"As policymakers, industry and the public tackle the challenges of climate change, understanding the seriousness and complexity of the issue is critical to crafting the most effective responses," said Eileen Claussen, Executive Director, Pew Center on Global Climate Change. "The data and likely impacts outlined in this study should encourage concrete steps to reduce greenhouse gas emissions."

The study, "The Science of Climate Change: Global and U.S. Perspectives," was conducted and written by Tom M.L. Wigley of the National Center for Atmospheric Research for the Pew Center on Global Climate Change.

Based on results from a number of climate models, the rate of future warming for the United States is expected to be noticeably faster than the global-mean rate. While the Southeast and Southwest tend to show warming slightly below the global-mean, the northernmost states from North Dakota eastward to Maine show enhanced warming by a factor of up to two during the winter months. Future regional-scale precipitation changes are highly uncertain. The only result that is common to all climate models is an increase in winter precipitation in northern latitudes, from the northern Great Plains to the northeastern states.

The study also found that changes in climate extremes were likely.

  • Warm temperature extremes will almost certainly become more frequent;
  • Cold temperature extremes will almost certainly become less frequent;
  • The frequency of high precipitation events is likely to increase;
  • It is likely that rainfall amounts associated with hurricanes will increase; and
  • An increase in the frequency and intensity of hurricanes in the North Atlantic region is possible.

F or all extreme events, however, it is unlikely that the projected changes will become evident in a statistically convincing way for many decades, with the exception of temperature extremes, which should become evident sooner.

This most recent research also strengthens the IPCC statement that "the balance of evidence suggests a discernible human influence on global climate." First, climate model estimates of global-mean temperature changes over the 20th Century, and of the patterns of temperature change, are consistent with observations. Second, the effects of solar changes on the climate have been better quantified. They show that the sun can only account for about one-third of the observed global-mean warming. Third, scientists are beginning to understand why recent trends in the temperature of the lower to mid-troposphere derived from satellite data differ from those at the surface.

"This research provides valuable information that should move the climate change debate beyond questions about the science and towards realistic solutions," said Claussen.

The findings in the study will be highlighted in a print advertisement supported by the Pew Center, which is scheduled to appear in The New York Times, The Washington Post, National Journal, Roll Call and Newsweek.

The Pew Center was established in May 1998 by the Pew Charitable Trusts, one of the nation's largest philanthropies and an influential voice in efforts to improve the quality of America's environment. The Pew Center is conducting studies, launching public education efforts, promoting climate change solutions globally and working with businesses to develop marketplace solutions to reduce greenhouse gases. The Pew Center is led by Eileen Claussen the former U.S. Assistant Secretary of State for Oceans and International Environmental and Scientific Affairs.

The Pew Center includes the Business Environmental Leadership Council, which is composed of 21 major, largely Fortune 500 corporations all working with the Pew Center to address issues related to climate change. The companies do not contribute financially to the Pew Center - it is solely supported by contributions from charitable foundations.

Agriculture & Global Climate Change: A Review of Impacts to U.S. Agricultural Resources

Agriculture & Global Climate Change: A Review of Impacts to U.S. Agricultural Resources

Prepared for the Pew Center on Global Climate Change
February 1999

By:
Richard M. Adams, Oregon State University
Brian H. Hurd, Stratus Consulting Inc.
John Reilly, Massachusetts Institute of Technology

Press Release

Download Entire Report (pdf)

Foreword

Eileen Claussen, Executive Director, Pew Center on Global Climate Change

In order to intelligently respond to climate change, we must first understand the likely consequences on our environment and health. This report, the first in a series of environmental impact reports, will explore anticipated effects of climate change on U.S. agriculture. Other reports in this series will assess what is known about the impact of climate change on weather and include analyses of its impact on water resources, coastal areas, human health, ecosystems, and forests. In evaluating the current state of scientific knowledge regarding the anticipated effects of climate change on U.S. agriculture, this report yields several key observations:

AGRICULTURAL SHIFTS ARE LIKELY.
Climate change will result in agricultural shifts and changes across the United States. Given the requisite time and resources to adapt, the United States is likely to continue to be able to feed itself; however, there will clearly be regional winners and losers.

CURRENT PROJECTION SCOULD UNDERSTATE LONG-RANGE IMPACTS.
If the rate of greenhouse gas emissions exceeds projected levels or if unanticipated or more frequent extreme events accompany this change, the outlook for the United States would likely worsen. The projections in this report, for example, are based on a doubling of carbon dioxide (CO2) in the atmosphere which could understate the severity of climate change impacts over the long-term.

GLOBAL IMPACTS COULD BE MORE PROFOUND.
Some countries will experience more negative effects on agriculture associated with climate change. The situation will be particularly acute in developing nations that do not have the same resources as the United States to respond to the agricultural changes projected.

This report broadly outlines projected effects on U.S. agricultural regions. The complexity of the climate system itself and its relationship to agricultural resources make it difficult to project specific effects on individual states or communities. More research is needed to better understand this complex system and to incorporate relevant factors into future climate models and assessments. The report does, however, provide an objective foundation upon which to build and clearly demonstrates the impact climate change will have, both direct and indirect, on U.S. agricultural systems.

In addition to reporting on the environmental impacts of climate change, the Pew Center undertakes analyses on domestic and international policy matters and economics. The Center was established in 1998 by the Pew Charitable Trusts to bring a new, cooperative approach and critical scientific, economic and technological expertise to the global climate change debate.

A number of major corporations have taken a bold and historic step in joining the Center's Business Environmental Leadership Council. In doing so, they have accepted "the views of most scientists that enough is known about the science and environmental impacts of climate change for us to take actions to address its consequences." Understanding the potential environmental impacts of climate change, as this report illustrates, is an important step toward promoting informed action.

Executive Summary

This paper analyzes the current state of knowledge about the effects of climate change on U.S. food production and agricultural resources. The paper also considers regional changes in agricultural production, including distributional impacts.

The linkages between agriculture and climate are pronounced, often complex, and not always well understood. Temperature increases can have both positive and negative effects on crop yields, with the difference depending in part on location and on the magnitude of the increase. Crop yields in the northern United States and Canada may increase, but yields in the already warm, low-latitude regions of the southern United States are likely to decline. Evidence also suggests positive crop yield effects for mild to moderate temperature increases such as 2°C to 3°C (3.6°F to 5.4°F). However, once average global temperatures rise beyond about 4°C (7.2°F), yields begin to fall. Increases in precipitation level, timing, and variability may benefit semi-arid and other water-short areas by increasing soil moisture, but could aggravate problems in regions with excess water. Although most climate models predict precipitation increases, some regions will experience decreased precipitation, which could exacerbate water shortages and droughts. Higher carbon dioxide (CO2) levels in controlled experiments increase crop growth and decrease water use. However, these experiments often have demonstrated a more positive response than observed under actual field conditions.

Agricultural systems are most sensitive to extreme climatic events such as floods, wind storms, and droughts, and to seasonal variability such as periods of frost, cold temperatures, and changing rainfall patterns. Climate change could alter the frequency and magnitude of extreme events and could change seasonal patterns in both favorable and unfavorable ways, depending on regional conditions. Increases in rainfall intensity pose a threat to agriculture and the environment because heavy rainfall is primarily responsible for soil erosion, leaching of agricultural chemicals, and run off that carries livestock waste and nutrients into water bodies. Currently available climate forecasts cannot resolve how extreme events and variability will change; however, both are potential risks to agriculture. The rate of change is also uncertain. Adjustment costs are likely to be higher with greater rates of change.

Agricultural systems are managed. Farmers have a number of adaptation options open to them, such as changing planting and harvest dates, rotating crops, selecting crops and crop varieties for cultivation, consuming water for irrigation, using fertilizers, and choosing tillage practices. These adaptation strategies can lessen potential yield losses from climate change and improve yields in regions where climate change has beneficial effects. At the market level, price and other changes can signal further opportunities to adapt as farmers make decisions about land use and which crops to grow. Thus, patterns of food production respond not only to biophysical changes in crop and livestock productivity brought about by climate change or technological change, but also to changes in agricultural management practices, crop and livestock prices, the cost and availability of inputs, and government policies. In the longer term, adaptations include the development and use of new crop varieties that offer advantages under changed climates, or investments in new irrigation infrastructure as insurance against potentially less reliable rainfall. The extent to which opportunities for adaptation are realized depends upon a variety of factors such as information flow, access to capital, and the flexibility of government programs and policies.

Climate change can also have a number of negative indirect effects on agro-environmental systems effects that have been largely ignored in climate change assessments. These indirect effects include changes in the incidence and distribution of pests and pathogens, increased rates of soil erosion and degradation, and increased tropospheric ozone levels from rising temperatures. Regional shifts in crop production and expansion of irrigated acreage may stress environmental and natural resources, including water quantity and quality, wetlands, soil, fish, and wildlife.

The focus of this paper is on the impacts of climate change on agriculture. However, agriculture is also a potential source of greenhouse gas (GHG) emissions, and it can play an important role in mitigating these emissions. Methane from rice paddies and livestock, nitrous oxide (N2O) from cultivated soils and feedlots, and CO2 from the cultivation of virgin agricultural lands and intensive production methods contribute to global warming. Changes in management can reduce emissions from these sources. Agriculture can reduce atmospheric CO2 through tree-planting and similar programs that sequester significant amounts of carbon and through increased planting of biofuel crops that could replace fossil fuels.

The following describes the current understanding regarding the potential impacts of climate change on U.S. agriculture:

CROPS AND LIVESTOCK ARE SENSITIVE TO CLIMATE CHANGES IN BOTH POSITIVE AND NEGATIVE WAYS. Understanding the direct biophysical and economic responses to these changes is complicated and requires more research. In addition, indirect effects - such as changes in pests and water quality and changes in extreme climate events - are not well understood.

THE EMERGING CONSENSUS FROM MODELING STUDIES IS THAT THE NET EFFECTS ON U.S. AGRICULTURE ASSOCIATED WITH ADOUBLING OF CO2 MAY BE SMALL; HOWEVER, REGIONAL CHANGES MAY BE SIGNIFICANT (I.E., THERE WILL BE SOME REGIONS THAT GAIN AND OTHERS THAT LOSE). Beyond a doubling of CO2 , the negative effects are more pronounced both in the United States and globally.

THE IMPACT OF CLIMATE CHANGE ON U.S. AGRICULTURE IS MIXED. Climate change is not expected to threaten the ability of the United States to produce enough food to feed itself through the next century; however, regional patterns of production are likely to change. Regions such as the Northern Great Plains and Great Lakes may have increased productivity while the Southern Plains, Delta states, and possibly the Southeast and portions of the Corn Belt could see agricultural productivity fall. However, the form and pattern of change are uncertain because changes in regional climate cannot be predicted with a high degree of confidence.

CONSIDERATION OF ADAPTATION AND HUMAN RESPONSE IS CRITICAL TO THE ACCURATE AND CREDIBLE ASSESSMENT OF CLIMATE CHANGE IMPACTS.However, because of the long time horizons involved in climate change assessments and uncertainties concerning the rate at which climate will change, it is difficult to predict accurately what adaptations people will make. This is particularly challenging since adaptations are influenced by many factors, including government policy, prices, technology research and development, and agricultural extension services.

BETTER CLIMATE CHANGE FORECASTS ARE KEY TO IMPROVE DASSESSMENTS OF THE IMPACTS OF CLIMATE CHANGE. In the meantime, farmers and the agricultural community must consider strategies that are economically and environmentally viable in the face of uncertainty about the course of climate change.

AGRICULTURE IS A SECTOR THAT CAN ADAPT, BUT THERE ARE SOME FACTORS NOT INCLUDED IN ASSESSMENTS THAT COULD CHANGE THIS CONCLUSION.Changes in the incidence and severity of agricultural pests, diseases, soil erosion, and tropospheric ozone levels, as well as changes in extreme events such as droughts and floods, are largely unmeasured or uncertain and have not been incorporated into estimates of impacts. These omitted effects could result in a very different assessment of the true impacts of climate change on agriculture. If the rate or magnitude of climate change is much greater than anticipated, adaptation could be more difficult and impacts could be greater than currently expected.
Overall, the consensus of economic assessments is that global climate change of the magnitudes currently being discussed by the Intergovernmental Panel on Climate Change (IPCC) and other organizations (i.e., +0.8°C to +4.5°C or +1.4°F to +8.1°F) could result in some lowering of global production but will have only a small overall effect on U.S. agriculture and its ability to provide sufficient food and fiber to both domestic and global customers over the next 100 years. However, distributional effects within the United States can be significant because consumers, producers, and local economies will gain in some regions and lose in others.

Warming beyond that reflected in current studies (i.e., associated with a continued rise in CO2 beyond the doubling that has been commonly investigated) is expected to impose greater costs, decreasing agricultural production in most areas of the United States and substantially limiting global production. This reinforces the need to determine the magnitude and rate of warming that may accompany the CO2 and greenhouse gas build-up currently underway in the atmosphere.

About the Authors

Richard M. Adams
Oregon State University, Corvallis, OR

Richard M. Adams received his Ph.D. in Agricultural Economics from the University of California, Davis, in 1975. He is currently a professor of Agricultural and Resource Economics at Oregon State University, a position he has held since 1983. His research interests include the economic analysis of resource and environmental issues, with emphasis on the consequences of environmental change. Professor Adams has served on numerous governmental advisory and research committees dealing with environmental issues. He has published over 160 journal articles, book chapters and research reports, including 20 on the effects of climate change on agriculture and agricultural resources. He has served on the editorial boards of five journals and w as editor of the American Journal of Agricultural Economics from 1992 to 1994.

Brian H. Hurd
Stratus Consulting Inc., Boulder, CO

Brian H. Hurd is a Senior Associate in the climate change group at Stratus Consulting, a Boulder-based environment and energy research firm. He received his Ph.D. in agricultural economics from the University of California, Davis in 1992, where he analyzed technology changes in production agriculture. His passion for interdisciplinary research and for contributing to public decision-making regarding natural resources has led to his current focus on climate change. He has developed regional and national models of water resource impacts, analyzed land use changes in forestry and agriculture, and investigated adaptation and mitigation strategies, while serving a variety of public- and private-sector clients such as U.S. EPA, U.S. Department of Energy, National Science Foundation, National Institute for Global Environmental Change, and the Electric Power Research Institute.

John Reilly
Massachusetts Institute of Technology, Cambridge, MA

Dr. Reilly is the Associate Director for Research in the Joint Program on the Science and Policy of Global Change at the Massachusetts Institute of Technology. He spent 12 years with the Economic Research Service of USDA, most recently as the Acting Director and Deputy Director for Research of the Resource Economics Division. He has been a scientist with Battelle's Pacific Northwest National Laboratory and with the Institute for Energy Analysis, Oak Ridge Associated Universities. He received his Ph.D. in economics from the University of Pennsylvania in 1983 and holds a BS in economics and political science from the University of Wisconsin. He has conducted research on the economics of climate change for 19 years. He was a principal author for the Intergovernmental Panel on Climate Change's Second Assessment Report and has served on many Federal government and international committees on climate change and agricultural research.

 

 

Brian Hurd
John M. Reilly
Richard M. Adams
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Press Release: New Study Details Effects of Climate Change On U.S. Agriculture

For Immediate Release:
February 10, 1999

Contact: Shannon Hunt / Kelly Sullivan
             (202) 289-5900

New Study Details Effects of Climate Change On U.S. Agriculture

Projected Regional Impacts on Agriculture Outlined: New Report is First in Series Examining Environmental Impacts of Climate Change

WASHINGTON, D.C. — Climate change has the potential to affect livestock and crops, local agricultural economies and crop production trends according to a new report by the Pew Center on Global Climate Change, which examines the effects of climate change on agriculture. The report finds that while climate change is not expected to threaten the ability of the U.S. to produce enough food to feed itself through the next century, some U.S. agricultural regions, particularly in the north, are expected to benefit, while others, primarily in the south, could face adverse impacts.

The report, released today at a press conference on Capitol Hill, notes that the resiliency and adaptability of the U.S. agricultural sector has made it one of the country's most productive industries and gives the sector the ability to adapt to the changes associated with climate change. However, the report also finds that there remains a potential for negative effects, and particular regions, especially those in the south, will face greater obstacles in adapting to the challenges posed by climate change.

"Anyone with a stake in agriculture should be interested in the findings of this report, which shows that the farming industry we know today will not be the same in the future under the effects of climate change," said Eileen Claussen, Pew Center Executive Director.

At Wednesday's press conference, Agriculture Committee Chairman Richard Lugar (R-IN) and Senator Bob Kerrey (D-NE) both issued statements supporting the Pew Center's efforts to inform American agricultural producers about the potential impacts of climate change.

According to the report, climate change could cause grain yields to fall significantly in southern states, while in the north, longer growing seasons could increase yields of grains such as wheat. Changes in grain production and foraging regions could also cause shifts in the locations of livestock production. Uncertainty in the models does not allow precision in identifying localized effects.

The study finds that in order to develop the most accurate and credible assessment of the possible impacts of climate change, it is important to consider adaptation and human response, as well as to continue to develop improved climate change forecasts. But, given the potential impacts, farmers and the agricultural community must consider new strategies in the face of uncertainty.

The report states that the emerging consensus from modeling studies is that the net effects on U.S. agriculture, with a doubling of carbon dioxide in the atmosphere, may be small. But, these models may understate long-range impacts if the rate or magnitude of greenhouse gas emissions exceed projected levels. For example, extreme events - such as storms, droughts and early and late frosts caused by climate change - also could play a role in determining the ultimate impact of climate change on agriculture.

Additionally, secondary impacts of climate change, such as the potential for higher ozone levels, impacts on water resources and pest populations, contribute to the uncertainty and pose additional challenges not only to individual producers, but also larger agricultural economies.

The value of U.S. agricultural commodities exceeds $165 billion at the farm level and over $500 billion after processing and marketing. "The role of the U.S. agricultural sector is too important for us to ignore these findings," said Claussen. "The agricultural community can adapt to climate change, but adaptation takes time and resources, and with uncertainties related to the timing and magnitude of temperature changes, not all opportunities for adaptation are likely to be realized."

This report is the first in a series of environmental impact reports slated to be released by the Pew Center this year. Other reports in this series will assess what is known about the impact of climate change on weather and includes analyses of its impact on water resources, coastal areas, human health, ecosystems, and forests.

A copy of the report, "A Review of Impacts to U.S. Agricultural Resources," is available on the Pew Center web site at www.c2es.org.

The Pew Center was established in May 1998 by the Pew Charitable Trusts, one of the nation's largest philanthropies and an influential voice in efforts to improve the quality of America's environment. The Pew Center is conducting studies, launching public education efforts, promoting climate change solutions globally and working with businesses to develop marketplace solutions to reduce greenhouse gases. The Pew Center is led by Eileen Claussen the former U.S. Assistant Secretary of State for Oceans and International Environmental and Scientific Affairs.

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