How the West Will Warm
In the arid American West, unchecked global warming will hurt the water supply, the economy and the environment -- but concrete action can help mitigate these effects.

Back to the Global Warming in the West Index

Global average temperatures have increased by 1.1 degrees Fahrenheit over the last century
-- warming faster than any time in the last 1000 years. The vast majority of mainstream scientists agree that these rising temperatures are caused by carbon dioxide and other heat-trapping gases produced from the burning of fossil fuels in cars and power plants.

The arid American West appears to be particularly susceptible to the effects of global warming. Over the past 50 years, the western climate has warmed on average by 1.4 degrees Fahrenheit, and climate models predict a further increase of 3.6 to 12.6 degrees Fahrenheit in the West by the end of the century. A growing body of scientific evidence is linking global warming trends with changes in precipitation, declining snowpack, and smaller and earlier spring runoff -- conditions that determine the quantity and timing of water supplies in the West, as well as wildfire risk. Many parts of the West are already experiencing devastating multi-year droughts. If current global warming trends continue, they present serious consequences to many bedrock elements of western life, from agriculture and ranching to skiing, tourism, biodiversity and public health.

Without taking immediate steps to reduce global warming pollution, the economic, hydrologic and environmental impacts of global warming in the West could be catastrophic.

Decreased Water Supplies

Global warming may not only be exacerbating the current drought in much of the West, but may cause similar drought-like conditions in the future. Snowpack, which acts as temporary water storage, provides up to 75 percent of the region's annual water supply.1 Additional increases in global temperatures will decrease snowpack in the West by as much as 40 percent by 2060.2 The loss of snowpack will decrease the total water supply both locally and regionally, making summers drier and droughts worse. Further reduced water supplies will exacerbate existing conflicts as well as generate new urban, agricultural and natural resource-related problems.

In the Colorado River Basin, for example, high elevation snow pack contributes approximately 70 percent of the annual runoff.3 With global warming predicted to result in an estimated 24 percent decrease in snowpack over the next 35 years,4 the current drought conditions in the Southwest could become the norm. The largest impacts may be felt in the Upper Basin states of Wyoming, Utah, Colorado and New Mexico, as the Colorado River Compact prioritizes the delivery of water to the Lower Basin states of Arizona, California and Nevada. However, it is estimated that with increased global warming the compact requirements may only be met 59 to 75 percent of the time.5

In California, global warming puts the drinking water supply for 22 million people at risk. Every year, a delicate balance must be maintained in the San Francisco Bay-Delta Estuary between fresh water inflows from Sierra Nevada rivers and salt water intrusion from the Pacific Ocean. Decreased river flows resulting from reduced snow packs and earlier snow melts may result in higher spring-summer salinities in the Delta.6 The frail levee system throughout the Delta is already vulnerable to failures, which could produce massive inflows of salty sea water and taint water supplies. Without action, the risk to California's primary water supply will increase as sea levels continue to rise by as much as 2 to 3 feet over the next 100 years.7

Decreased Hydropower Production

Reduced snowpack and early snowmelt runoff will also reduce hydropower production. Studies have shown that a 10 percent decrease in flows can result in a 36 percent reduction in power production.8 Within the Columbia River basin, projected reductions in snowpack runoff combined with meeting other water demands could reduce hydropower production by as much as 20 percent by 2060.9 In the Colorado River basin, decreased river runoff could reduce hydropower output by 50 percent.10 In streams throughout California's Sierra Nevada, spring runoff is occurring as much as three weeks earlier than in 1948.11 Early snowmelt exacerbates the problem by reducing the flows that would normally be available later in the spring and summer, when electricity demand is greater.

Increased Flooding

As the climate warms, more precipitation will fall as rain instead of snow, thereby increasing the frequency and magnitude of flooding on lands adjacent to rivers (floodplains). Such an increase in flooding would not only affect public safety, but also the economy and water supply. In California, 50 percent of all federally declared disasters are related to floods -- more than wildfires and earthquakes combined.12 In order to provide public protection against flooding, the operation of many dams in the West may need to be changed to keep more of the existing storage capacity empty for flood reserves, thereby reducing the dam's ability to capture and provide water supplies.

Reduced Agricultural Production

Decreased crop yields and reduced water supplies resulting from global warming have the potential to seriously affect the local and regional agricultural economies in the West. Studies in the last year have concluded that increasing temperatures negatively affected crop yields for rice, soybeans and corn.13 The Intergovernmental Panel on Climate Change states that global warming may cause corn yields to drop by 15 to 30 percent across the United States.14 Similarly, the U.S. Environmental Protection Agency (EPA) estimates that as temperatures near the upper tolerance levels for wheat, crop yields will drop 10 to 30 percent in New Mexico and Utah, approximately 48 to 66 percent in California, and up to 70 percent in Arizona.15

Loss of Wildlife Habitat

The increase in global temperatures will disrupt ecosystems around the world. One analysis revealed that more than 1 million species, unable to adapt to the warming climate, could be committed to extinction by 2050 if global warming pollution is not curtailed.16 Aquatic species such as trout and salmon will likely experience a significant reduction or disappear entirely from some rivers and streams due to increased stream temperatures and reduced flows.17 The result of continued global warming will likely be a proliferation of crises in the West, like those seen with the silvery minnow in New Mexico and with salmon on the Klamath River in California and Oregon.18 Without efforts to reduce global warming and prepare for its impacts, resource managers will increasingly struggle to respond to declining fish and wildlife populations and increased pressure on existing water supplies.

Economic Losses for the Recreation Industry

Global warming is a bottom-line issue for the $3 billion-a-year ski industry in the United States. Climate experts say that without action soon, western ski regions will see less snow and shorter, more erratic seasons.19 Similar effects will be felt in the recreational fishing industry. In 1996, an estimated 9 million trout anglers in the United States spent some 94 million person-days fishing, generating somewhere between $900 million and $14 billion in revenue.20 An analysis of global warming impacts on trout habitat predicts that up to 42 percent of existing habitat in the West could be lost by 2090. The impact of global warming on recreational industries and related businesses could be measured in the tens of billions.


Unchecked, global warming will harm the economy, public health and environment in the Western states. Taking the following steps now to conserve natural resources and decrease emissions of global warming pollution will help mitigate these effects:

  • Educating decision-makers and the public about the impacts of global warming and ways to cut global warming pollution will help prompt them take action. The National Ski Areas Association has set an example by participating in awareness campaigns and lobbying decision-makers to support legislation to reduce global warming pollution by promoting cleaner and more efficient vehicles and cleaner means of power production, such as wind and solar power.

  • Conserving and reclaiming water are the most timely and cost-effective water supply solutions. Increased conservation and water use efficiency by urban and agricultural water users will maximize existing supplies. Wastewater reclamation creates new water supply while reducing water quality problems caused by waste discharge.

  • Expanding the use of floodplains as part of an integrated flood management strategy will enable existing dams to maximize water supply and hydropower production rather than be re-operated to provide more flood protection. Dedicating floodplains to uses that are more compatible with flooding, such as parks and agriculture, will increase public safety, conserve natural and agricultural lands, increase groundwater recharge and improve water quality.

  • Addressing climate change impacts in resource management planning will reduce endangered species conflicts and help wildlife to adapt climate change. Protecting and restoring wildlife corridors, refuges and higher elevation habitats will help minimize the impacts of global warming on wildlife.

Further Resources

Barnett, T., Malone, R., Pennell, W., Stammer, D., Semtner, B. and Washington, W., "The Effects of Climate Change on Water Resources in the West: Introduction and Overview," Climatic Change 62 (1-3) (2004): p. 1-11.

Christensen, N.S., Wood, A.W., Voisin, N., Lettenmaier, D.P. and Palmer, R.N., "The Effects of Climate Change on the Hydrology and Water Resources of the Colorado River Basin," Climatic Change 62 (1-3) (2004): p. 337-363.

Knowles, N. and Cayan, D.R., "Elevational Dependence of Projected Hydrologic Changes in the San Francisco Estuary and Watershed," Climatic Change 62 (1-3) (2004): p. 319-336.

Mote, P. W., "Trends in Snow Water Equivalent in the Pacific Northwest and Their Climatic Causes," Geophysical Research Letters 30(12) 1601(2003).

Payne, J.T., Wood, A.W., Hamlet, A.F., Palmer, R.N., and Lettenmaier, D.P., "Mitigating the Effects of Climate Change on the Water Resources of the Columbia River Basin," Climatic Change 62 (1-3) (2004), p. 234-256.

Service, R.F., "As the West Goes Dry," Science , Volume 303 (2004): p.1124-1127.

last revised 12.9.04


1. Ibid.

2. Mote, P. W. May 6, 2004. The West's Snow Resources in a Changing Climate - Testimony before the U.S. Senate Committee on Commerce, Science, and Transportation.

3. Christensen, N.S., Wood A.W., Voisin, N., Lettenmaier, D.P. and Palmer, R.N. 2004. The effects of climate change on the hydrology and water resources of the Colorado River Basin. Climatic Change 62 (1-3), p. 337-363.

4. Ibid.

5. Ibid.

6. Knowles, N. and Cayan, D.R. 2004. Elevational dependence of projected hydrologic changes in the San Francisco estuary and watershed. Climatic Change 62 (1-3), p. 319-336.

7. Sea level rise and coastal flooding. Union of Concerned Scientists.

8. EPA's Global Warming website under the header Hydropower -

9. Payne, J.T., Wood, A.W., Hamlet, A.F., Palmer, R.N. and Lettermaier D.P. 2004. Mitigating the effects of climate change on the water resources of the Columbia River Basin. Climatic Change 62 (1-3), p. 234-256.

10. Ibid.

11. Service, R.F. 2004. As the west goes dry. Science, vol. 303, p. 1124-1127.

12. Ibid.

13. Schmid, Randolph E. (AP), June 28, 2004. Global warming hurts rice yields.

14. Service, R.F. 2004. As the west goes dry. Science, vol. 303, p. 1124-1127.

15. EPA Climate Change Sheets on individual states found at:

16. Chris D. Thomas, Alison Cameron, Rhys E. Green, Michel Bakkenes, Linda J. Beaumont, Yvonne C. Collingham, Barend F. N. Erasmus, Marinez Ferreira de Siqueira, Alan Grainger, Lee Hannah, Lesley Hughes, Brian Huntley, Albert S. van Jaarsveld, Guy F. Midgley, Lera Miles, Miguel A. Ortega-Huerta, A. Townsend Peterson, Oliver L. Phillips, Stephen E. Williams Extinction Risk from Climate Change, Nature 427, 145 - 148 (08 Jan 2004) Letters to Nature.

17. Defenders of Wildlife, 2002. Effects of Global Warming on Trout and Salmon in U.S. Streams.

18. Ibid.


20. Defenders of Wildlife, 2002. Effects of Global Warming on Trout and Salmon in U.S. Streams.

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