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Climate Change Impacts

Climate Impacts in the Southwest

On This Page:

Overview

Water Resources

Native Americans

Human Health

Forests and Ecosystems

Agriculture

Key Points

Warming temperatures and reduced snowpack have been observed in recent decades in the Southwest.

Increasing temperatures and more frequent and severe droughts are expected to heighten competition for water resources for use in cities, agriculture, and energy production.

Native communities are expected to experience more difficulties associated with access to freshwater, agricultural practices, and declines in medicinal and cultural plants and animals.

Drought, wildfire, invasive species, pests, and changes in species' geographic ranges will increase threats to native forests and ecosystems.

Related Links

EPA:

EPA Region 6 (including the Southwest states of NM and TX)

EPA Region 8 (including the Southwest states of CO and UT)

EPA Region 9 (including the Southwest states of AZ, CA, and NV)

EPA Climate Change Indicators, Temperature and Drought in the Southwest

Other:

IPCC Working Group II : North America Exit

USGCRP, Global Climate Change Impacts in the United States: Southwest

Climate Assessment for the Southwest: University of Arizona Exit

U.S. Fish and Wildlife Service: Climate Change in the Pacific Southwest

ITEP, Tribes & Climate Change Exit

Overview

The Southwest is the hottest and driest region in the nation.[1] Extending from the Pacific Ocean east to the Rocky Mountains and south to the Mexican border, this region is home to about 56 million people, about 90% of whom live in cities, including Albuquerque, Phoenix, Las Vegas, Salt Lake City, Denver, San Diego, Los Angeles, Sacramento, and San Francisco. The population of the Southwest is expected to increase by nearly 70% by mid-century.[1] The Southwest encompasses a wide range in elevations, spanning valleys that are below sea level to mountain ranges that contain some of the highest peaks in the contiguous United States. The region’s southern portion includes deserts, like the Mojave. In contrast, northern California, the Rocky Mountains, and the Sierra Nevada mountain range tend to get more precipitation and snow. The Central Valley in California is one of the most productive agricultural regions in the country.

Average temperatures across the entire Southwest have increased in recent years, with some areas increasing by up to 2°F. This map shows the average temperature from 2000-2013 relative to the long-term average from 1895-2013. Source: US EPA (2014)[8]

Climate change is affecting the Southwest. Temperatures have increased by almost 2°F in the last century, with the 2001-2010 decade being the warmest since records began 110 years ago.[1] The length of the frost-free season has increased by 19 days in recent decades.[2] Average annual temperatures are projected to rise an additional 3.5°F to 9.5°F by the end of this century, with the greatest temperature increases expected in the summer and fall.[1] Drought conditions are already common in the Southwest and drought periods are expected to become more frequent, intense, and longer. Drought will affect important water sources, including the Colorado River Basin.[1] Combined with expected population growth, climate change will exacerbate existing stresses.

Impacts on Water Resources

A reliable water supply is crucial for sustaining the people, agriculture, energy production, and ecosystems in this dry region. Increased water demand and reduced water supplies will add new stresses to already strained water resources.

The Southwest relies on the slow melt of mountain snowpack throughout the spring and summer, when water demands are highest. Snowpack helps keep the ground and soil moist by covering it longer into the spring and summer, which delays the onset of the fire season and influences the prevalence and severity of wildfires. Over the last 50 years, there has been less precipitation falling as snow late in the winter and snow melt has occurred earlier.[1]

Declines in snowpack, runoff, and soil moisture are projected to occur if greenhouse gas emissions remain high. The maps show the change in conditions between the historic (1971-2000) and the expected mid-century (2041-2070). Source: USGCRP (2014)[9]

Maximum streamflow has also occurred earlier in the year and total yearly streamflow has decreased in the last decade. In April 2015, California snowpack held only 5% of the water it typically holds at this time of year, with some areas having no snowpack.[3] This was the smallest April snowpack in the last 65 years, and projections indicate continued declines in snowpack in the Southwest in the future.[1] In addition to less snow accumulation, warmer temperatures are expected to speed snow melting, and rain falling on snow could result in more rapid runoff and flooding conditions in spring.[4]

Increasing temperatures will also increase evaporation, causing river-flow reductions and dwindling reservoirs. Rapid population growth will increase the competition for water resources across sectors, states, tribes, and even between the United States and Mexico.[1] Climate change will likely stress groundwater-based systems and result in decreased groundwater recharge.[4]

For more information on climate change impacts on water, please visit the Water Resources page.

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	Impacts on Native Americans

The Southwest is home to 182 federally recognized tribes and communities.[1] Native Americans already face many challenges that will be exacerbated by climate change. These communities face some of the highest poverty rates in the nation and often lack adequate food, infrastructure, transportation and access to health and community services.[5] Some communities, including the Navajo Nation, are already experiencing drought impacts. Some shallow wells have run dry and have reduced drinking water supplies. There have been reported losses of agricultural crops and livestock, as well as important medicinal and cultural plants and animals. As climate change impacts worsen, Native American populations will likely be limited in their ability to respond to increasing hardships, making them especially vulnerable.

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Impacts on Human Health

In the Southwest, more than 90% of the population live in cities, the highest percentage of any U.S. region. Pavement and buildings retain heat, creating urban heat islands that make cities warmer than surrounding areas and drive residents’ vulnerability to heat-related illnesses.[6] Heat stress is the leading cause of weather-related death in the Southwest, with a greater number of deaths expected as heat waves increase in number, length, and intensity.[1] Elderly populations and low income households that may not have access to air conditioning are especially at risk from heat stress. High temperatures also contribute to poor air quality, including the formation of ground-level ozone, which poses a risk to people with asthma and other respiratory illnesses.

Health problems are expected to be further aggravated by disruptions to urban electricity and water supplies. Greater energy use for cooling during heatwaves is likely to place additional strain on the electric grid and could result in brownouts or power outages.[1] Greater water demand in growing cities and reduced water availability could also affect access to drinking water.

For more information on climate change impacts on human health, please visit the Health page.

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Impacts on Forests and Ecosystems

Projected increases in drought, wildfire, invasive species, and pests, as well as changes in the geographic ranges of species, will likely threaten native forests and other ecosystems in the Southwest.[1][4] More severe drought and warming temperatures are threatening forests in the region and making them more vulnerable to other stresses, including pests. Warmer, drier conditions, combined with the accumulation of dead trees and other fuel have contributed to an increase in the size of wildfires in recent decades, resulting in extensive and costly damage. Fire is a natural occurrence in the Southwest, but excessive wildfire destroys homes, transforms ecosystems, threatens public health, and damages the economy. The 2003 Grand Prix fire in southern California alone caused $1.2 billion in damages.[1]

Multiple Climate Stressors and Piñon Pine Die-off

Photos taken from the same vantage point near Los Alamos, New Mexico, in 2002 (left) and in 2004 (right). Source: USGS (2004)

Climate change can intensify multiple stresses that push a species past a survival threshold. In 2000-2003, the combination of severe drought and unusually high temperatures led to a significant die-off of piñon pines in the Four Corners region of the Southwest.[7] Piñon pines are very drought tolerant and have survived dry periods in the past. However, in 2000-2003, high temperatures worsened drought conditions, making the piñons more susceptible to pine bark beetle attacks. In some areas, more than 90% of the piñons died, resulting in major ecosystem changes over a large area.[7] Warmer winter temperatures are also leading to worse bark beetle outbreaks because more beetles are able to survive through the winter and reproduce.[1]

Approximately 40% of the region is estimated to be vulnerable to changes in the distribution of abundant plant species as a result of recent and projected climate change.[1] Fires will likely change the location of forests and other ecosystems,[1] and changes in climate will likely drive the migration of species northward or to higher elevations as species colonize areas with more tolerable climatic conditions.[4] In California, over 3,000 native plant species are expected to face reductions in hospitable geographic range.[3] Iconic species and landscapes, such as that of the Saguaro cactus in the Sonoran Desert, are also being threatened.

For more information on climate change impacts on forests, please visit the Forests page.

To learn more about climate change impacts on ecosystems, please visit the Ecosystems page.

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Impacts on Agriculture

California produces more than half the nation’s high-value specialty crops, including many types of fruits, vegetables, and nuts.[1] Future production of these crops is likely to be affected by both reduced water availability and rising temperatures, resulting in local economic challenges and increasing food prices across the nation. The majority of the Southwest utilize irrigated croplands. As the region continues to become warmer and drier and as the population grows, more freshwater may be diverted from irrigation use to urban areas.[1] Warmer temperatures could also result in more heat waves, a longer frost-free season, and fewer cold snaps. These changes are likely to cause crops to ripen and mature early, reducing some crop yields.[1] As climate change intensifies, a northward shift in agricultural production in the region could occur.[1]

Livestock production in the Southwest is also expected to be affected by changes in water availability and temperatures. Pasture lands are not irrigated, potentially reducing grazing lands to drought while warming temperatures impose additional stresses on livestock.

For more information on climate change impacts on agriculture and food supply, please visit the Agriculture and Food Supply page.

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References

[1] USGCRP (2014). Garfin, G., G. Franco, H. Blanco, A. Comrie, P. Gonzalez, T. Piechota, R. Smyth, and R. Waskom, 2014: Ch. 20: Southwest. Climate Change Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program, 462-486.

[2] USGCRP (2014). Walsh, J., D. Wuebbles, K. Hayhoe, J. Kossin, K. Kunkel, G. Stephens, P. Thorne, R. Vose, M. Wehner, J. Willis, D. Anderson, S. Doney, R. Feely, P. Hennon, V. Kharin, T. Knutson, F. Landerer, T. Lenton, J. Kennedy, and R. Somerville, 2014: Ch. 2: Our Changing Climate. Climate Change Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program, 19-67.

[3] California Department of Water Resources, News Release, accessed 4/22/15.

[4] USGCRP (2009). Global Climate Change Impacts in the United States. Karl, T.R., J. M. Melillo, and T. C. Peterson (eds.). United States Global Change Research Program. Cambridge University Press, New York, NY, USA.

[5] USGCRP (2014). Bennett, T. M. B., N. G. Maynard, P. Cochran, R. Gough, K. Lynn, J. Maldonado, G. Voggesser, S. Wotkyns, and K. Cozzetto, 2014: Ch. 12: Indigenous Peoples, Lands, and Resources. Climate Change Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program, 297-317.

[6] USGCRP (2014). Luber, G., K. Knowlton, J. Balbus, H. Frumkin, M. Hayden, J. Hess, M. McGeehin, N. Sheats, L. Backer, C. B. Beard, K. L. Ebi, E. Maibach, R. S. Ostfeld, C. Wiedinmyer, E. Zielinski-Gutiérrez, and L. Ziska, 2014: Ch. 9: Human Health. Climate Change Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program, 220-256.

[7] NRC (2008). Ecological Impacts of Climate Change. Exit National Research Council. National Academies Press, Washington, DC, USA.

[8] US EPA (2015). Climate Change Indicators in the United States: A Closer Look: Temperature and Drought in the Southwest.

[9] USGCRP (2014). Georgakakos, A., P. Fleming, M. Dettinger, C. Peters-Lidard, Terese (T.C.) Richmond, K. Reckhow, K. White, and D. Yates, 2014: Ch. 3: Water Resources. Climate Change Impacts in the United States: The Third National Climate Assessment, J.M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program, 69-112.

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Climate Change Impacts

Climate Impacts in the Great Plains

On This Page:

Overview

Vulnerable Communities

Water Resources

Agriculture

Ecosystems

Overview

Key Points

Warmer winters are altering crop growth cycles and will require new agriculture and management practices as climate change impacts increase.

Projected increases in temperature and drought frequency will further stress the High Plains Aquifer, the primary water supply of the Great Plains.

Changes in water availability are likely to present challenges to agricultural irrigation and threaten key wetland habitats.

Older residents in rural areas and people living on Native American reservations are especially vulnerable to the impacts of climate change.

The Great Plains is home to the Rocky Mountains, prairie and grassland ecosystems, and the American Bison. Credit: USGCRP (2014)The Great Plains stretch from Canada to Mexico across the midsection of the country and consist of relatively flat plains that span from mountain elevations to sea level. The Plains are made up of a broad range of ecosystems, including forests, rangelands, marshes, and desert.[1] This coincides with a highly diverse climate and large geographic variation in temperature and precipitation across the region.

Because the Great Plains extend the entire north-south length of the United States, the region experiences a wide range of seasonal and average annual temperatures. In the mountains of Montana and Wyoming, average temperatures are less than 40°F, while in southern Texas, it is 70°F.[1] Warming temperatures are being felt across the Great Plains. North Dakota's average temperature has increased faster than any other state in the contiguous United States, and the number of days with temperatures over 100°F is projected to double in the Northern Plains by 2050.[1] The Southern Plains are projected to experience more extreme heat, with four times the number of days over 100°F than is currently experienced in the area. These temperature changes are expected to occur largely in the summer, but winter temperatures will also increase in the Northern Plains. Higher temperatures lead to greater evaporation and surface water losses, more heat stress, and increased energy demand for cooling.[1]

Related Links

EPA:

EPA, A Student's Guide to Global Climate Change: Effects on People and the Environment

EPA Region 6 (including the Great Plains states of NM, OK, and TX)

EPA Region 7 (including the Great Plains states of KS, ND, NE, and SD)

EPA Region 8 (including the Great Plains states of CO, MT, and WY)

EPA Climate Change Indicators: Length of Growing Season

EPA Climate Change Indicators: Ragweed Pollen Season

Other:

USGCRP Global Climate Change Impacts in the United States: Great Plains

USDA Regional Climate Hubs: Climate Risks in the Southern Plains(2 pp, 318 K, About PDF)

USDA Regional Climate Hubs: Climate Risks in the Northern Plains(2 pp, 945 K, About PDF)

NRC America's Climate Choices: Advancing the Science of Climate Change Exit

ITEP, Tribes & Climate Change Exit

The Great Plains has a distinct north-south gradient in average temperature patterns (left), with a hotter south and colder north. For precipitation (right), the regional gradient runs east-west, with a wetter east and a much drier west. Averages shown here are for the period 1981-2010. Source: USGCRP (2014)[1]

Click the image to view a larger version.The Great Plains has a distinct east-west gradient in average precipitation, with eastern Texas and Oklahoma experiencing more than 50 inches per year, while some of Montana, Wyoming, and western Texas receive less than 15 inches per year.[1] Climate change projections indicate that future precipitation patterns will vary across the region and at local scales. In northern states, the amount of winter and spring precipitation and the number of days with heavy downpours and snowfall are projected to increase.[1][2] In the central Great Plains, less summer rainfall is projected and could lead to drier summers in some areas. Southern states, including Texas and Oklahoma, are also projected to experience longer periods without rainfall.[1]

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Impacts on Vulnerable Communities

The Great Plains is home to a diverse cultural, geographical, and economic population that will experience the impacts of climate change in different ways. Climate change related impacts, including heat waves and extreme weather events, have disproportionate effects on vulnerable groups, including young, elderly, ill, and low income populations.[3] In the Great Plains, remotely located populations, including 70 recognized indigenous tribes and a growing proportion of elderly residents, face greater challenges in responding to climate change because of a lack of development, public health resources, and access to other public services and communication systems.[1] Language barriers for indigenous groups can also impact the ability to respond to climate extremes.

Climate change is also affecting tribal community traditions and culture.[1] Earlier onset of spring is changing the timing of rituals, and regions have faced the decline and disappearance of some culturally important plants and animals. For centuries, tribal groups have adapted to changes in the climate, but currently face heightened constraints of physical and political boundaries, poverty, and a lack of resources.[1][3] Despite these challenges, some groups are actively working to establish long-term sustainability plans that will foster adaptation and protection of important cultural resources.

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Impacts on Water Resources

Water-level changes in the High Plains Aquifer between the start of irrigation (around 1950) and 2011. Declines in water level have been observed across much of the southern portion of this aquifer. Source: USGS (2013)[4]

USGS has also provided a video of aquifer declines.

	Click the image to view a larger version.As patterns of temperature and precipitation change, the Great Plains region is expected to face increased competition for water supplies for use by homes, business, agriculture, and energy production.[1] Water in this region comes largely from the High Plains Aquifer system, made up largely of the Ogallala aquifer. The High Plains Aquifer system is one of the largest freshwater aquifers in the world and underlies approximately 111 million acres in parts of Colorado, Kansas, Nebraska, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming.[4] Nearly 30% of all irrigated lands in the United States reside above this aquifer, making it one of the primary agricultural regions in the nation.[4][5] The High Plains Aquifer also provides drinking water for more than 80% of the residents living over the aquifer and is key to the region's energy production.[1][5]

Long-term declines in the water level within the High Plains Aquifer have resulted from greater water discharge than recharge.[4] Discharge (or withdrawal) occurs largely by irrigation, which has resulted in an average water level decline of 14.2 feet since irrigation began around 1950. This translates to an 80 trillion gallon reduction in water storage within the aquifer.[4] Recharge (or replenishing) comes primarily from precipitation. In the northern portion of the Great Plains, rain can recharge the aquifer quickly.[1] However, with climate change, precipitation in the winter and spring is projected to increasingly fall in the form of very heavy precipitation events, which can increase flooding and runoff that reduce water quality and cause soil erosion.[1] In the southern portion of the region, little recharge occurs, so declines in the aquifer's water level are much greater (see figure of High Plains Aquifer).[4] Climate change will worsen this situation by causing drier conditions and increasing the need for irrigation.[1]

For more information on climate change impacts on water, please visit the Water Resources Impacts page.

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Impacts on Agriculture

Agriculture in the Great Plains utilizes more than 80% of the land area. In 2012, agriculture in the region was estimated to have a total market value of $92 million, made up largely of crop (43%) and livestock (46%) production.[1] Projected climate change will have many impacts on this sector. Some impacts may provide short-term benefits, but negative effects are also likely in this time frame. In the long-term, climate impacts will have increasingly detrimental effects that increase variability in crop and agricultural production.[1][6] Climate change may also cause a northward shift in lands used for agricultural production as temperature and water stresses rise, especially in the southern portion of the region.[1]

Crops

Center pivot sprinkler irrigation system located on a winter wheat cover crop in Morton, Texas. Credit: USDAIn the Northern Plains, crop yields benefit from increased precipitation in winter and spring. However, if the fields become too wet, planting may be delayed and affect yields.[1] The projected heavier rainfall will also increase erosion and nutrient runoff, which could have detrimental impacts on crops and agricultural soil quality. Warmer temperatures lengthen the growing season, which could increase plant growth or allow for a second planting. Higher levels of carbon dioxide may also increase plant growth. However, summer precipitation is not projected to rise, which increases vulnerability to drought conditions, while higher summer temperatures are likely to reduce plant productivity. In the Central and Southern Plains, the higher temperatures and decreased precipitation will increase irrigation demands. If irrigation is reduced to conserve water and farmers transition to dryland agriculture, crop yields could be reduced by a factor of two.[1]

The Great Plains is already experiencing warmer winters, and further temperature increases are projected for this season. These conditions can increase the survival of some pests and invasive weeds.[1] Additionally, the dormancy period for winter crops is shortening, increasing the potential for damage by spring freezes and reducing yields of some important livestock feed crops, such as winter wheat. As climate impacts worsen in the future, agricultural practices will face increased risks that require new considerations and management strategies.[1][6]

Livestock

Daily water withdrawals associated with livestock operations in 2010. Source: USGS (2014)[10]

Click the image to view a larger version.Livestock production is a major component of the economy in the Great Plains. By value, Texas produces the most cattle in the United States.[7] Warmer temperatures and extreme heat stress animals and cause declines in meat, milk, and egg production.[6] Diseases may also increase as temperature and moisture conditions become more favorable for disease spread and range expansion. Additional expenses may also be incurred as the need to cool animal buildings increases.[6]

Drought and increasing demand for available fresh water is already affecting the livestock industry. Animal operations require large quantities of water for drinking water, feedlot operations, dairy farms, and other on-farm needs. Some of the largest water withdrawals in the country occur in the Great Plains, with Texas having the highest water usage for livestock in the country.[8] Continued livestock production and associated water usage in this region will exacerbate water shortages as climate change impacts continue.

For more information on climate change impacts on agriculture, please visit the Agriculture and Food Supply page.

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Impacts on Ecosystems

The ragweed pollen season has increased across most of the Great Plains and Midwest. This figure shows the change in the length of the ragweed pollen season between 1995 and 2013 at 11 locations. Red circles indicate a longer pollen season and the blue circle represents a shorter season. Larger circles indicate larger changes. Source: US EPA (2015)[11]

Click the image to view a larger version.Climate and land use are changing simultaneously in the Great Plains and altering many ecosystems.[1] Land development for energy production and urban sprawl are increasing habitat fragmentation. This lessens the ability of plants and animals to adapt by moving to new areas in response to warmer temperatures or changes in water availability. Climate change is also increasing pest outbreaks, spreading invasive species, accelerating wildfire activity, and changing plant flowering times. An increase in frost-free days in the Great Plains have lengthened the pollen season for the common allergen ragweed, increasing the likelihood of allergic reactions and associated health impacts.[1]

Image of the wetland ecosystem known as prairie potholes. Credit: USGSClimate change is affecting critical game species in the Great Plains, including a number of birds (including ducks, geese, and quail), mammals (including moose and deer), and fish (including bass).[9] Many of these animals rely on the availability of shallow lakes that periodically dry out. These areas, known as Prairie Potholes (in the north) or playa lakes (in the south), provide habitat for many species to mate and nurture offspring. The lakes also help recharge the High Plains Aquifer.[9] Agricultural practices have changed more than 70% of the large seasonal lakes in the southern Great Plains. As temperatures continue to rise, the bird and fish populations that rely on these areas are increasingly impacted.[1]

For more information on climate change impacts on ecosystems, please visit the Ecosystems Impacts page.

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References

[1] USGCRP (2014). Shafer, M., D. Ojima, J.M. Antle, D. Kluck, R.A. McPherson, S. Petersen, B. Scanlon, and K. Sherman, 2014: Ch 19: Great Plains. Climate Change Impacts in the United States: The Third National Climate Assessment, J.M. Melillo, Terese (T.C.) Richmond, and G.W. Yohe, Eds., U.S. Global Change Research Program, 441-461.

[2] USGCRP (2014).  Walsh, J., D. Wuebbles, K. Hayhoe, J. Kossin, K. Kunkel, G. Stephens, P. Thorne, R. Vose, M. Wehner, J. Willis, D. Anderson, S. Doney, R. Feely, P. Hennon, V. Kharin, T. Knutson, F. Landerer, T. Lenton, J. Kennedy, and R. Somerville, 2014: Ch. 2: Our Changing Climate. Climate Change Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program, 19-67.

[3] USGCRP (2014).  Bennett, T. M. B., N. G. Maynard, P. Cochran, R. Gough, K. Lynn, J. Maldonado, G. Voggesser, S. Wotkyns, and K. Cozzetto, 2014: Ch. 12: Indigenous Peoples, Lands, and Resources. Climate Change Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program, 297-317.

[4] USGS (2013). McGuire, V.L., 2013. Water-level and storage changes in the High Plains aquifer, predevelopment to 2011 and 2009-11: U.S. Geological Survey Scientific Investigations Report 2012-5291, 15 p.

[5] United States Department of Agriculture (2012). Ogallala Aquifer Initiative 2011 Report.(7 pp, 436 K, About PDF)

[6] USGCRP (2014). Hatfield, J., G. Takle, R. Grotjahn, P. Holden, R. C. Izaurralde, T. Mader, E. Marshall, and D. Liverman, 2014: Ch. 6: Agriculture. Climate Change Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program, 150-174.

[7] United States Department of Agriculture (2014). Economic Research Service. Market Value of livestock, poultry, and their products sold in 2012.

[8] USGS (2014). Maupin, M.A., Kenny, J.F., Hutson, S.S., Lovelace, J.K., Barber, N.L., and Linsey, K.S., 2014. Estimated use of water in the United States in 2010: U.S. Geological Survey Circular 1405, 56 p.

[9] USGCRP (2009). Global Climate Change Impacts in the United States. Karl, T. R., J. M. Melillo, and T. C. Peterson (eds.). United States Global Change Research Program. Cambridge University Press, New York, NY, USA.

[10] USGS (2014). Livestock Water Use.

[11] US EPA (2015). Climate Change Indicators in the United States: Ragweed Pollen Season.

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Select a state below to learn about climate change health impacts, related public health concerns, and how you can take action to prepare for or respond to climate change. Key resources for each state are also provided. Information about impacts is based on The Impacts of Climate Change on Human Health in the United States: A Scientific Assessment and the National Climate Assessment.

Find additional resources on the Climate Change and Human Health Risks in Your State page. Learn more about other climate change impacts in your state.

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On This Page:

Overview

Temperature, Energy Demand, and Energy Supply

Water Availability and Energy

Sea Level Rise, Storm Surge, and Extreme Events

Wind Speed, Cloud Cover, and Renewable Energy

Overview

Key Points

Climate change is likely to both increase electricity demand for cooling in the summer and decrease electricity, natural gas, heating oil, and wood demand for heating in the winter. New infrastructure investments may be necessary to meet increased energy demand, especially peak demand during heat waves.

Climate change could affect the amount of water available to produce electricity or extract fuel. In areas where water is already scarce, competition for water between energy production and other uses could increase.

Sea level rise and more frequent intense storms could disrupt energy production and delivery by damaging electricity infrastructure, fuel delivery infrastructure and equipment, power plants, or storage facilities.

Changes in temperature, precipitation, sea level, and the frequency and severity of extreme events will affect how much energy is produced, delivered, and consumed in the United States.

Energy plays an important role in many aspects of our lives. For example, we use electricity for lighting and cooling. We use fuel for transportation, heating, and cooking. Our energy production and use is interconnected with many other aspects of modern life, such as water consumption, use of goods and services, transportation, economic growth, land use, and population growth. Our production and use of energy (most of which comes from fossil fuels) also contributes to climate change, accounting for more than 84% of U.S. greenhouse gas emissions.[1]

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Temperature, Energy Demand, and Energy Supply

Increases in temperature will likely increase our energy demand, as well as change our ability to produce electricity and deliver it reliably.

In a warmer climate, Americans will use more electricity for air conditioning and less natural gas, oil, and wood for heating. If the nation's climate warms by 1.8Â°F, the demand for energy used for cooling is expected to increase by about 5-20%, while the demand for energy used for heating is expected to decrease by about 3-15%.[2] Net expenditure in annual heating and cooling could increase by 10% ($26 billion in 1990 dollars) with a 4.5Â°F warming by the end of the century, and by 22% ($57 billion in 1990 dollars) with a warming of 9.0Â°F.[3] Heating demand would decrease the most in the northern United States, and cooling demand would increase the most in the southern United States. Since demand for electricity for cooling is expected to increase as a result of temperature increase and extreme heat events, the balance in energy delivery is likely to shift from natural gas and fuel oil used for heating to electricity used for air conditioning.[3] Changes in energy demand will likely affect greenhouse gas emissions, but the net effect depends on which energy sources, including alternative energy, are used for electricity and heating.

Related Links

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		Warming is likely to increase summer peak electricity demand in most regions of the United States.[3] Meeting increases in this peak demand could require investments in new energy generation and distribution infrastructure, and new mechanisms will need to manage system reliability and peak demand, which can be more expensive than average demand levels.[3] For example, based on a 6.3 to 9Â°F temperature increase, climate change could increase the need for additional electric generating capacity by roughly 10-20% by 2050. This would require hundreds of billions of dollars in additional investment.[2]

A warmer climate may reduce the efficiency of power production for many existing fossil fuel and nuclear power plants because these plants use water for cooling. The colder the water, the more efficient the generator. Thus, higher air and water temperatures could reduce the efficiency with which these plants convert fuel into electricity.[3]

Energy demand is expected to shift by the end of the century. The number of cooling (or heating) "degree days" refers to the sum of the number of degrees that each day's average temperature is hotter (or colder) than 65°F over the course of a year.  As the figure shows, the increase in the number of cooling degree days is expected to be larger than the decrease in number of heating degree days, comparing the historic average and the projected average over the final two decades of this century. Source: USGCRP (2009)

Click the image to view a larger version.

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Water Availability and Energy

Water and energy flows. Source: U.S. DOE (PDF)

Click the image to view a larger version.Energy and water systems are connected. Energy is needed to pump, transport, and treat drinking water and wastewater. Cooling water is needed to run many of today's power plants. Hydroelectricity (electricity produced by running water) is itself an important source of power in parts of the United States.

Changes in precipitation, increased risk of drought, reduced snowpack, and changes in the timing of snowmelt in spring will influence our patterns of energy and water use. For example:

Power plants can require large amounts of water for cooling. On average, a kilowatt-hour of electricity (enough power to run 400 typical compact-fluorescent light bulbs for an hour) requires 25 gallons of water to be withdrawn from rivers or lakes.[2] Parts of the Southeast and Southwest face increased competition for water to meet the demands of population and economic growth while also protecting natural ecosystems. Many local governments in these regions have slowed or stopped plans for new power plants that require large withdrawals of water due to concerns about adequate availability of cooling water.[6]

More frequent and severe heat waves will likely increase the demand for electricity in the Southeast and Southwest. At the same time, these areas are likely to experience reduced water supplies due to increased temperature and evaporation, as well as possible decreased rainfall. Since water is necessary for electricity production, these combined effects could stress water resources. For more information about climate change impacts in the Southeast and Southwest, please visit the Southeast ImpactsÂ and Southwest ImpactsÂ pages.

Hydroelectric power plants are sensitive to the volume and timing of stream flows. In some regions, especially during times of increased rainfall, dam operators may have to allow some water to bypass the electric turbines to prevent downstream flooding.[2] Maintaining stream flow for hydroelectric dams could present conflicts with other activities, such as salmon habitat restoration in the Pacific Northwest.[4]

Growing crops for biomass and biofuel energy could stress water resources in certain regions, depending on the type of crop, where it is grown, agricultural production in the region, and current water and nutrient management practices.[5] Given the many factors involved, more research is needed to understand how climate change may affect these resources.[3]

Rising temperatures, increased evaporation, and drought may increase the need for energy-intensive methods of providing drinking and irrigation water. For example, desalinization plants can convert salt water into freshwater, but consume a lot of energy. Climate change may also require irrigation water to be pumped over longer distances, particularly in dry regions across the western United States.[3]

For more information about the impacts of climate change on water resources, please visit the Water Impacts page.

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Sea Level Rise, Storm Surge, and Extreme Events

Before and after photographs of the "Mars" offshore drilling and production platform, damaged by Hurricane Katrina in the Gulf of Mexico. Source: CCSP (2008)A large portion of U.S. energy infrastructure is located in coastal areas and therefore sensitive to sea level rise and storm surge. For example, fuel ports and the generation and transmission lines that bring electricity to major urban coastal centers are at risk. Changes in the frequency and severity of storms and other extreme events may also damage energy infrastructure, resulting in energy shortages that harm the economy and disrupt peoplesâ€™ daily lives.Â

A substantial portion of U.S. energy facilities are located on the Gulf Coast or offshore in the Gulf of Mexico. Several coastal power plants in the United States are less than three feet above sea level, and facilities that import or export coal, gas, and oil are also located in coastal regions.[3] Sea level rise and more intense storms and hurricanes in coastal areas could increase the risk of energy supply disruptions.

Power plants susceptible to sea level rise in California by type and size. Source: USGCRP (2014)

Click the image to view a larger version.Several thousand oil drilling platforms offshore of the Gulf Coast are vulnerable to extreme weather events. For example, Hurricanes Katrina and Rita damaged more than 100 platforms and damaged 558 pipelines in 2005, impacting markets as far away as New York and New England.[6]

Flooding and intense storms can damage power lines and electricity distribution equipment. These events may also delay repair and maintenance work. Electricity outages can have serious impacts on other energy systems as well. For example, oil and gas pipeline disruptions following extreme weather events are often caused by power outages rather than physical damage to the infrastructure.[2]

Railways and marine transportation that move large amounts of oil and coal in the United States are also vulnerable to climate change. More intense rainfall and storms can threaten railways by washing out railway beds. Changes in precipitation could affect marine transportation by reducing the navigability of rivers.Â

For more information about the impacts of climate change on coastal areas, please visit the Coastal Impacts page.

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Renewable Biofuels

The Energy Policy Act of 2005 established the first Renewable Fuel Standard (RFS), mandating that biofuels be integrated into transportation fuel to reduce greenhouse gas emissions.

The Energy Independence Security Act (EISA) of 2007 increased the required amount of renewable fuel to 36 billion gallons per year by 2022.

Annually, the EPA sets volume requirements for each category of renewable fuel. The volumes are determined by technology and the availability of each type of renewable fuel.

Every three years, the EPA is required to send a report to Congress that evaluates the environmental and resource conservation impacts of increased biofuel production and use.

For more information about the RFS, visit EPA's RFS page. For specific information about the environmental assessment, read the First Triennial Report to Congress.

Wind Speed, Cloud Cover, and Renewable Energy

The impacts of climate change on wind and solar power is still a developing area of research due to the challenges involved in modeling wind and cloud cover changes at the necessary spatial scales.Â Â

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References

[1]Â EPA (2015). Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2013. U.S. Environmental Protection Agency (EPA).

[2]Â CCSP (2008). Effects of Climate Change on Energy Production and Use in the United States. A Report by the U.S. Climate Change Science Program and the subcommittee on Global change Research. Wilbanks, T.J., V. Bhatt, D.E. Bilello, S.R. Bull, J.Ekmann, W.C. Horak, Y.J. Huang, M.D. Levine, M.J. Sale, D.K. Schmalzer, and M.J. Scott. Department of Energy, Office of Biological & Environmental Research, Washington, DC, USA.

[3]Â USGCRP (2014). Dell, J., S. Tierney, G. Franco, R. G. Newell, R. Richels, J. Weyant, and T. J. Wilbanks, 2014: Ch. 4: Energy Supply and Use. Climate Change Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program, 113-129. doi:10.7930/J0BG2KWD.

[4]Â IPCC (2014). Climate Change 2014: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel. Field, C.B., V.R. Barros, D.J. Dokken, K.J. Mach, M.D. Mastrandrea, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L.White (eds.) Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

[5]Â NRC (2008). Water Implications of Biofuels Production in the United States. Committee on Water Implications of Biofuels Production in the United States, National Research Council. The National Academies Press, Washington, D.C.

[6]Â USGCRP (2009). Global Climate Change Impacts in the United States. â€œClimate Change Impacts by Sectors: Energy Supply and Use.â€? Karl, T.R., J.M. Melillo, and T.C. Peterson (eds.). United States Global Change Research Program. Cambridge University Press, New York, NY, USA.

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Climate Impacts on Coastal Areas

On This Page:

Overview

Sea Level Rise

Changes in Storm Surge and Precipitation

Coastal Water Temperature

Coral Reefs and Shellfish

Overview

Key Points

Climate change threatens coastal areas, which are already stressed by human activity, pollution, invasive species, and storms.

Sea level rise could erode and inundate coastal ecosystems and eliminate wetlands.

Warmer and more acidic oceans are likely to disrupt coastal and marine ecosystems.

Coastal development reduces the ability of natural systems to respond to climate changes.

The coastline of the United States is highly populated.  Approximately 25 million people live in an area vulnerable to coastal flooding.[1][2] Coastal and ocean activities, such as marine transportation of goods, offshore energy drilling, resource extraction, fish cultivation, recreation, and tourism are integral to the nation's economy, generating 58% of the national gross domestic product (GDP).[2] Coastal areas are also home to species and habitats that provide many benefits to society and natural ecosystems.

The National Oceanic and Atmospheric Administration (NOAA) projects that sea level rise will increase flooding in Charleston, South Carolina. Source: NOAA Coastal Services Center (2012)

Click the image to see a larger version.Climate change can affect coastal areas in a variety of ways. Coasts are sensitive to sea level rise, changes in the frequency and intensity of storms, increases in precipitation, and warmer ocean temperatures. In addition, rising atmospheric concentrations of carbon dioxide (CO2) are causing the oceans to absorb more of the gas and become more acidic. This rising acidity can have significant impacts on coastal and marine ecosystems.

The impacts of climate change are likely to worsen problems that coastal areas already face. Confronting existing challenges that affect man-made infrastructure and coastal ecosystems, such as shoreline erosion, coastal flooding, and water pollution, is already a concern in many areas. Addressing the additional stress of climate change may require new approaches to managing land, water, waste, and ecosystems.

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Climate Ready Estuaries

Climate Change Indicators: Sea Level

Climate Change Indicators: Ocean Acidity

A Reef Manager's Guide to Coral Bleaching

Coral Reef Management in American Samoa

Other:

USGCRP: Global Climate Change Impacts on US Coasts

NOAA: Sea Level Rise Viewer

NOAA: Sea Levels Trends

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NAS: Adapting to the Impacts of Climate Change Exit

USGS: Sea Level Rise

USGCRP: Coastal Sensitivity to Sea-Level Rise - A Focus on the Mid-Atlantic Region

USGCRP: Adaptation for Climate-Sensitive Ecosystems and Resources

Sea Level Rise

Observed changes in sea level relative to land elevation in the United States between 1960 and 2014. Source: EPA (2015)

Click the image to view a larger version.

Since 1901, global sea level has risen approximately eight inches.[3][4]

In a particular location, the change in sea level that is observed will be affected by the increase in global sea level as well as land movement up or down. The motion of land can be caused by subsiding coastal lands, oil and water extraction activities, melting ice, or tectonic movement. The terms "local" or "relative" sea level refer to both the global change in sea level and the effects of land motion.

Where the land is sinking, the rate of relative sea level rise is larger than the global rate. Some of the fastest rates of relative sea level rise in the United States are occurring in areas where the land is sinking, including parts of the Gulf Coast. For example, coastal Louisiana has seen its relative sea level rise by eight inches or more in the last 50 years,[2] which is about twice the global rate. Subsiding land in the Chesapeake Bay area worsens the effects of relative sea level rise, increasing the risk of flooding in cities, inhabited islands, and tidal wetlands.[2]

Sea Level Rise and Coastal Flooding Impacts Viewer

The National Oceanic and Atmospheric Administration has developed a tool to visualize the potential impacts of sea level rise on coastal communities in the United States.

<img alt="Screenshot of the NOAA sea level rise and coastal flooding impacts tool. The sample map shows a region around Tampa, Florida and a toolbar on the left indicates varying water depths, low-lying areas and other functions of the tool." title="Screenshot of the NOAA sea level rise and coastal flooding impacts tool. The sample map shows a region around Tampa, Florida and a toolbar on the left indicates varying water depths, low-lying areas and other functions of the tool." height="534" width="928" class="center media-element file-full" typeof="foaf:Image" src="/sites/production/files/styles/large/public/2016-05/noaaslrtool.jpg" />NOAA's sea level rise and coastal flooding impacts viewer. Source: NOAA (2012)

Mostly because of these differences in land motion, estimates of future relative sea level rise vary for different regions. Climate change models project that global sea level rise will accelerate in the 21st century. Models based on thermal expansion and ice melt estimate that global sea level is very likely to rise between 1 and 3 feet by the end of the century. Typically, these models do not, however, incorporate all of the possible responses of ice sheets to warmer temperatures, which could further raise sea level, but is unlikely to add more than one foot.[2][4][5]

For more information on recent and future sea level rise, please visit the Science section.

Growing populations and development along the coasts increase the vulnerability of coastal ecosystems to sea level rise. Development can block the inland migration of wetlands in response of sea level rise, and change the amount of sediment delivered to coastal areas and accelerate erosion. For example, coastal Louisiana lost approximately 2000 square miles of wetlands in recent decades due to human alterations of the Mississippi River's sediment system and oil and water extraction that has caused land to sink. As a result of these changes, wetlands do not receive enough sediment to keep up with rising seas, and may no longer function as natural buffers to flooding.[6]

Rising sea level also increases the salinity of ground water and pushes salt water further upstream. Higher salinity can make water undrinkable without desalination, and harms many aquatic plants and animals.[2]

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Impacts of Changes in Storm Surge and Precipitation

Coastal areas are also vulnerable to increases in the intensity of storm surge and heavy precipitation. Storm surges flood low-lying areas, damage property, disrupt transportation systems, destroy habitat, and threaten human health and safety. For example, low-lying areas of New York City, Long Island, and New Jersey were flooded by several feet of water by the storm surge from Superstorm Sandy in 2012.[2][5] Sea level rise could magnify the impacts of storms by raising the base on which storm surges build.[7]

Climate change is likely to bring heavier rainfall to some coastal areas, which would also increase runoff and flooding. In addition, warmer temperatures in mountain areas could lead to more spring runoff due to melting of snow. In turn, increases in spring runoff may also threaten the health and quality of coastal waters. Some coastal areas, such as the Gulf of Mexico and Chesapeake Bay, are already experiencing "dead zones." Dead zones occur when land-based sources of pollution (e.g., agricultural fertilizers) contribute to algal blooms. When the algae sink and decompose, the process depletes the oxygen in the water.  As increases in spring runoff bring more nitrogen, phosphorus, and other pollutants into coastal waters, many aquatic species could be threatened.[1]

Decreases in precipitation could also increase the salinity of coastal waters. Droughts reduce fresh water input into tidal rivers and bays, which raises salinity in estuaries, and enables salt water to mix further upstream.[2]

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Impacts of Coastal Water Temperature

Coastal waters have warmed during the last century, and are very likely to continue to warm in the 21st century [2][5], potentially by as much as 4 to 8°F.[8] This warming may lead to big changes in coastal ecosystems, affecting species that inhabit these areas.

Warming coastal waters cause suitable habitats of temperature-sensitive species to shift poleward. Some areas have recently seen range shifts in both warm- and cold-water fish and other marine species. Pollock, halibut, rock sole, and snow crab in Alaska and mangrove trees in Florida are a few of the species whose habitats have already begun to shift.[2][5] Suitable habitats of other species may also shift, because they cannot compete for limited resources with the southern species that are moving northward.[1]

For more information on climate change impacts on species, visit the Ecosystems page.

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Climate Ready Estuaries Program

Estuaries are particularly sensitive to many projected impacts of climate change, including erosion from rising seas, changes in storms frequency and intensity, and the amount of precipitation. EPA's Climate Ready Estuaries program works with National Estuary Programs and other coastal managers to:

Assess climate change vulnerabilities.

Engage and educate stakeholders.

Develop and implement adaptation strategies.

Share lessons learned with other coastal managers.

The Climate Ready Estuaries website provides resources for estuaries and coastal programs that are interested in learning more about climate change impacts and adaptation.

To learn more about estuaries, visit the National Estuaries Program web page.

Impacts to Coral Reefs and Shellfish

Bleached brain coral. Source: NOAAHigher sea surface temperatures increase the risks of coral bleaching, which can lead to coral death and the loss of critical habitat for other species.[2] The rising concentration of carbon dioxide (CO2) in the atmosphere has increased the absorption of CO2 in the ocean, which subsequently makes the oceans more acidic. This trend is very likely to continue in the coming decades. A more acidic ocean adversely affects the health of many marine species, including plankton, mollusks, and other shellfish. In particular, corals can be very sensitive to rising acidity, as it is difficult for them to create and maintain the skeletal structures needed for their support and protection. Corals in the Florida Keys, Hawaii, Puerto Rico, and other U.S. territories are likely to experience substantial losses if CO2 concentrations in the atmosphere continue to rise at their current rate.[2]

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References

[1] FEMA (2008). Coastal AE Zone and VE Zone Demographics Study and Primary Frontal Dune Study to Support the NFIP. Washington, DC: Federal Emergency Management Agency Technical Report, 98p.

[2] USGCRP (2014). Moser, S. C., M. A. Davidson, P. Kirshen, P. Mulvaney, J. F. Murley, J. E. Neumann, L. Petes, and D. Reed, 2014: Ch. 25: Coastal Zone Development and Ecosystems. Climate Change Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program, , 579-618.

[3] USGCRP (2014). Walsh, J., D. Wuebbles, K. Hayhoe, J. Kossin, K. Kunkel, G. Stephens, P. Thorne, R. Vose, M. Wehner, J. Willis, D. Anderson, S. Doney, R. Feely, P. Hennon, V. Kharin, T. Knutson, F. Landerer, T. Lenton, J. Kennedy, and R. Somerville. Ch. 2: Our Changing Climate. Climate Change Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program, 19-67.

[4] IPCC (2013). Rhein, M., S.R. Rintoul, S. Aoki, E. Campos, D. Chambers, R.A. Feely, S. Gulev, G.C. Johnson, S.A. Josey, A. Kostianoy,  C. Mauritzen, D. Roemmich, L.D. Talley and F. Wang. Observations: Ocean. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

[5] IPCC (2014). Wong, P.P., I.J. Losada, J. Gattuso, J. Hinkel, A. Khattabi, K. McInnes, Y. Saito, and A Sallenger. Coastal systems and low-lying areas. In: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Field, C.B., V.R. Barros, D.J. Dokken, K.J. Mach, M.D. Mastrandrea, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L.White (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

[6] CCSP (2008). Impacts of Climate Change and Variability on Transportation Systems and Infrastructure: Gulf Coast Study, Phase I. A Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. Savonis, M. J., V.R. Burkett, and J.R. Potter (eds.). Department of Transportation, Washington, DC, USA, 445 pp.

[7] NRC (2010). Adapting to the Impacts of Climate Change. National Research Council. The National Academies Press, Washington, DC, USA.

[8] USGCRP (2009). Global Climate Change Impacts in the United States, Coasts. Karl, T.R., J.M. Melillo, and T.C. Peterson (eds.). United States Global Change Research Program. Cambridge University Press, New York, NY, USA.

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Climate Change Impacts

Climate Impacts on Forests

On This Page

Overview

Forest Growth and Productivity

Disturbances

		Â

Key Points

Climate change will likely alter the frequency and intensity of forest disturbances, including wildfires, storms, insect outbreaks, and the occurrence of invasive species.

The productivity and distribution of forests could be affected by changes in temperature, precipitation and the amount of carbon dioxide in the air.

Climate change will likely worsen the problems already faced by forests from land development and air pollution.

Overview

In the United States, forests occupy approximately 740 million acres, about one third of the country's total land area.[2] America's forests provide many benefits and services to society, including clean water and air, recreation, wildlife habitat, carbon storage, climate regulation, and a variety of forest products.[2] Climate influences the structure and function of forest ecosystems and plays an essential role in forest health. A changing climate may worsen many of the threats to forests, such as pest outbreaks, fires, human development, and drought.

Extent and type of forest cover in the United States. View larger: U.S. Forest Service, National Atlas.Climate changes directly and indirectly affect theÂ growth and productivity of forestsÂ through changes in temperature, rainfall, weather, and other factors. In addition, elevated levels of carbon dioxide have an effect on plant growth. These changes influence complex forest ecosystems in many ways.

In conjunction with the projected impacts of climate change, forests face impacts from land development, suppression of natural periodic forest fires, and air pollution. Although it is difficult to separate the effects of these different factors, the combined impact is already leading to changes in our forests. As these changes are likely to continue in the decades ahead, some of the valuable goods and services provided by forests may be compromised. To learn more about examples of projected regional changes in forests, see the Northeast, Southeast, Southwest, and Alaska regional impacts pages.

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Related Links

EPA

Carbon Sequestration in Agriculture and Forestry

Climate Ready Estuaries

		Other

National Climate Assessment: Forests

USFS: Climate Change Resource Center

USDA: Climate Change

DOI: Climate Change

USGCRP: Climate Change and Agriculture, Land Resources, Water Resources, and Biodiversity

IPCC: Fifth Assessment ReportÂ Exit

Impacts on Forest Growth and Productivity

Many aspects related to climate change are likely to affect forest growth and productivity. Three examples are described below: increases in temperature, changes in precipitation, and increases in carbon dioxide (CO2).

Warming temperatures generally increase the length of the growing season. It also shifts the geographic ranges of some tree species. Habitats of some types of trees are likely to move north or to higher altitudes. Other species will be at risk locally or regionally if conditions in their current geographic ranges are no longer suitable.[2] For example, species that currently exist only on mountaintops in some regions may die out as the climate warms since they cannot shift to a higher altitude.

Climate change will likely increase the risk of drought in some areas and the risk of extreme precipitation and flooding in others. Increased temperatures alter the timing of snowmelt, affecting the seasonal availability of water. Although many trees are resilient to some degree of drought, increases in temperature could make future droughts more damaging than those experienced in the past. In addition, drought increases wildfire risk, since dry trees and shrubs provide fuel to fires. Drought also reduces trees' ability to produce sap, which protects them from destructive insects such as pine beetles.[5]

Carbon dioxide is required for photosynthesis, the process by which green plants use sunlight to grow. Given sufficient water and nutrients, increases in atmospheric CO2 may enable trees to be more productive, which may change the distribution of tree species. Growth will be highest in nutrient-rich soils with no water limitation, and will decrease with decreasing fertility and water supply.[2]

Projected shifts in forest types. The maps show recent and projected forest types. Major changes are projected for many regions. For example, in the Northeast, under a lower emissions scenario, the currently dominant maple-beech-birch forest type (red shading) is projected to be displaced by the oak-hickory forest type in a warmer future. Source: USGCRP (2009)

Click the image to view a larger version.

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Impacts of Disturbances

Climate change could alter the frequency and intensity of forest disturbances such as insect outbreaks, invasive species, wildfires, and storms. These disturbances can reduce forest productivity and change the distribution of tree species. In some cases, forests can recover from a disturbance. In other cases, existing species may shift their range or die out. In these cases, the new species of vegetation that colonize the area create a new type of forest.

The brown and red trees in this picture have been infested by mountain pine beetles near Winter Park, Colorado in May 2007. Source: CCSP (2008)Insect outbreaks often defoliate, weaken, and kill trees. For example, by 2007, pine beetles had damaged more than Â 650,000 acres of forest in Colorado and spruce beetles had damaged more than 3.7 million acres in southern Alaska and western Canada.[2] The hemlock woolly adelgid, an invasive species that is sensitive to cold weather and destroys Eastern hemlock, will likely extend its habitat north as the climate warms.[6] A lack of natural controls, such as predators or pathogens, as well as inadequate defenses in trees, can allow insects to spread. Climate change could contribute to an increase in the severity of future insect outbreaks. Rising temperatures may enable some insect species to develop faster, alter their seasonal life cycles, and expand their ranges northward. Invasive plant species can displace important native vegetation because the invasive species often lack natural predators. Climate change could benefit invasive plants that are more tolerant the environmental conditions resulting from climate change than are native plants.[2][5]

In 2011, wildfires consumed more than 8 million acres of forest in the U.S. (an area roughly the size of Maryland), causing 15 deaths and more than $1.9 billion in damages. Warm temperatures and drought conditions during the early summer contributed to this event.[3] Climate change is projected to increase the extent, intensity, and frequency of wildfires in certain areas of the country. Warmer spring and summer temperatures, coupled with decreases in water availability, dry out woody materials in forests and increase the risk of wildfire. Fires can also contribute to climate change, since they can cause rapid, large releases of carbon dioxide to the atmosphere.[2]

This figure shows annual wildfire-burned area (in millions of acres) from 1983 to 2015.  (The two lines represent two different reporting systems, shown for comparison).  The extent of area burned by wildfires each year appears to have increased since the 1980s. According to National Interagency Fire Center data, of the 10 years with the largest acreage burned, nine have occurred since 2000, including the peak year in 2015. This period coincides with many of the warmest years on record nationwide.  Source: Climate Change Indicators in the United States

Click the image to view a larger version.

Hurricanes, ice storms, and wind storms can cause damage to forests. Hurricanes Rita and Katrina in 2005 damaged a total of 5,500 acres of forest. The amount of carbon released by these trees as they decay is roughly equivalent to the net amount of carbon sequestered by all U.S. forests in a single year.[2]

Case Study: Effects of Climate Change on Rocky Mountain National Park Forests

Changes in Rocky Mountain National Park in Colorado demonstrate the impacts that many forests are experiencing or may experience in the future.

Summer temperatures have been increasing in the park, recent beetle outbreaks have been especially severe, snowpack has been melting earlier, and aÂ nearby glacier has shrunk.

Park managers anticipate additional warming, reductions in snowpack, shifts in habitats to higher elevations, and losses of some sensitive species.

The National Park Service is exploring ways to manage fire risks and minimize the impacts from invasive species.[4]

Disturbances can interact with one another, or with changes in temperature and precipitation, to increase risks to forests. For example, drought can weaken trees and make a forest more susceptible to wildfire or insect outbreaks. Similarly, wildfire can make a forest more vulnerable to pests.[2][3] The combination of drought and outbreaks of beetles has damaged piÃ±on pine forests in the Southwest.

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References

1. U.S. Forest Service (undated). USDA Forest Service: An Overview.Â

2. CCSP (2008). The Effects of Climate Change on Agriculture, Land Resources, Water Resources, and Biodiversity in the United States. Chapter 3: Land Resources: Forest and Arid Lands. A Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. Backlund, P. , A. Janetos, D. Schimel, J. Hatfield, K. Boote, P. Fay, L. Hahn, C. Izaurralde, B.A. Kimball, T. Mader, J. Morgan, D. Ort, W. Polley, A. Thomson, D. Wolfe, M. Ryan, S. Archer, R. Birdsey, C. Dahm, L. Heath, J. Hicke, D. Hollinger, T. Huxman, G. Okin, R. Oren, J. Randerson, W. Schlesinger, D. Lettenmaier, D. Major, L. Poff, S. Running, L. Hansen, D. Inouye, B.P. Kelly, L Meyerson, B. Peterson, and R. Shaw. U.S. Environmental Protection Agency, Washington, DC, USA.

3. USGCRP (2014). Groffman, P. M., P. Kareiva, S. Carter, N. B. Grimm, J. Lawler, M. Mack, V. Matzek, and H. Tallis, 2014: Ch. 8: Ecosystems, Biodiversity, and Ecosystem Services. Climate Change Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program, 195-219. doi:10.7930/J0TD9V7H.

4. NPS (2008). Climate Change in Rocky Mountain National Park: Preservation in the Face of Uncertainty. National Park Service, U.S. Department of the Interior.

5. USGCRP (2009). Global Climate Change Impacts in the United States. â€œClimate Change Impacts by Sectors: Ecosystems.â€? Karl, T.R., J.M. Melillo, and T.C. Peterson (eds.). United States Global Change Research Program. Cambridge University Press, New York, NY, USA.

6. USGCRP (2014). Horton, R., G. Yohe, W. Easterling, R. Kates, M. Ruth, E. Sussman, A. Whelchel, D. Wolfe, and F. Lipschultz, 2014: Ch. 16: Northeast. Climate Change Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program, 16-1-nn.

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