In order to ensure we protect natural and cultural resources in the future, we must begin planning for climate change impacts today. Some changes are already occurring. Other climate change impacts are expected in the coming decades. For example, heat waves in the United States are expected to become stronger and more frequent in the coming decades, threatening natural ecosystems and human quality of life.
Future changes will depend on many factors
The magnitude and rate of future climate change will primarily depend on the following factors:
- The rate at which levels of greenhouse gas concentrations in our atmosphere continue to increase
- How strongly features of the climate (e.g., temperature, precipitation, and sea level) respond to the expected increase in greenhouse gas concentrations
- Natural influences on climate (e.g., from volcanic activity and changes in the sun’s intensity) and natural processes within the climate system (e.g., changes in ocean circulation patterns)
Scientists use computer models of the climate system to better understand these issues and project future climate changes.
Past and present-day greenhouse gas emissions will affect climate far into the future
Many greenhouse gases stay in the atmosphere for long periods of time. As a result, even if emissions stopped increasing, atmospheric greenhouse gas concentrations would continue to increase and remain elevated for hundreds of years. Moreover, if we stabilized concentrations and the composition of today’s atmosphere remained steady (which would require a dramatic reduction in current greenhouse gas emissions), surface air temperatures would continue to warm. This is because the oceans, which store heat, take many decades to fully respond to higher greenhouse gas concentrations. The ocean’s response to higher greenhouse gas concentrations and higher temperatures will continue to impact climate over the next several decades to hundreds of years.
To learn more about greenhouse gases, please visit the EPA’s Greenhouse Gas Emissions page and the Greenhouse Effect section of the Causes of Climate Change page.
Key U.S. Projections
- By 2100, the average U.S. temperature is projected to increase by about 4°F to 11°F, depending on emissions scenario and climate model.
- An increase in average temperatures worldwide implies more frequent and intense extreme heat events, or heat waves. The number of days with high temperatures above 90°F is expected to increase throughout the United States, especially in areas that already experience heat waves. For example, areas of the Southeast and Southwest currently experience an average of 60 days per year with a high temperature above 90°F. These areas are projected to experience 150 or more days a year above 90°F by the end of the century, under a higher emissions scenario. In addition to occurring more frequently, these very hot days are projected to be about 10°F hotter at the end of this century than they are today, under a higher emissions scenario.
- Learn more.
Changes in Precipitation and Storm Events:
- Northern areas are projected to become wetter, especially in the winter and spring. Southern areas, especially in the West, are projected to become drier.
- Heavy precipitation events will likely be more frequent. Heavy downpours that currently occur about once every 20 years are projected to occur about every four to 15 years by 2100, depending on location.
- More precipitation is expected to fall as rain rather than snow, particularly in some northern areas.
- The intensity of Atlantic hurricanes is likely to increase as the ocean warms. Climate models project that for each 1.8°F increase in tropical sea surface temperatures the rainfall rates of hurricanes could increase by 6-18% and the wind speeds of the strongest hurricanes could increase by about 1-8%. There is less confidence in projections of the frequency of hurricanes, but the global frequency of tropical hurricanes is likely to decrease or remain essentially unchanged.
- Cold-season storm tracks are expected to continue to shift northward. The strongest cold-season storms are projected to become stronger and more frequent.
- Learn more.
Changes in Ice, Snowpack, and Permafrost
- Northern Hemisphere snow cover is expected to decrease by approximately 15% by 2100.
- Models project the snow season will continue to shorten, with snow accumulation beginning later and melting starting earlier. Snowpack is expected to decrease in many regions.
- Permafrost is expected to continue to thaw in northern latitudes. This would have large impacts in Alaska.
- Learn more.
Changes in Sea Levels
Regional and local factors will influence future relative sea level rise for specific coastlines around the world. For example, relative sea level rise depends on land elevation changes that occur as a result of subsidence (sinking) or uplift (rising). Assuming that these historical geological forces continue, a 2-foot rise in global sea level by 2100 would result in the following relative sea level rise:
- 2.3 feet at New York City
- 2.9 feet at Hampton Roads, Virginia
- 3.5 feet at Galveston, Texas
- 1 foot at Neah Bay in Washington state
Relative sea level rise also depends on local changes in currents, winds, salinity, and water temperatures, as well as proximity to thinning ice sheets. Learn more.
Changes in Ocean Chemistry
Ocean acidification adversely affects many marine species, including plankton, mollusks, shellfish, and corals. As ocean acidification increases, the availability of calcium carbonate will decline. Calcium carbonate is a key building block for the shells and skeletons of many marine organisms. If atmospheric CO2 concentrations double, coral calcification rates are projected to decline by more than 30%. If CO2 concentrations continue to rise at their current rate, corals could become rare on tropical and subtropical reefs by 2050. Learn more.
The following resources may help guide management and acquisition decisions, by providing information about predictions for climate change impacts in the future:
Learn about current climate change impacts that may already be affecting the conservation values of your protected land.