National Summary

The Overview of the Climate Change Impacts on the United States, produced by the National Assessment Synthesis Team, reviews previous impacts as well as future potential changes.

1. How will global climate change affect climate in the United States?

• Average Temperature: The temperature in the United States is projected to rise between 5 and 9 degrees Fahrenheit on average over the next 100 years. This increase is more than temperature changes over the last 10,000 years.
• Precipitation: More precipitation is likely over the United States, and more heavy downpours. The increase in temperature will likely increase evaporation (due to the water cycle) [evapotraspiration]. So, some areas could be drier. There could be more droughts as well as flash floods.

2. How will people and their surroundings be affected by these climate changes?

• Forests: The projected change in temperature and precipitation will affect forest ecosystems and the timber industry, though impacts will differ across regions. Higher temperatures will enhance forest productivity, while droughts will reduce productivity. Hardwoods could become more prevalent. There also could be increased risk of forest fires and more intense levels of pests.
• Fresh water quantity and water ecosystems: Higher temperatures and levels of precipitation will increase evaporation; some regions could experience more variability in precipitation. These impacts influence the amount of runoff as well as drought and flood conditions, affecting the water available for human use and ecosystems.
• Costal Zones: Sea-level rise and more storm surges are the biggest factor for costal zones, where some low-level beaches, islands, marshes and costal forests could disappear. Sea-level rise and storm surges also will affect the infrastructure and living conditions for humans in costal areas.
• Humans: Increased temperatures could lead to more heat-related illnesses in summers. Higher temperatures also could lead to increased “air pollution, injuries and deaths from extreme weather events and diseases carried by water, food, insects, ticks and rodents.” Humans will have to adapt to these changes.
• Agriculture: US agriculture production overall is expected to benefit from climate change. However, producers will need to be prepared for increases in extreme weather events, pests, weeds and possibly lower prices as supply increases.

3. How is this information useful?
There are substantial opportunities to minimize the negative impacts and maximize the benefits of climate change through adaptation. Examples include cultivating varieties of crops, trees, and livestock that are better suited to hotter conditions. The National Summary report includes an initial identification of potential adaptation strategies, but not an analysis of their effectiveness, practicality and costs.

4. What are the regional impacts?
Across the United States, climate will change, but the intensity of the change depends on the region and its characteristics. The Northeast can expect changes in precipitation. Some of this will be in the form of heavy rainfall and increased flooding; changes in the “intensity and frequency of hurricanes are a major concern” (Overview, p. 42)

Climate change will likely add to the stresses incurred by the Northeast's wetlands, bays and estuaries, including the Chesapeake Bay, because of higher water temperature and potential changes in precipitation and water runoff.

These impacts could lead to changes in area transportation, power, and water supply systems, as they adapt across the Northeast. As humans adapt, there also could be changes in their recreation patterns.(Overview, p.44)

Warmer winters might affect the population of ticks and the occurrences of Lyme disease and other "vector-borne" diseases, requiring that modern medicine continue to adapt practices as has happened in the past. (Overview, p.45) "Key concerns involve the potential for changes in pest types and populations, invasive species and in key species that are truly characteristic of a region or are of economic significance.”

Other Regions: http://www.usgcrp.gov/usgcrp/Library/nationalassessment/4IntroD.pdf.