National Climate Assessment Summarizes Climate Changes by Region

Climate, Forests and Woodlands August 26, 2015 Print Friendly and PDF

Adapted by Melanie Lenart, University of Arizona. Reviewed by Susan E. Moore and Mark A. Megalos, North Carolina State University. Full report of the National Climate Assessment is accessible online at:

Why it's important:

The National Climate Assessment of 2014, summarizes recent climate change and its effects by region.

  • Documents effects on the environment, society and forests,

  • Provides regional projections for future changes and their (Melillo et al. 2014).

  • Highlights adaptation and mitigation efforts that could help reduce the projected extent and impacts of climate change.

Key Findings:

IT’S HEATING UP! Globally, average annual temperature increased about 1.5 degrees Fahrenheit between 1880 and 2012. Much of this increase has been associated with a corresponding increase in greenhouse gases, such as carbon dioxide, that help trap heat in the Earth’s atmosphere (Figure 1).

Figure 1. Red bars show temperatures above the long-term average, and blue bars indicate temperatures below the long-term average. The black line shows atmospheric carbon dioxide (CO2) concentration in parts per million (ppm). (Figure source: .)


IMPACTS VARY: The ongoing temperature rise has played out in different ways around the country, both in temperature increases (Figure 2) and effects. These effects, past and future are summarized in the National Climate Assessment, along with observations and projections for the country and its various sectors and regions.

Figure 2. Temperature changes over the past 22 years (1991-2012) compared to the 1901-1960 average, and compared to the 1951-1980 average for Alaska and Hawai‘i. The black lines delineate the different regions. The bars on the graphs show the average temperature changes by decade for 1901-2012 (relative to the 1901-1960 average) for each region. The far right bar in each graph (2000s decade) includes 2011 and 2012. (Figure source: Kenneth Kunkel, Cooperative Institute for Climate and Satellites, NOAA NCDC).


WET Getting Wetter, Dry Getting Dryer While most of the country has seen a general increase in precipitation (Figure 3), Arizona and a few other states or areas in the Southeast have seen decreases in general. Very heavy precipitation events—those that formerly represented the top 1 percent in intensity—increased everywhere except the Hawaiian islands, including by 37 percent in the Midwest and 71 percent in the Northeast (Figure 4).

Figure 3. Total precipitation changes for 1991-2012 compared to the 1901-1960 average, and show wetter conditions in most areas. (Figure Source:


Figure 4. Percent increases in the amount of precipitation falling in very heavy events from 1958 to 2012 for each region of the continental United States. (Figure source: ).


More than 300 experts working as a team produced the National Climate Assessment, with guidance from a 60-member NCA committee. Decision makers from public and private sectors, researchers and resource managers all provided input to the report, including in 70 workshops and listening sessions held across the country.

Each region also has more detailed reports, but the summaries used here came from the highlights each regional team submitted to the national report. Links to websites and reports with more details are provided under each regional heading.

Figures 2-4 contain lines showing how states delineate into different regions. The regions are described below, with an emphasis on how climate change affects forests:


U.S. forests capture about 16 percent of carbon dioxide annually (range is between 7 and 24 percent.) Wetter Pacific Coast and Southeast forests absorb considerably more than arid or colder forests (Figure 5). Expanding urban development and agriculture threaten to reduce some of the capacity of U.S. forests to absorb the greenhouse gas in the future, as do wildfires and insect infestations that are likely to worsen under warming climate.

Figure 5. Average forest growth as measured by measured by net primary production from 2000 to 2006.  NPP is a measure of tree vigor and ability to lock up(sequester Carbon dioxide). (Figure source: adapted from: A Continuous Satellite-Derived Measure of Global Terrestrial Primary Production, Running et al. 2004).

Still, the capacity of forests to absorb some of the emissions contributing to climate change makes them a potential tool for offsetting future emissions. Additional mitigation efforts would be needed to cut the projected warming by century’s end roughly in half for the U.S.

The role of forests becomes crucial in coming decades, especially as water scarcity increases. As precipitation become more extreme, especially in the eastern half of the country (Figure 4), inland forests and forested coastal wetlands can absorb additional rainfall and sea level incursions, storing moisture during wet periods and releasing it during dry periods. The shade and other cooling features from rural and urban forests also help reduce heating as the planet warms up.

An increase in wildfires and insect infestations, projected for most regions, could reduce the capacity of the nation’s forests to continue absorbing carbon dioxide from fossil fuel emissions as they have in the past. However, management options exist that can help make U.S. forests more resilient in the face of changing climate.



Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. Yohe, Eds. 2014: Climate Change Impacts in the United States: The Third National Climate Assessment. U.S. Global Change Research Program, 841 pp. Accessible online at:

Running, S.W., R.R. Nemani, F.A. Heinsch, M. Zhao, M. Reeves, and H. Hashimoto, 2004. A Continuous Satellite-Derived Measure of Global Terrestrial Primary Production. Bioscience, DOI: 10.1641/0006-3568(2004)054[0547:ACSMOG]2.0.CO;2.

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This work is supported by the USDA National Institute of Food and Agriculture, New Technologies for Ag Extension project.