Climate change impacts in the United States

Climate change impacts in the United States - what the IPCC 4th Assessment Report has found:
  • Increases in the population of intense hurricanes in 2005 created record catastrophe losses, principally in the Gulf Coast US and in Florida, when a record four Saffir Simpson severe (Cat3-5) hurricanes made landfall causing more than US$100 billion in damages with almost 2000 fatalities []. 
  • Droughts: Due to dry and unusually warm summers related to warming of western tropical Pacific and Indian Oceans in recent years (1998- 2004) in Western United States [ & 14.2.1]. Western USA: Semi-arid and arid areas will suffer a decrease of water resources due to climate change [3.4, 3.7].
  • Projected Columbia River seasonal flows shift markedly toward larger winter and spring flows and smaller summer and fall flows. A 2°C warming in the 2040s would increase demand for water in Portland, Oregon by 5.7 million m3/yr with an additional demand of 20.8 million m3/yr due to population growth, while decreasing supply by 4.9 million m3/yr [Box 14.2]
  • Net primary production (NPP) in the continental U.S. increased nearly 10% from 1982-1998. Overall forest growth in North America will likely increase modestly (10-20%) as a result of extended growing seasons and elevated CO2 over the next century. In the mid latitudes changes in NPP are depending on whether there is sufficient enhancement of precipitation to offset increased evapotranspiration in a warmer climate [14.2.2].
  • Streamflow peaks in the snowmelt-dominated western mountains occurred 1-4 weeks earlier in 2002 than in 1948 [14.2.1]. Decrease of number of ski areas from 58 to 17 in New Hampshire (1975-2002) []. Projected warming in the western mountains by the mid 21st Century is very likely to cause large decreases in snowpack, earlier snowmelt, more winter rain events, increased peak winter flows and flooding, and reduced summer flows [14.4.1].
  • Nutritional stresses related to longer ice-free seasons in the Beaufort Sea (Alaska) may be inducing declining survival rates, smaller size, and cannibalism among polar bears []. The Pika, a small mammal in western mountains, has been extirpated from many mountain slop (climate-driven extinction) []. Expected 8% loss freshwater fish habitat, 9% loss of salmon with temperature increase of 1.3°C above pre-industrial levels [Table 4.1].
  • A landward migration of mangroves into adjacent wetland communities has been recorded in the Florida Everglades during the past 50 years, apparently responding to sea-level rise over that period [ &]. 
  • Regionally losses of coastal vegetated wetlands expected to be most severe on the Atlantic and Gulf of Mexico coasts of North and Central America []. Present rates of coastal wetland loss are projected to increase with accelerated sea level rise (in part due to structures preventing landward migration) [14.4.3]. 
  • Wetland changes: Decreases in salt marsh area due to regional sea level rise and human impacts (1920s-1999) Long Island, NY; Connecticut, []. Landward migration of cord grass (Spartina alterniflora) due to sea level rise and excess nitrogen (1995-1999); late 20th century Rhode Island [].
  • Treelines have markedly shifted to higher elevations during the 20th century in Alaska []. Arctic-alpine species decline in Montana at the southern margin of range (due to increased temperature) [].
  • West: Lilac, honeysuckle flowering 1.5-3.5 days/decade earlier (1957-1994) []. Northeast: Lilac flowering/leaf-unfolding 3.4/2.6 days/decade earlier (1965-2001 ) []. Washington, DC, 100 plant species flowering 0.8 days/decade earlier (1970-1999) []. Massachusetts spring arrival of 52 bird species 0.8 later to 9.6 days/ decade earlier (1932-1993) []. California coast spittlebug northward range shift (due to increased temperature) [] Washington State: Skipper Butterfly range expansion with increased min. temperature [].
Florida Keys, Florida, United States of America. 
Florida Keys, Florida, United States of America.

WWF work

What WWF is doing on the ground in the US to protect against climate change:

WWF contacts

  • David Aplin

    Senior Program Officer

    WWF United States,
    Washington DC

    +1 907 279 5504

  • Miriam Geitz

    Senior Conservation Officer


    +47 22 00 65 03

Climate Witnesses

WWF runs the Climate Witness programme to collect people's local observations of climate change that are then verified by scientists.
Long time farmers Steve and Linnea Bensel are the owners of Nootka Rose Farm, located in the San Juan Islands of Washington state. During the past several years they have become increasingly aware of the variability in weather patterns and of a shift to warmer temperatures.
Steve and Linnea Bensel, WWF Climate Witnesses from US<br>© Linnea Bensel

Nola Royce, a personal trainer and fitness instructor, has been hiking and climbing in the northeastern USA for over 30 years. The loss of glaciers worldwide greatly concerns her.
Nola Royce, WWF Climate Witness from US<br>© Nola Royce

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