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Climate Change and Variability

Ten Indicators of a Warming World Image

A warmer climate means higher sea level, humidity, and temperatures of the air and ocean. A warmer climate also means less snow cover, increased melting Arctic sea ice during the summer, and shrinking glaciers. Visit Ten Signs of a Warming World, to learn more about these indicators.

According to the Global Climate Change Impacts in the United States report, "Observations show that warming of the climate is unequivocal. The global warming observed over the past 50 years is due primarily to human-induced emissions of heat-trapping gases."

The Global Climate Change Impacts in the United States report is the authoritative scientific report, developed by 13 Federal agencies, which summarizes the state of the science and the impacts of climate change on the United States, now and in the future. The Global Climate Change Impacts in the United States 2009 Report is the latest published edition of this report under the authority of the United States Global Change Research Program. The next edition of this report is scheduled to be released in 2014.

Global Climate Change Impacts in the United States 2009 Report Key Findings

  • Global warming is unequivocal and primarily human induced.
  • Climate changes are underway in the United States and are projected to grow.
  • Widespread climate-related impacts are occurring now and are expected to increase.
  • Climate change will stress water resources.
  • Crop and livestock production will be increasingly challenged.
  • Coastal areas are at increasing risk from sea level rise and storm surge.
  • Risks to human health will increase.
  • Climate change will interact with many social and environmental stresses.
  • Thresholds will be crossed, leading to large changes in climate and ecosystems.
  • Future climate change and its impacts depend on choices made today. 

See Global Climate Change Impacts in the United States Highlights for further information regarding these key findings.

See the Intergovernmental Panel on Climate Change for more in-depth information on climate change and to view various assessments and technical reports.

For general information on climate and climate change, visit

Climate Change and Extremes

See Changes in Heat Waves, Cold Waves, Floods, and Droughts in the United States for more information on these extremes and scientists’ collective state of knowledge.

See Analyses of Maximum Precipitation Estimates: Impacts of a Wetter Future for more information on a recent report about rising atmospheric concentrations of greenhouse gases and their effects on extreme precipitation events.

See NOAA’s Atlantic Hurricanes, Climate Variability, and Global Warming Fact Sheet for a summary and assessment on the relationship between Atlantic hurricanes and climate change.

See the Special Report on Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation to learn more about policies to avoid, prepare for, respond to, and recover from the risks of extreme events.