Global climate change has already had observable effects on the environment. Glaciers have shrunk, ice on rivers and lakes is breaking up earlier, plant and animal ranges have shifted and trees are flowering sooner.
Effects that scientists had predicted in the past would result from global climate change are now occurring: loss of sea ice, accelerated sea level rise and longer, more intense heat waves.
Scientists have high confidence that global temperatures will continue to rise for decades to come, largely due to greenhouse gasses produced by human activities. The Intergovernmental Panel on Climate Change (IPCC), which includes more than 1,300 scientists from the United States and other countries, forecasts a temperature rise of 2.5 to 10 degrees Fahrenheit over the next century.
According to the IPCC, the extent of climate change effects on individual regions will vary over time and with the ability of different societal and environmental systems to mitigate or adapt to change.
The IPCC predicts that increases in global mean temperature of less than 1.8 to 5.4 degrees Fahrenheit (1 to 3 degrees Celsius) above 1990 levels will produce beneficial impacts in some regions and harmful ones in others. Net annual costs will increase over time as global temperatures increase.
"Taken as a whole," the IPCC states, "the range of published evidence indicates that the net damage costs of climate change are likely to be significant and to increase over time."
Below are some of the regional impacts of global change forecast by the IPCC:
Global Climate Change: Recent Impacts
|Phenomena||Likelihood that trend occurred in late 20th century|
|Cold days, cold nights and frost less frequent over land areas||Very likely|
|More frequent hot days and nights||Very likely|
|Heat waves more frequent over most land areas||Likely|
|Increased incidence of extreme high sea level *||Likely|
|Global area affected by drought has increased (since 1970s)||Likely in some regions|
|Increase in intense tropical cyclone activity in North Atlantic (since 1970)||Likely in some regions|
* Excluding tsunamis, which are not due to climate change.
Global Climate Change: Future Trends
|Phenomena||Likelihood of trend|
|Contraction of snow cover areas, increased thaw in permafrost regions, decrease in sea ice extent||Virtually certain|
|Increased frequency of hot extremes, heat waves and heavy precipitation||Very likely to occur|
|Increase in tropical cyclone intensity||Likely to occur|
|Precipitation increases in high latitudes||Very likely to occur|
|Precipitation decreases in subtropical land regions||Very likely to occur|
|Decreased water resources in many semi-arid areas, including western U.S. and Mediterranean basin||High confidence|
For more information, visit NASA's website on Climate Change.