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Climate change is one of the greatest environmental, social and economic threats facing our planet.

During the 20th century, the Earth’s average surface temperature rose by around 0.7°C. The overwhelming consensus of scientists, including myself, is that much of this global warming, and particularly the rapid increase that has occurred over the last 30 years, is attributable to human activities. In its Third Assessment Report, published in 2001, the Intergovernmental Panel on Climate Change (IPCC) projected that global average surface temperatures will rise a further 1.4 to 5.8°C by the end of this century. Temperature increases above the low end of this range are highly likely to cause significant impacts to humans and other species while profoundly changing the world's climate.

Scientific research has provided strong evidence for human-induced climate change through a variety of methods, and studies in all regions of the world continue to define the "spectrum of concern" about climate change and its current and future climate impacts. There is evidence that a variety of impacts are already attributable to climate change: changes in species behavior and lifecycle, rising sea levels, retreat of glaciers worldwide, and additional risks to human populations from heat-related impacts, to name a few. Impacts are expected to intensify and diversify as temperatures increase further.

Jackson Glacier

However, future projections of climate change and climate impacts are inherently uncertain, and often that uncertainty paralyzes decision making or is used as a reason to delay action. Uncertainty in forecasting of future conditions or events is an accepted aspect of a variety of political and financial decision making processes, and it should not prevent society from making policy decisions now to alter the trajectory of greenhouse gas emissions and climate change. Instead, we must recognize that, while there is uncertainty, we have enough information to begin to make educated guesses about how much we should reduce greenhouse gas emissions, and that the longer we delay, the more dangerous change becomes likely.

For more information, refer to my Links page, and, in particular:

http://stephenschneider.stanford.edu