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What We Do Know About Climate Change

Climate change science has come a long way in understanding the fundamentals of global warming. There is no doubt anymore in the mainstream scientific community that the Earth is warming, and increasing evidence shows that humans have a significant part in it.

We do know, for example, that certain gases, such as carbon dioxide and methane, play a crucial role in determining the Earth's climate by preventing heat from escaping the atmosphere. Researchers have also been able to document that the increased concentration of such gases in the atmosphere results from human activities such as the burning of fossil fuels, deforestation and land degradation, cattle ranching, and rice farming. The "fingerprint" of humans causing—at least in part—the global warming we now experience has been documented in a growing number of studies.

In the IPCC's 2001 assessment of the scientific basis of climate change, the experts draw three important conclusions:

  • Climate change is underway. Or in the IPCC's own words: "An increasing body of observations gives a collective picture of a warming world and other changes in the climate system."
  • Human activities do and will continue to alter the composition of the atmosphere. The IPCC states, "emissions of greenhouse gases and aerosols due to human activities continue to alter the atmosphere in ways that are expected to affect the climate." Adding that trends of greenhouse gas emissions from human activities point further upward, the scientists argue that significant emission reductions would be necessary to stabilize the climate.
  • Recent warming can be largely attributed to human causation. More strongly than ever, the IPCC states in its 2001 assessment, "There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities."

Climatologists—using ever-more sophisticated computer models—suggest that the planet will warm up over the next generations as a result of this growing concentration of heat-trapping gases in the atmosphere. While 20th century warming is already likely to be the largest during any century over the past 1,000 years for the Northern hemisphere, the anticipated warming over the 21st century represents a more rapid climate change than at any time in recorded history.

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