The Intergovernmental Panel on Climate Change (IPCC) was convened as an international group of experts who were charged with the task of evaluating whether human impacts on the environment were resulting in global climate change. In February 2007, the IPCC released its 4th Annual Assessment of Climate Change, Climate Change 2007, that indicated that in fact, it is almost certain that human actions are causing the earth’s climate to warm.
According to Climate Change 2007, there is about a 9 out of 10 chance of this. The human activities that are causing global warming include burning fossil fuels, changes in land use, and agriculture. Burning fossil fuels like oil, gas, and coal is releasing greenhouses gases into the atmosphere. Land use changes are decreasing the amount of plants that take greenhouse gases out of the atmosphere. And agriculture is releasing greenhouse gases like methane and nitrous oxide.
This is causing air and oceans to warm. Snow and ice in Earth’s polar regions melts. Sea level rises because of warmer oceans and the added water from melting glaciers and snow. Many effects of global warming have been seen over the past few decades. Arctic temperatures have risen at twice the rate of the global average in the past century. The amount of precipitation in different regions of the world has changed, and so have aspects of extreme weather events such as droughts, heat waves, and the intensity of hurricanes and typhoons.
According to computer models, whose results were summarized in the IPCC report, more global warming is in our future. For the next two decades global warming of about 0.2°C (0.36°F) is projected. If we continue to emit as many, or more, greenhouse gases, this will cause more warming during the 21st century than we saw in the 20th century. During the 20th century Earth’s average temperature rose 0.6°C (1.0 °F). During the 21st century, various computer models predict that Earth’s average temperature will rise between 1.8 and 4.0°C (3.2 to 7.2°F).
Read the complete Climate Change 2007, 4th Annual Assessment of Climate Change, at IPCC.
