An Introduction 


Global warming is the observed increase in the average temperature of the Earth's atmosphere and oceans in recent decades and its projected continuation into the future. The decade of 2001-2009 was the warmest decade recorded on earth.

Global average near-surface atmospheric temperature rose 0.6 ± 0.2 °Celsius (1.1 ± 0.4 °Fahrenheit) in the 20th century. The prevailing scientific opinion on climate change is that "most of the warming observed over the last 50 years is attributable to human activities." The main cause of the human-induced component of warming is the increased atmospheric concentration of greenhouse gases (GHGs) such as carbon dioxide (CO2), which leads to warming of the surface and lower atmosphere by increasing the greenhouse effect. Greenhouse gases are released by activities such as the burning of fossil fuels, land clearing, and agriculture.

Models referenced by the Intergovernmental Panel on Climate Change (IPCC) predict that global temperatures may increase by 1.4 to 5.8 °C (2.5 to 10.5 °F) between 1990 and 2100. The uncertainty in this range results from both the difficulty of predicting the volume of future greenhouse gas emissions and uncertainty about climate sensitivity.

An increase in global temperatures can in turn cause other changes, including a rising sea level and changes in the amount and pattern of precipitation. These changes may increase the frequency and intensity of extreme weather events, such as floods, droughts, heat waves, hurricanes, and tornados. Other consequences include higher or lower agricultural yields, glacier retreat, reduced summer streamflows, species extinctions and increases in the ranges of disease vectors. Warming is expected to affect the number and magnitude of these events; however, it is difficult to connect particular events to global warming. Although most studies focus on the period up to 2100, even if no further greenhouse gases were released after this date, warming (and sea level) would be expected to continue to rise since CO2 has a long average atmospheric lifetime.

Remaining scientific uncertainty comes from the exact degree of climate change expected in the future and particularly how changes will vary from region to region across the globe. In addition, the complexity of the earth's climate complicates the understanding and forecasting of the effects of climate change. For example, changes in water vapor in the earth's atmosphere is believed to have cancelled roughly 25% of the global warming caused by carbon emissions during the past decade.

Most national governments have committed to taking steps to mitigate future climate change.

Read more about Climate Change from the U.S. Environmental Protection Agency

National Oceanic and Atmospheric Administration: GW Frequently Asked Questions

New York Times Global Warming Coverage

New Scientists Guide to Climate Change

Pew Center on Global Climate Change

Climate Change: American Museum of Natural History


        © 2007 by Bruce Gourley. All rights reserved.