About 6 billion tons of CO2 are released into the atmosphere annually by the burning of fossil fuels. An additional 1-2 billion tons are introduced by the burning and logging of forests. These, among other sources, result in the overall increase of the amount of CO2 in the air. Since about 1860, the level has increased by about 30%.

Other greenhouse gases have also dramatically increased since pre-industrial times. For example, methane concentrations have doubled and nitrous oxide levels have risen by 15%. The overall emission of greenhouse gases is growing by about 1 percent per year. Over the last 160,000, a clear correlation has been tied with levels of greenhouse gases such as carbon dioxide and temperature change (see chart). While it is still unclear whether the increased carbon dioxide emission directly lead to the rise of temperature or vice versa (the old chicken and the egg question), scientists have clearly shown a link between greenhouse gas concentrations and temperature fluctuations.

Even over the past 100 years there has been a noticeable increase in the global average temperature. The eleven warmest years of this century have all occurred since 1980. Although a one degree Fahrenheit change over a century might not sound like a great deal, the near term projections of a large change over a very small amount of time is cause for concern.

Reprinted from Climate Change, State of Knowledge --OSTP