Climate change basics
This is only a very brief introduction on climate change science, please visit the Climate Change Resource Center (CCRC) FAQs page for more information.
The Greenhouse Effect
The greenhouse effect is a naturally occurring process that is necessary to maintain the Earth at a suitable temperature for life. In fact, without the greenhouse gas effect, the temperature of the Earth would be about zero degrees Fahrenheit. The sun emits energy in the form of short-wave radiation. About 30% of the energy from the sun is reflected back into space by the atmosphere and clouds. The remaining energy is absorbed by clouds, atmospheric particles, and the surface of the Earth. In turn, the Earth emits long-wave infrared radiation into the atmosphere. Some of the radiation from the Earth passes through the atmosphere into space, but most of the radiation is absorbed by greenhouse gases. Some important greenhouse gases are water vapor, carbon dioxide, methane, and nitrous oxide
Increases in greenhouse gases add to the natural greenhouse gas effect. Carbon dioxide is the one of the most important greenhouse gas. Human activities, like fossil fuel use and deforestation, are a large source of carbon dioxide emissions. Since 1750, carbon dioxide in the atmosphere has increased 30% from 280 parts per million (ppm) to 370 ppm in 2005. Methane, another important greenhouse gas, has also increased from human activities, rising from 715 parts per billion (ppb) in 1750 to 1,774 ppb in 2005. Long-term data demonstrate that atmospheric concentrations of both carbon dioxide and methane are currently higher than at any other time in the past 650,000 years, and these gases influence global warming more than other greenhouse gases.
The increases in greenhouse gases, which amplify the greenhouse effect, lead to global warming and changes in climate. Average temperatures around the world are 1.4°F (0.8°C) greater than they were in 1880 and the rate of warming has doubled since 1950. In 2007, the Intergovernmental Panel on Climate Change (IPCC) issued its fourth report on climate change, providing a definitive statement that global warming has occurred and will continue to change the climate. The IPCC continues its work on climate change, with the competition of a fifth assessment report expected by the end of 2014.
Is the Climate Cooling?
Recent controversy has arisen concerning trends of global temperatures from 1998 to 2009. Lines plotted through specific subsets of years during this period appear to have negative or flat slopes, which has led to people asserting that global warming has slowed, stopped, or reversed since 1998. Trends over such a short period should be interpreted with great caution,because meaningful global trends need to be calculated over at least two or three decades in order to account for natural warming and cooling of the Earth’s climate. Global mean temperature can increase or decrease from year to year because of volcanic eruptions, solar activity, and large-scale ocean circulation patterns like the El Niño Southern Oscillation. There are several instances in the temperature record since 1880 where 5 to 10 year trends appear flat, or even negative, and there was a long, level period during the 1940s to 1970s. Nonetheless, the overall trend has been positive, and recent decades are clearly warmer than previous decades. Considering information from multiple years, datasets, and organizations, there is no valid statistical evidence for global cooling, and the weight of evidence still supports the long-term trend of global warming.
- U.S. Environmental Protection Agency (EPA): Climate Change
- Intergovernmental Panel on Climate Change (IPCC)
- NASA Earth Observatory
- U.S. Department of Agriculture, Forest Service
- Climate Change Resource Center
- Research & Development - Climate Change
- Forest Management for an Uncertain Climate Future: Tools and Training
- National Roadmap for Responding to Climate Change
- The US Forest Service’s Strategic Framework for Responding to Climate Change (pdf)
- A Performance Scorecard for Implementing the Forest Service Climate Change Strategy (pdf)
- Pew Center on Global Climate Change
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Last Modified: 08/02/2017