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The Intergovernmental Panel on Climate Change (IPCC), a multi-national scientific body set up by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP), defined climate change in its Nov. 2007 Fourth Assessment Report of Cliamte Change 2007 as the following:
"Climate change refers to a change in the state of the climate that can be identified (e.g., by using statistical tests) by changes in the mean and/or the variability of its properties, and that persists for an extended period, typically decades or longer. Climate change may be due to natural internal processes or external forcings, or to persistent anthropogenic changes in the composition of the atmosphere or in land use. Note that the Framework Convention on Climate Change (UNFCCC), in its Article 1, defines climate change as: ‘a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods’. The UNFCCC thus makes a distinction between climate change attributable to human activities altering the atmospheric composition, and climate variability attributable to natural causes."
The US Environmental Protection Agency (EPA), in a section of its website, www.epa.gov, on climate change titled "Basic Information" (accessed Dec. 3, 2008), defined climate change as the following:
"The term climate change is often used interchangeably with the term global warming, but according to the National Academy of Sciences, 'the phrase 'climate change' is growing in preferred use to 'global warming' because it helps convey that there are [other] changes in addition to rising temperatures.'
Climate change refers to any significant change in measures of climate (such as temperature, precipitation, or wind) lasting for an extended period (decades or longer). Climate change may result from:
natural factors, such as changes in the sun's intensity or slow changes in the Earth's orbit around the sun;
natural processes within the climate system (e.g. changes in ocean circulation);
human activities that change the atmosphere's composition (e.g. through burning fossil fuels) and the land surface (e.g. deforestation, reforestation, urbanization, desertification, etc.)
Global warming is an average increase in the temperature of the atmosphere near the Earth's surface and in the troposphere, which can contribute to changes in global climate patterns. Global warming can occur from a variety of causes, both natural and human induced. In common usage, 'global warming' often refers to the warming that can occur as a result of increased emissions of greenhouse gases from human activities."
The National Oceanic and Atmospheric Administration (NOAA), in a section of its website, www.noaa.gov, titled "Observing Climate Variability and Change" (accessed Dec. 3, 2008), provided the following definition:
"The Earth's climate is dynamic and naturally varies on seasonal, decadal, centennial, and longer timescales. Each 'up and down' fluctuation can lead to conditions which are warmer or colder, wetter or drier, more stormy or quiescent. Analyses of decadal and longer climate records and studies based on climate models suggest that many changes in recent decades can be attributed to human actions; these decadal trends are referred to as climate change. The effects of climate variability and change ripple throughout the environment and society - indeed touching nearly all aspects of the human endeavor and the environment...
...The amount of energy entering and escaping from Earth is the determining factor in climate. Any changes to that balance-either the input or the output-will cause a directional change in climate. Observations have conclusively demonstrated that the atmospheric abundance of greenhouse gases has risen dramatically since the onset of the Industrial Age. Human activities such as fossil fuel burning and deforestation have caused this increase. The atmospheric concentration of carbon dioxide (CO2 ), has risen by 31% since 1750 and is now at the highest concentration seen in the last 420,000 years (and likely higher than any concentration seen for the last 20 million years). Other greenhouse gases that have increased since 1750 are methane (up by 151%), nitrous oxide (up by 17%), halocarbons (rising rapidly since 1950 but slowing or decreasing in recent years because of international agreements to protect the ozone layer), and tropospheric ozone (up by 36%). These gases absorb heat that would otherwise escape to space."