Attribution of recent climate change
Climate change is a long-term change in the statistical distribution of weather patterns over periods of time that range from decades to millions of years. It may be a change in the average weather conditions or a change in the distribution of weather events with respect to an average, for example, greater or fewer extreme weather events. Climate change may be limited to a specific region, or may occur across the whole Earth.
In recent usage, especially in the context of environmental policy, climate change usually refers to changes in modern climate. It may be qualified as anthropogenic climate change, more generally known as global warming or anthropogenic global warming (AGW).
Factors that can shape climate are climate forcings. These include such processes as variations in solar radiation, deviations in the Earth's orbit, mountain-building and continental drift, and changes in greenhouse gas concentrations. There are a variety of climate change feedbacks that can either amplify or diminish the initial forcing. Some parts of the climate system, such as the oceans and ice caps, respond slowly in reaction to climate forcing because of their large mass. Therefore, the climate system can take centuries or longer to fully respond to new external forcings.
Attribution of recent climate change is the effort to scientifically ascertain mechanisms responsible for recent changes observed in the Earth's climate. The effort has focused on changes observed during the period of instrumental temperature record, when records are most reliable; particularly on the last 50 years, when human activity has grown fastest and observations of the troposphere have become available. The dominant mechanisms to which recent climate change has been attributed all result from human activity. They are:
- increasing atmospheric concentrations of greenhouse gases
- global changes to land surface, such as deforestation
- increasing atmospheric concentrations of aerosols.
Attribution of recent change to anthropogenic forcing is based on the following facts:
- The observed change is not consistent with natural variability.
- Known natural forcings would, if anything, be negative over this period.
- Known anthropogenic forcings are consistent with the observed response.
- The pattern of the observed change is consistent with the anthropogenic forcing.
Climate change denial is a term used to describe organized attempts to downplay, deny or dismiss the scientific consensus on the extent of global warming, its significance, and its connection to human behavior, especially for commercial or ideological reasons. Typically, these attempts take the rhetorical form of legitimate scientific debate, while not adhering to the actual principles of that debate. Climate change denial has been associated with the energy lobby, industry advocates and free market think tanks, often in the United States. Some commentators describe climate change denial as a particular form of denialism. The term is rarely used by those to whom it is applied.
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