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What causes climate change?

Greenhouse gases (GHG) such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in Earth’s atmosphere trap heat that would otherwise escape into space, causing global warming or climate change. They act a bit like wearing a sweater on a warm day, letting heat from the sun in, but not letting much of your heat out. Although these gases can be found in nature, we have been releasing them into the atmosphere at unprecedented rates through  combustion of coal, oil, and natural gas for energy; deforestation; and maintaining large populations of ruminant livestock. Once in the atmosphere, heat-trapping gases remain there for many years – for example CO2 lasts about 100 years.

Atmospheric concentration of CO2 has increased from the 1850 pre-industrial level of 280 parts per million (ppm) to over 400 ppm, and the concentration continues to increase at about 2 ppm per year. CH4 and N2O exhibit similar trends and are estimated to account for about half of the currently observed global warming. Historically, over the 800,000 year climate record from Antarctic ice cores, GHG concentrations have correlated closely with temperature. CO2 concentrations over this period reached a maximum of 290 ppm. Current concentrations of CO2 are almost 40% higher than previously observed.

Scientific consensus is unequivocal that Earth’s climate is warming, that climate change is predominantly human-caused, and that recent climatic change has had widespread impacts on human as well as natural systems. Among other impacts, observed consequences of climate change include substantial loss of ice in the Arctic, melting of the Greenland and Antarctic ice sheets, ocean acidification, sea level rise, and increased frequency of heat waves. According to the latest report of the United Nations Intergovernmental Panel on Climate Change,

“Continued emission of greenhouse gases will cause further warming and long-lasting changes in all components of the climate system, increasing the likelihood of severe, pervasive and irreversible impacts for people and ecosystems. Limiting climate change would require substantial and sustained reductions in greenhouse gas emissions which, together with adaptation, can limit climate change risks.”

For latest weekly average CO2 concentration at Mauna Loa visit

Post last edited on: 2014 November 05

Tags: background, causes

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