2. What is Climate Change?

Link to further info: http://unfccc.int/text/resource/iuckit/fact01.html

The earth's climate is driven by energy from the sun. About 30% is immediately scattered back into space, but most of it passes down through the atmosphere to warm the earth's surface. The earth throws off heat as well as absorbing it, but greenhouse gases in the atmosphere prevent it from escaping directly from the surface to space. This is because the earth gives off heat as infrared radiation, which cannot pass straight through the air like the energy from the sun which arrives in the form of visible light and passes easily through the atmosphere. Greenhouse gases trapping heat in the atmosphere produces a "natural greenhouse effect" that keeps the planet some 30oC warmer than it would be otherwise, which is essential for life as we know it.

Levels of all key greenhouse gases (with the possible exception of water vapour) are rising as a direct result of human activity. Emissions of carbon dioxide (mainly from burning coal, oil, and natural gas), methane and nitrous oxide (due to agriculture and changes in land use), ozone (generated by the fumes in automobile exhausts) and CFCs (manufactured by industry) are changing how the atmosphere absorbs energy. This is all happening at an unprecedented speed. The result is known as the "enhanced greenhouse effect".

The result is a "global warming" of the earth's surface and lower atmosphere accompanied by many other changes such as changes in cloud cover and wind patterns. Climate models predict that the global average temperature will rise by about 2oC (3.6oF) by the year 2100 if current emission trends continue. Because there are still many uncertainties, current estimates of how much it will warm during the 21st century range from 1 to 3.5oC.

Past emissions have already committed us to some climate change. The climate does not respond immediately to emissions. It will therefore continue to change for many years even if greenhouse gas emissions are reduced and atmospheric levels stop rising. Some important climate change impacts (2.1), such as a predicted rise in sea level, will take even longer to be fully realized.

There is evidence that climate change has already begun. The pattern of temperature trends over the past few decades resembles the pattern of greenhouse warming predicted by models. While many uncertainties remain, scientists believe that "the balance of the evidence suggests a discernible human influence on global climate."