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 carbon dioxide and other greenhouse gasses 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 changes, such as a predicted rise in sea level, will take even longer to happen.
There is ample 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."
The Kyoto Protocol was agreed by the United Nations Framework Convention on Climate Change Parties in Kyoto, Japan, in December 1997. The Kyoto Protocol commits industrialized countries to achieve quantified targets for decreasing their emissions of greenhouse gases. In aggregate, the developed countries committed to reducing their overall emissions of six greenhouse gases by some 5% below 1990 levels over the period between 2008 and 2012, with specific targets varying by country.
The Kyoto Protocol has, for the first time, placed a constraint on the amount of greenhouse gases that will be allowed in developed countries in the period 2008-2012. Once it enters into force, developed countries will have binding commitments to reduce their greenhouse gas emission levels in the period 2008-2012.
The Kyoto Protocol also established several mechanisms to make it easier to reduce greenhouse gas emissions: the Clean Development Mechanism, Joint Implementation, and International Emissions Trading. In essence, these mechanisms enable countries to pay for emission reductions anywhere on the planet. Because climate change is a global problem, the location of the greenhouse gas emission reductions does not affect the environmental effect – reductions are equally good for the climate no matter where they occur.
