Earth's mean surface temperature has increased by about 0.8 °C with about two-thirds of the increase occurring since 1980.

Earth's mean surface temperature has increased by about 0.8 °C with about two-thirds of the increase occurring since 1980.Climate model projections are summarized in the 2007 Fourth Assessment Report (AR4) by the Intergovernmental Panel on Climate Change (IPCC). They indicate that during the 21st century the global surface temperature is likely to rise a further 1.1 to 2.9 °C for their lowest emissions scenario and 2.4 to 6.4 °C for their highest.

Global warming has become perhaps the most complicated issue facing world leaders.

Global warming has become perhaps the most complicated issue facing world leaders. Warnings from the scientific community are becoming louder, as an increasing body of science points to rising dangers from the ongoing buildup of human-related greenhouse gases — produced mainly by the burning of fossil fuels and forests.