Over the past 200 years, its concentration in the air has risen by a third, largely because growing populations have burnt more trees and failed to replace them and because they have begun to burn massive quantities of fossil fuels. If we carry on as we are, there will be twice as much CO2 in the atmosphere by late next century. And the heating power of the sun at the earth's surface will rise by about 4 watts per square metre to 240 watts. Not a lot, you might think. What is uncertain is how much the changes in the planet caused by warming will themselves amplify that warming.
Most solar heat reaching polar regions is reflected from the white ice right back into space.
If we melt some of the ice caps, less heat will be reflected. Global warming will also evaporate more water from the oceans into the air. Water vapour is the most important greenhouse gas of all. So again, extra warming is likely. Scientists have warned for some time that the polar regions may be the first to show signs of global warming just as they were for the thinning ozone layer.