…The Earth's surface is kept warm because of greenhouse gases, which let light through but retain heat. As a result, Earth's surface temperature is considerably higher than if no such gases were present. From physics we know that without greenhouse gases in the atmosphere the average surface temperature of our planet would be -18°C. The temperate zones would be uninhabitable: even the tropics would be freezing.

Each year since the mid-nineteenth century, we have been burning billions of tonnes of fossil fuels, as well as destroying forest through slash-and-burn techniques. As the carbon in the fuel is burnt carbon dioxide is released, which is a greenhouse gas like other atmospheric gasses such as methane and most importantly, water vapour. That means we are contributing to the levels of natural greenhouse gasses, as well as adding some of our own, such as CFC's (chlorofluorocarbons). The total amounts of carbon dioxide that we have added to the atmosphere are staggering: 190 billion tonnes over the past fifty years. In that period we have emitted three times the carbon dioxide released by mankind over rest of time put together. Since World War II alone we have increased the level of carbon dioxide by nearly one quarter. Not all that carbon dioxide has stayed there. Approximately half appears to have left the atmosphere, absorbed into the oceans, soils and perhaps even buried in sediments. We are lucky that so much has gone from the atmosphere but maybe wrong to assume the natural sink will always operate effectively to limit the damage we are imposing…