Temperatures in the northern hemisphere passed the limit of 2 degrees of warming for the first time last month. The amount of atmospheric carbon dioxide is higher than at any time in the last 8,000. The trend toward runaway global warming (well beyond 2 degrees) is accelerating. And the action we are going to take to address the problem is about to make matters worse according to a new paper in the journal Nature.
We have tended to focus on our attention on greenhouse gases like carbon dioxide, methane and water vapour, which trap sunlight and warm the planet. However, climate scientists have always understood that there are other gases – like the sulphur dioxide produced when coal is burned – that have a ‘global dimming’ effect. Heavier aerosol and particulate materials such as those emitted by diesel and petrol engines also serve to reflect sunlight back into space, helping to cool the Earth’s surface. Without the cooling effect of these materials in the upper atmosphere, the greenhouse effect would have been greater, and climate change would have happened more rapidly:
“We find that surface radiation trends, which have been largely explained by changes in atmospheric aerosol loading, caused a cooling that masked approximately one-third of the continental warming due to increasing greenhouse gas concentrations over the past half-century.”
Our fossil carbon emissions have, in effect, provided us with a sun shade umbrella that has prevented us from getting sunburn; and we need to keep burning fossil carbon to maintain this cooling effect. But to lower global temperatures in the longer term, we are going to have to put the umbrella away… and that means that a lot of us are going to feel the heat in the immediate future.