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Some 15,000 years ago, the spot where I am now writing this – Hampshire in England – was uninhabitable. The Arctic tundra that came before the green fields was home to very few animals and no humans. The ice sheet stopped only a few miles north of here, hardly moving for tens of thousands of years. Today’s great cities including Birmingham, Manchester and Edinburgh were all under a kilometre of ice. Such a contrast to today only 15,000 years later. When the ice receded, the trees took over. It has been said that you would have been able to travel from the most southern to the furthest northern point of ancient Britain without touching the ground.

That the trees no longer completely canopy this land is due to mankind as we cleared the forests. That the ice is no longer here is due to global warming. Without doubt, we live in an interglacial period – a warm time between ice ages. There have been many during the current great glaciation. Some have these periods have been warmer than today, many shorter than our current interglacial’s duration. The return of the ice would, short of a giant meteor strike, be the biggest disaster to face humanity. Vast swathes of the northern Hemisphere would be frozen. Northern Europe, Asia, Canada and the United States would have extensive regions rendered uninhabitable. Mankind would have to move south. There would be no choice as no technology could stop the ice or allow our high populations to life amongst it. Some believe the return of the ice will not happen for thousands of years, other that the signs could be visible within decades.

But could it be that the greenhouse gasses being pumped into the atmosphere, that many believe are responsible for a recent warming of the planet, might counteract the forces bringing us a new glaciation? Could it be that greenhouse gasses might actually stave off the return of the ice and save the lives of tens of millions, if not civilisation itself? A recent study by scientists at Cambridge University and published in the Journal Nature Geoscience suggests that the carbon dioxide might extend the current interglacial until carbon dioxide levels fall. They believe that the atmospheric concentration of CO2 must be about 240 parts per million before glaciation could start.

Currently, it is about 390 ppm. In a 1999 essay, Sir Fred Hoyle said: “The renewal of ice-age conditions would render a large fraction of the world’s major food-growing areas inoperable and so would inevitably lead to the extinction of most of the present human population. We must look to a sustained greenhouse effect to maintain the present advantageous world climate. This implies the ability to inject effective greenhouse gases into the atmosphere, the opposite of what environmentalists are erroneously advocating.”

We do not know the precise causes of ice ages or of the timing of interglacials. The earth’s orbit about the sun is one factor, but there seem to be others and no scientist has anything other than a partial explanation. It may be that the Cambridge scientists are correct, though they believe the CO2 in our atmosphere has gone way beyond levels needed to delay the ice’s return. It may be, in the complex interplay of climatic parameters, that high CO2 might hasten the return of the ice sheets. There is some evidence that during some harsh glaciations over 400 million years ago, the CO2 level was more than ten times today’s amount. There is much uncertainty here, but also an intriguing question. Do we want to reduce CO2 in our atmosphere to pre-industrial levels? Or would we all be better of maintaining a higher level? Or perhaps, nature might surprise us yet again.

Public Service Europe, 11 January 2012