With cracks and holes in the Greenland ice sheet, we may well have to 'geo-engineer' the climate

In the Toronto Globe and Mail, Thomas Homer-Dixon adapts his chapter from an upcoming book, Globally Integrated Climate Policy for Canada (and I’ve shortened it considerably here – this is just a taste of Homer-Dixon’s essay): Next week, policy makers, scientists and activists from around the world will gather in Bali, Indonesia, to try to produce a climate-change agreement that will take us beyond the 2012 expiration of the Kyoto Accord. This meeting will take place in an atmosphere of sharply heightened unease among leading climate scientists.

A few years ago, these scientists regarded global warming as a matter of serious concern; now many appear to think that it's a matter of grave urgency — that we may be running out of time. The recent Intergovernmental Panel on Climate Change (IPCC) reports are increasingly viewed as out of date.

…Two issues particularly exercise climate scientists: positive feedbacks and ice-sheet dynamics.… Our climate has many positive and negative feedbacks. The positive ones are self-reinforcing, while the negative ones counteract the warming tendency. The big question for climate scientists then is: What is the balance is between the positive and negative feedbacks? A consensus appears to have emerged over the past two years — not yet reflected in the recent IPCC reports — that the positive feedbacks are much stronger and more numerous than the negative ones.

The second issue that particularly concerns climate scientists is ice-sheet dynamics… Climate scientists now recognize that the ice-sheet melting models in the IPCC reports were radically inadequate. These models were "static"; they assumed that atmospheric warming melts the ice, and the resulting water then runs off the surface of the ice sheet into the ocean.

…In light of these two trends, climate scientists are now beginning to discuss a topic that only two years ago many fervently hoped they'd never have to discuss: geoengineering, or the intentional human modification of the planet's climate to arrest or slow global warming. Geoengineering would involve, for example, putting sulphate aerosols into the atmosphere or putting mirrors into space to try to block a fraction of incoming solar radiation.

Today the topic is at the margins of the public-policy dialogue about climate change, but I expect it will be at the centre of public discussion within five years. In 10 years, we will see demands from some segments of the public and many opinion leaders that we carry out geoengineering. And we'll probably start doing it within 20 years, likely when it becomes apparent that the Greenland ice sheet is starting to collapse.

We will do it, because by then we'll be experiencing major socio-economic impacts of climate change — for instance, shortfalls in global food supply, as droughts and heat waves affect grain-growing regions. At that point, we will wonder about what kind of world we've created for our children and grandchildren. We'll recognize that we're facing an emergency unlike anything humankind has ever faced before, and we will demand that our leaders and experts do something, anything, to stop the slide.