Ice sheets tell a scary new story

TheStar.com, Jul 14, 2007 04:30 AM

Cameron Smith

There was a thunderously important comment that went largely unnoticed in the reports published last spring by the United Nations Intergovernmental Panel on Climate Change (IPCC).

The comment noted there was a possibility polar ice sheets might be more vulnerable than predicted, because climate computer models didn't take into account recent observations. But there was no consensus on the significance of the shortcoming, the IPCC said.

Now, a team led by James Hansen, head of NASA's climate agency, has published a study that identifies what's going on at the poles, and confirms the vulnerability of the ice sheets. Its findings throw into question all the conclusions reached by the IPCC.

In particular, the study says ocean levels could rise by metres this century, not centimetres as the UN panel suggested. Worse still, what's occurring in polar ice fields could flip the world into much faster and far more devastating global warming than predicted by the IPCC.

This kind of fast transition has happened in the past – many times, according to paleoclimatic records, the Hansen study says – and it can happen now.

If it does occur, the study warns, it could produce runaway global warming powerful enough to raise sea levels 25 metres, as happened about 3.4 million years ago.

The study directly contradicts the IPCC, which expected the Antarctic ice sheet to get bigger, "due to increased snowfall." Instead, ice fields in West Antarctica could collapse if current trends are not reversed, the study says.

Hansen and his team looked at records of the past 450,000 years contained in ice cores and ocean sediment. They concluded melting ice caps can flip global warming suddenly into a runaway mode "out of humanity's control" and this would create "an inevitable and devastating sea-level rise."

What causes a flip is spiralling interactions. As warming from greenhouse gases increases, ice surfaces melt, and as they do they absorb more heat, because surface water reflects less of the sun's radiation than does snow and ice.

This causes surfaces to melt more quickly and broadly; melt tunnels carry water to the underside of glaciers where it acts as a lubricant speeding them to the sea; the ice sheet thins, lowering its surface in critical coastal areas; warming sea water loosens frozen underpinnings of ice fields; "icequakes" (lurching of ice sheets) increase; fractures and break-offs multiply; more ocean water is exposed to absorb heat.

The study calls this a non-linear response to global warming. The IPCC computer models were faulty, it says, because they assumed the response of ice fields would be linear. "(The IPCC) models are missing realistic, if any, representation of the physics of ice streams and icequakes ..." the study adds.

The world "may just have a chance" of avoiding a flip into disastrous climate change, it concludes. But only by holding global temperature increases to no more than 1 degree Celsius, and atmospheric concentration of carbon dioxide (CO2) to 450 parts per million. Missing these targets means straying into dangerous territory, it adds.

But half a degree of warming is inevitable because of gases already in the atmosphere, and CO2 concentration already is 384 ppm and is increasing by 2 ppm a year. Ten more years of a 2 ppm increase would make it "implausible" that the world could meet the target and get off the path to disaster, the study says.

It's a dire warning. I hope Canadians are paying attention.