The hockey-stick curve

The problem of and solutions to climate change. The imperatives of transition on the eve of the Bali meet

There has been a rapid increase of co₂ concentrations in the atmosphere over the past 250 years: from 280 parts per million (ppm) to 379 ppm. All greenhouse gases add up to the equivalent of 430 ppm of co₂. That this increase has had a warming effect because of heat energy trapped in the atmosphere is clear when one compares the well known hockey-stick graph of emissions with corresponding global temperature change.

There is a direct correlation between co₂ build-up and temperature increase. The Earth has warmed by 0.7c since around 1900; 11 of the last 12 years (1995-2006) have been the warmest since temperatures were measured (1850). The world saw nearly stable temperatures for around 1,000 years and then a sharp increase since 1800.

The fact that climate change is real, that it is happening and that its impacts are devastating millions is no longer news. In its fourth synthesis report, the Intergovernmental Panel on Climate Change ( ipcc) has told us that the "warming of the climate system is unequivocal as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level". Clearly, the science of climate change has to be accepted even if its politics is still contested.

The only question that remains open is whether current science is underestimating the urgency and impact of climate change. ipcc is seen as conservative and cautious. Because of the time lag between its reports, it is feared that what we know today may already be out of date. Its current assessment does not take into account dramatic recent evidence, including the shrinking of the Arctic ice cap, news that Greenland is losing its mass faster than anticipated, a surge in atmospheric concentration of co₂ and an apparent slowing of the Earth's ability to absorb greenhouse gases.

Taken together, it could well be that the climate is reaching its 'tipping' point, which will further accelerate changes in the years to come.

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