The Road to Copenhagen - Numbers

We need some greenhouse gases such as CO₂ in the atmosphere, but the question is how much? Recent science shows that we are already way above the safe level. Global warming is already having an impact - as in the earlier than expected disappearance of the Arctic sea ice in summer.

For all of human history until about 200 years ago, our atmosphere contained 275 parts per million of carbon dioxide (CO₂). Parts per million (ppm) is simply a way of describing how much gas is there. Many climate scientists say 350 parts per million is the safe upper limit for CO₂ in our atmosphere.

Beginning in the 18th century, humans began to burn coal and gas and oil to produce energy and goods. The amount of carbon in the atmosphere began to rise, at first slowly and now more quickly. The planet now has 385 ppm CO₂ - and this number is rising by about 2 ppm every year. 385 ppm is higher than any time seen in the recorded history of our planet.

In December world leaders meet in Copenhagen to finalise a new global climate change agreement. Despite the recent science, policy-makers are still talking about stabilizing CO₂ at much higher levels than the safe 350 ppm threshold.

James Hansen of NASA wrote recently, 'If humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted, paleoclimate evidence and ongoing climate change suggest that CO₂ will need to be reduced from its current 385 ppm to at most 350 ppm.'

That will be a hard task, but it is technically possible. We know what we need to do. We need to stop taking carbon out of the ground and putting it into the air. By using solar, wind and other renewable energy, improving agricultural practices, climate friendly transport and halting deforestation we can get back to 350 ppm by mid-century.

Bill McKibben, an American Methodist, spearheads a campaign to raise awareness of this 350 ppm target. On October 24th many church bells around the world will peal 350 times to symbolize its importance. During the last war the nation's church bells were put on alert ready to peel to signal an invasion. The threat now is even greater - a global emergency is upon us and humanity must do whatever it takes to drive down CO₂ to a sustainable level for life as we know it on this beautiful earth.

Barbara Echlin and Ruth Jarman

Download an A5 doc version: Numbers

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