BBC: Proposed Carbon Targets Above Historical Safety Levels
A new historical record of carbon dioxide levels suggests current political targets on climate may be “playing with fire”, scientists say.
Researchers used ocean sediments to plot CO2 levels back 20 million years.
Levels similar to those now commonly regarded as adequate to tackle climate change were associated with sea levels 25-40m (80-130 ft) higher than today.
What that level is has been the subject of intense debate down the years; but one figure currently receiving a lot of support is 450ppm.
On Tuesday, for example, the International Energy Agency (IEA) released its prescription for tackling climate change, which sees concentrations of greenhouse gases peaking at the equivalent of 510ppm of CO2 before stabilising at 450ppm.
The Boxer-Kerry Bill, which has just entered the US Senate, also cites the 450 figure.
“Trouble is, we don’t know where the critical CO2 or temperature threshold is beyond which ice sheet collapse is inevitable,” said Dr Overpeck.
“It could be below 450ppm, but it is more likely higher – not necessarily a lot higher – than 450ppm.
“But what this new work suggests is that… efforts to stabilise at 450ppm should avoid going up above that level prior to stabilisation – that is, some sort of ‘overshoot’ above 450ppm on the way to stabilisation could be playing with fire.”