Two degree limit: a dangerous way to think about climate change?

Photo by Flickr user Eladesor

The idea that any warming up to two degrees is ‘safe’ has shaped not just discussions on climate change, but the process of international negotiations. The Campaign against Climate Change has always tried to be clear that significant harm will take place well before this, and that we must consider the risk of triggering positive feedbacks such as the release of methane from Arctic melt.

How not to save the planet

The world is on the verge of passing 400ppm (parts per million) CO2.

As a reminder, pre-industrial levels were somewhere around 280ppm. A 'safe limit' might be 350ppm (yes, that's where got their name). As CO2 levels peak, as they do around May, each year, levels of 399.72ppm have already been recorded and 400ppm is likely in the next few days.

This news is breaking while countries gather in Bonn this week for yet more climate negotiations. We might expect to see Ministers and Prime Ministers rushing to respond to the crisis while the world's media holds its breath. Or not. In the words of anonymous blogger at the talks 'Low Carbonara' "The sense of urgency was palpable but only when it was time for lunch."

Photo by Sébastien Duyck of Adopt a Negotiator.

The two graphs below from the Scripps Institution of Oceanography show CO2 levels over the past 300 years and the past 800,000 years. It is clear that this concentration of CO2 is unprecedented for hundreds of thousands of years. In fact, the last time scientists estimate CO2 levels were around 400ppm were in the Pliocene, 5 million to 3 million years ago. Global temperatures were 3-4C higher than today, sea levels 5-40m higher. The difference is that today, levels of CO2 have risen over a few years, not millennia, and the rise shows no signs of stopping.