The consequences of a global temperature rise of 4C are catastrophic: from drought, to heatwaves, to crop failure and disease. Photograph: Reuters
As environment web editor, I think a lot about the risk of doom-mongering we run when reporting gloomy environmental news. But risk is in fact what this is all about: how lucky do we feel in gambling with the planet's future?
In our exclusive today, Bob Watson, one of the world's most eminent climate scientists, says that while we should aim to limit the rise in global temperature to 2C, we must prepare for a rise of 4C. That 4C is a global average, by the way, and higher latitudes will see higher rises. The reason we must hope for the best and prepare for the worst is that there is a chance that the worst will occur, and that chance is not insignificant.
Sir David King, the UK government's former chief scientific adviser, who supported Watson's warning, notes that even with a comprehensive global deal to keep carbon dioxide levels in the atmosphere at below 450 parts per million there is a 50% probability that temperatures would exceed 2C and a 20% probability they would exceed 3.5C.
The list of consequences of such large rises in temperature over the next century are simply catastrophic, from drought, to heatwaves, to crop failure and disease. The journal Nature has published excellent summaries of the global impacts and regional impacts.
But as scary - and familiar - as such points are, a couple of other things stood out to me. First, Watson says: "We don't know in detail how to limit greenhouse gas emissions to realise a 2C target." Now this man battled the ozone hole, chaired the IPCC, advised the Clinton administration, was chief scientist at the World Bank and is now science adviser to the UK government's environment department. If he doesn't know, no one does.
Perhaps even more terrifying is the reaction of Neil Adger, an expert on adaptation to climate change at the Tyndall Centre for Climate Change Research in Norwich, UK:
Thinking through the implications of four degrees of warming shows that the impacts are so significant that the only real adaptation strategy is to avoid that at all cost because of the pain and suffering that is going to cost. There is no science on how we are going to adapt to 4C warming.
So the risks are both huge and real. The only thing that stops a full-blown panic is the timescale. These impacts will strike over decades, though they are being set in train now. The big question then is how can urgent action be stimulated in governments, business and individuals to tackle this clear and future danger? All ideas welcome.
