For many scientists and politicians a 2 degrees centigrade rise is the threshold which we cannot afford to cross. For example, the IPCC has long argued that climate impacts will significantly increase, if and when, global temperatures rise 2 degrees C or more above pre-industrial levels.

Based on the science, the EU’s stated political objective is to ensure that global average temperatures do not increase more than 2°C.

The dangers of going over 2 degrees are well-known. Anything over and it is predicted that we will suffer dangerous and irreversible effects. A 2 degree increase means some 200 million more people will be at risk of malaria and other vector diseases, up to 3 billion at risk of water shortages, and the complete and irreversible melting of the Greenland ice, with up to 50 million at risk of sea-level rise.

In short, the dangers of a two degrees rise seem potentially catastrophic.  However, most climate scientists now believe that temperatures will rise even further. Almost nine out of 10 climate scientists do not believe political efforts to restrict global warming to 2C will succeed, a poll found for the Guardian yesterday. The scientists believe an average temperature rise of 4-5C by the end of this century is more likely.

The magnitude of the changes this would bring is truly scary. It would disrupt food and water supplies, exterminate thousands of species of plants and animals and trigger massive sea level rises that would swamp the homes of hundreds of millions of people.

The Guardian asked leading climate scientists who attended last month’s climate conference in Copenhagen asked whether the 2C target could still be achieved, and whether they thought that it would be met: 60% of respondents argued that, in theory, it was still technically and economically possible to meet the target. However 39% said the 2C target was impossible.

Asked what temperature rise was most likely, 46% said it would reach 3-4C by the end of the century and 26% suggested a rise of 2-3C, while a handful said 6C or more.

Scary stuff.