Climate scientists warn of "devastating" five-degree world

Climate scientists gathering in Copenhagen today attempted to hammer home the full scale of the threat posed by global warming, warning that we are currently on track for a "five-degree world" where the global population would be slashed from an expected nine billion in 2050 to just one billion people by the end of the century.

Opening the final day of the Climate Congress meeting was Professor John Schellnuber of the Potsdam Institute for Climate Impact Research and one of the world's leading climate scientists. He said the evidence gathered since the UN-backed Intergovernmental Panel on Climate Change "closed the books" on its report four years ago confirmed the outlook was far more bleak than previously thought.

He said that he had recently updated German chancellor Angela Merkel on research that revealed that even if the world achieves the EU target of limiting warming to two degrees above pre-industrial levels, the climate impacts will be far more severe than previously thought.

He also warned that emissions were continuing to grow faster than anticipated, while carbon sinks such as tropical rainforests and oceans were becoming less effective at storing carbon, meaning that far deeper emission cuts would be required.

Schellnuber said that to even achieve a five out of six "Russian roulette" chance of limiting temperature rises to two degrees would require global emission cuts of 80 per cent by 2050, significantly higher than the 50 per cent target currently being discussed in the lead up to the UN-backed Copenhagen meeting in December.

"A 50 per cent cut does not even give us a Russian roulette chance," he warned.

Schellnuber said that the alternative to deep cuts in carbon emissions was a "five-degree world" that would activate a number of tipping points such as the collapse of the rainforest, the accelerated melting of the Greenland ice sheet, the disruption of the monsoon system, and the creation of "oxygen holes" within the seas that would have disastrous consequences for the food chain.

He warned that in such a world, global carrying capacity, the number of people the world can support, would stabilise at fewer than one billion people.

Lord Nicholas Stern, the author of the influential Stern Review, said that climate scientists had to be more vocal about the risk of " devastating" five-degree-plus levels of warming. He argued that the previous focus on what two or three degrees of warming would be like had contributed to flawed economic models in which the potential damage from climate change had been badly underestimated.

"You need to tell us clearly and strongly what five degrees would look like, " he said. "This means fundamentally radical changes of where people can live... hundreds of millions, even billions, of people would have to move and that would create huge conflict."

Schellnuber said that it was still possible to limit global warming to manageable levels, but a wide-reaching international deal would be required that would have to be capable of delivering a huge expansion of environmentally protected areas, the establishment of a global emissions trading scheme that would benefit poorer countries, and the launch of at least 12 climate change " Apollo Projects" such as the development of a Europe-wide super grid drawing on solar thermal plants in the Sahara.

In addition, he proposed a number of measures that are likely to face opposition from the developed world. He outlined plans for a global commons scheme that would guarantee developing countries a share of agriculturally productive land in Europe and the US in return for their commitment to protect globally significant forests, and a quota for accommodation of climate refugees. "If the US produces 25 per cent of emissions, it has to take 25 per cent of the refugees," he proposed.