Scientists call on leaders to "act now" to avert climate catastrophe

Climate scientists yesterday issued an unequivocal warning to political and business leaders that they must act now to cut carbon emissions or risk "abrupt or irreversible climatic shifts" that would have a devastating impact on global society.

In a break with the scientific convention of refusing to comment on policy issues, the meeting of more than 2,500 climate scientists in Copenhagen closed with the release of a statement warning that there was "no excuse for inaction".

It went on to urge world leaders to build on "a growing public desire for governments to act on climate change," while removing "implicit and explicit subsidies" and "reducing the influence of vested interests that increase emissions and reduce resilience". It also called for "an effective, well-funded adaptation safety net" for those least capable to cope with the already inevitable impacts of climate change.

The statement was presented to Danish prime minister Anders Fogh Rasmussen, who will host the forthcoming UN-backed climate change talks to be held in Copenhagen.

It will be followed in June by a full synthesis of the numerous reports presented at this week's conference, which together confirmed that the pace and impact of climate change is currently in line with the very worst-case scenarios set out by the Intergovernmental Panel on Climate Change that has to date underpinned the UN negotiations.

Yesterday's summary of the evidence warned: "The climate system is already moving beyond the patterns of natural variability within which our society and economy have developed and thrived. These parameters include global mean surface temperature, sea level rise, ocean and ice sheets dynamics, ocean acidification, and extreme climatic events. There is a significant risk that many trends will accelerate, leading to an increasing risk of abrupt or irreversible climatic shifts."

Professor Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research said that many of the key indicators of climatic change were now " going faster and worse than expected", adding that historical records showed that climatic changes were both "abrupt and "unstable".

Many scientists at the event warned it was now highly unlikely that the EU's target of limiting temperature rise to two degrees above pre-industrial levels could be met, adding that based on current trends, there was a risk of catastrophic temperature rises of five to six degrees by the end of the century.

They warned that based on current trends, there was a high level of risk that the end of the century would be characterised by sea level rises of one metre or more; the collapse of rainforest and marine ecosystems; the desertification of much of southern Europe; disruption to the monsoon system that supports more than one billion people; and the collapse of global "carrying capacity", the population the world can support, to just one billion people.

Speaking at the closing of the conference, Lord Nicholas Stern, author of the Stern Review on the costs of climate change, said that it was now clear that "inaction was inexcusable".

He reiterated that it would cost just one to two per cent of GDP over the next few decades to stabilise atmospheric concentrations of greenhouse gases at 500 parts per million of CO2 equivalent before reducing them to lower levels. " We should see action as rather attractive and inaction as inexcusable," he said. "High carbon growth kills itself, first through higher prices for hydrocarbons, then through the climate crisis it creates."

Stern also argued that the recession represented an ideal opportunity to invest in low-carbon technologies and business models. "Resources over the next two to three years will be cheaper than they will be in the future," he said. " Now is the time to get the unemployed of Europe working on energy efficiency."