Humankind responsible for global warming, says IPCC
'This day marks the removal from the debate over whether human action has anything to do with climate change,' said Achim Steiner, Director of the United Nations' Environment Programme, as the latest report by the Intergovernmental Panel on Climate Change (IPCC) was released.
The report not only pins the blame for climate change on humankind, but states with new certainty what further changes the globe should expect to witness over the coming decades.
Policy-makers have asked for scientific proof, and that proof is now on the table, said Dr Steiner. He appealed for the launch of the report to be remembered at the moment that marks a shift from doubting to action, and claimed that anyone who still delays 'will be considered as irresponsible in history books'.
The IPCC's main findings were presented by Susan Solomon of the National Oceanic and Atmospheric Administration in the US. 'Warming in the climate is now unequivocal,' she said. Paleoclimatic work has shown that the last half century has been 'unusually warm', and that the last time the polar regions were significantly warmer than they are now was 125,000 years ago and due to a change in the Earth's rotation.
Perhaps the biggest change since the last IPCC report in 2001 is the certainty with which scientists can now say that human beings are implicated in climate change. In 2001 it was 'likely' that human activities were to blame, meaning a probability of between 66% and 90%. Now, in 2007, the IPCC says that it is 'very likely' that humans are to blame, meaning the probability has increased to 90%.
If emissions are kept at a constant, at today's levels, the planet is expected to heat up by 0.2°C every decade. Even if emissions are reduced, warming is likely to continue due to the aerosols that are already in the atmosphere. This phenomenon is known as 'committed warming'.
If emissions continue to rise, the planet will see even more changes during the 21st century than were evident in the 20th century, Professor Solomon warned.
The report predicts that temperatures will rise by between 1.8°C and 4°C, but suggests that they could rise by as much as 6.4°C. Report co-author Michael Manning suggested that a world with temperatures of 6.4°C warmer than now would have an ice-free Arctic, more extreme and frequent heatwaves, and more tropical cyclones. 'We'd see what we've seen through the second half of the 20th century, but everything would be much more severe,' he said.
The IPCC's findings have been summarised in a document for policy-makers. 'We are looking for unequivocal commitment from policy-makers, business leaders and civil society,' said Dr Steiner.
Dr Solomon was less willing to get involved in dictating which policy approaches should now be taken, or how urgently action is needed. 'Science can best serve society by not going beyond its expertise. There are people out there who have this role [...]. The report is not policy-prescriptive, but policy-relevant, and I think that's how it should be,' said Dr Solomon.
The report 'Climate Change 2007: The Physical Science Basis' was written by some 600 scientists from 40 countries. Over 620 expert reviewers and a large number of government reviewers also participated.
The full report will be released later in the year, along with other IPCC chapters on the probably impacts of climate change, options for adapting to these impacts, and possible routes to reducing the emission of greenhouse gases.
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