The last three decades have been the warmest since scientists started keeping records in 1850, the Intergovernmental Panel on Climate Change (IPCC) has found. Releasing the fifth assessment report of its working group that deals with the physical science of climate change, the IPCC said global warming is unequivocal, definitely due to human activities and will raise the earth’s average temperature by more than 1.5C even if the activities that cause it are drastically reduced.
The warming is caused by the emission of greenhouse gases (GHG), mainly carbon dioxide. In the last 15 years, the warming has not been as high as predicted, which led to questions about climate science. Thomas Stocker, co-chair of IPCC’s Working Group I – the group that deals with the physical science – said this was because the oceans, especially their deep layers, had absorbed much of the extra heat, as much as 93%, according to some estimates.
But that is no reason for complacency, the scientists warned. When the IPCC released its last assessment report in 2007, it had said, “Climate change is the greatest challenge of our times.” Reiterating that, Stocker said at the release of the report in Stockholm on Thursday, “climate change is affecting the atmosphere, the oceans, the ice and the land.”
Climate change is already affecting farming worldwide, causing more frequent and more powerful storms, floods and droughts, and raising the sea level. The scientists have now worked out four GHG emissions scenarios, and found that at least a 1.5C increase in the earth’s average temperature (compared to 1850) would occur by 2100 under all four scenarios.
At global negotiations under the United Nations Framework Convention on Climate Change (UNFCCC), governments have resolved to keep this warming within 2C. Stocker pointed out that the world could not emit over 1,000 billion tonnes of carbon in order to stay within this limit, and 54% of that had been emitted already.
Michel Jarraud, head of the World Meteorological Organization, said, “To stay in the lower of the four scenarios, we have to take action now.” It was not just a question of higher temperature, he pointed out. “One of the biggest impacts of climate change is on the water cycle.”
The 831 authors and reviewers from 39 countries who have contributed to this Working Group I report have also concluded that under the lowest GHG emission scenario, the average sea level rise will still be 24 cm by 2050 and 40 cm by 2100. Under the worst of the four scenarios, the seas will rise by an average of 43 cm by 2050 and 63 cm by 2100. That puts a very large number of coastal communities at risk around the world.
Despite the earlier warnings of IPCC, the world is now on a path that will not keep global warming below 2C. Rajendra Kumar Pachauri, the chairperson of IPCC, said he would underline the message of the scientists at the next UNFCCC summit, scheduled in Warsaw this November.
Dahe Qin of the China Meteorological Administration, co-chair of the working group, said the report had special significance for developing countries, because many of them were especially vulnerable to the effects of climate change. Plus, the lifestyle choices they made on their road to development would determine climate change scenarios in a big way. “If every Chinese family has three to four cars as in America, it will be a catastrophe for China and the world,” he said.
has two more working groups – one to look at the impacts of climate change and one to look at ways to reduce GHG emissions. Their reports are scheduled next year.