Scientists blame humans for global warming

Unpublished
Stockholm - A landmark report says scientists are 95% certain that humans are the "dominant cause" of global warming since the 1950s. The report by the UN's climate panel details the physical evidence behind climate change. On the ground, in the air, in the oceans, global warming is "unequivocal", it explained. It adds that a pause in warming over the past 15 years is too short to reflect long-term trends. The panel warns that continued emissions of greenhouse gases will cause further warming and changes in all aspects of the climate system. To contain these changes will require "substantial and sustained reductions of greenhouse gas emissions". After a week of intense negotiations in the Swedish capital, the summary for policymakers on the physical science of global warming has finally been released. The first part of an IPCC trilogy, due over the next 12 months, this dense, 36-page document is considered the most comprehensive statement on our understanding of the mechanics of a warming planet. It states baldly that, since the 1950s, many of the observed changes in the climate system are "unprecedented over decades to millennia". Each of the last three decades has been successively warmer at the Earth's surface, and warmer than any period since 1850, and probably warmer than any time in the past 1,400 years. "Our assessment of the science finds that the atmosphere and ocean have warmed, the amount of snow and ice has diminished, the global mean sea level has risen and that concentrations of greenhouse gases have increased," said Qin Dahe, co-chair of IPCC working group one, who produced the report. Since 1950, the report's authors say, humanity is clearly responsible for more than half of the observed increase in temperatures. However, the report does alter a key figure from the 2007 study. The temperature range given for a doubling of CO2 in the atmosphere, called equilibrium climate sensitivity, was 2.0C to 4.5C in that report. In the latest document, the range has been changed to 1.5C to 4.5C. The scientists say this reflects improved understanding, better temperature records and new estimates for the factors driving up temperatures. In the summary for policymakers, the scientists say that sea level rise will proceed at a faster rate than we have experienced over the past 40 years. They say that ocean warming dominates the increase in energy stored in the climate system, accounting for 90% of energy accumulated between 1971 and 2010. For the future, the report says that projected warming for the end of this century is likely to exceed 1.5C, relative to to the period 1850-1900. (FA)

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