'Climate change is more certain than ever'

Climate change is one of the defining issues of our time and the indisputable warming of the world over the past century is largely the result of human activities, according to the two most august science bodies in Britain and the United States.

The speed of global warming is now 10 times faster than at the end of the last ice age, which represents the most rapid period of sustained temperature change on a global scale in history - and there is no end in sight if carbon emissions continue to increase, the Royal Society and the US National Academy of Sciences have warned.

Concentrations of carbon dioxide in the atmosphere are the highest for at least 800,000 years and 40 percent higher than they were in the 19th century. They are set to increase even further without a binding global agreement on significant cuts in industrial emissions, the scientists said. Average global surface temperatures have increased by 0.8C since 1900 and the past 30 years have been the warmest in 800 years. On the current carbon dioxide trajectory, global warming could increase further by between 2.6C and 4.8C by 2100, which would be about as big as the temperature difference between now and the last ice age, they said.

"Detailed analyses have shown that the warming during this period is mainly the result of the increased concentrations of CO2 and other greenhouse gases. Continued emissions of these gases will cause further climate changes in regional climate," says a joint report by the two academies.

In a foreword to "Climate Change Evidence and Causes", Ralph Cicerone, president of the National Academy of Sciences, and Sir Paul Nurse, president of the Royal Society, say that climate change is now more certain than ever and that many lines of evidence point to human activity as the cause.

"The evidence is clear. However, due to the nature of science, not every single detail is ever totally settled or completely certain. Nor has every pertinent question yet been answered," the two presidents say.

"Some areas of active debate and ongoing research include the link between ocean heat content and the rate of warming, estimates of how much warming to expect in the future, and the connections between climate change and extreme weather events," they say.

The aim of the joint report, written as a series of answers to 20 questions, is to make a clear statement to policy makers and the wider public about the scientific basis of climate change and its uncertainties, which should not distract from the main message about what needs to be done, said Prof Tim Palmer of Oxford University, one of the report's main authors.

"Every day we are putting more CO2 into the atmosphere and for all practical purposes once we put it there it is there forever. So we can wait 10 or 20 years to get a better estimate of the science but of course in that time you'll have 20 years of CO2 emissions that are going to be impossible to reverse," Prof Palmer said.

"We are talking about changes where there will be a distinct risk by the next century of something that could in terms of global temperatures be as big as that between today and the last ice age. Do we want to take that risk?" he asked.

"Every day we do nothing is another load of carbon in the atmosphere that we'll never get rid of in many generations and it's effectively there forever.

We are not trying to promote policy or be endorsers of government policy, we're just trying to give our best estimates of the science," he said.

The report says there is no "pause" in global warming only a temporary and short-term slowdown in the rate of increase in average global surface temperatures in the non-polar regions which is likely to start accelerating again in the near future. "Globally averaged surface temperature has slowed down. I wouldn't say it's paused. It depends on the datasets you look at. If you look at datasets that include the Arctic, it is clear that global temperatures are still increasing," Prof Palmer said.

- The Independent