JOHN MAYNARD Keynes famously replied to criticism during the Great Depression that he had changed his position on monetary policy, by saying: “When the facts change, I change my opinions. What do you do, sir?”. The conversion of Richard Muller, professor of physics at the University of California in Berkeley, from being a self-proclaimed sceptic on climate change to someone who now believes that global warming is real and that “humans are almost entirely the cause” has been widely reported. Referring to the latest findings of his Berkeley Earth Surface Temperature project, he even echoed Keynes by saying: “We were not expecting this, but as scientists it is our duty to let the evidence change our minds.”
Although Muller’s claim to be a converted sceptic has been challenged by others, the data accumulated by his team of scientists is certainly impressive – merging more than 14 million land temperature observations from 44,455 sites dating back to 1753; previous data sets only went back to the mid-19th century and used a fifth as many records. What the data showed was that the Earth’s land surface had warmed by 1.5 degrees Celsius over the past 260 years. “Moreover, it appears likely that essentially all of this increase results from the human emission of greenhouse gases”, Muller wrote recently in the New York Times. “I expect the rate of warming to proceed at a steady pace, about one and a half degrees over land in the next 50 years.”
In his article, Muller said it’s a scientist’s duty to be “properly sceptical” and he still finds that “much, if not most, of what is attributed to climate change is speculative, exaggerated or just plain wrong”. Quite separately from the Berkeley Earth Surface Temperature project, he said he had “analysed some of the most alarmist claims, and my scepticism about them hasn’t changed”. For example, he believes that Hurricane Katrina “cannot be attributed to global warming”, noting that the number of hurricanes hitting the US “has been going down, not up; likewise for intense tornadoes”. But Muller is almost certainly wrong in saying that the recent heatwave in the US “happens to be more than offset by cooling elsewhere in the world, so its link to global warming is weaker than tenuous”.
For the past 25 years, scientists have been warning that extreme weather events – both hot and cold – would be part of the pattern of our changing climate. It’s also likely that 2012 will end up being yet another record year for average global surface temperatures.