James Hansen is at it again. Hansen, who runs NASA’s Goddard Institute for Space Studies in Manhattan, is usually billed as a climate scientist – not to mention the godfather of the current global warming concern.

But Hansen knows spends as much time marching in demonstrations and petitioning governments for action on climate change as he does doing research. He engages in plenty of unscientific rhetoric, such as calling trains taking coal to electrical generating stations “death trains” because of the carbon dioxide given off by burning coal to generate power. He has even testified in court in Britain on behalf of environmentalist vandals who sought to infiltrate a power plant and cause it to shut down.

Hansen and two other authors published a study this week that claims extreme weather events, especially droughts, are increasing in frequency and intensity and that it is “99% certain” that the cause is manmade global warming.

Nice conclusion – if your intent is to scare the public and politicians into action. But even many scientists not known as global warming sceptics have shaken their heads in disbelief at the sloppiness of Hansen’s latest work.

Hansen and his co-authors contend that the chances of having a drought such as the one that has gripped much of the continental U.S. this summer was just one in 300 in the years between 1950 and the 1980s, but the chance now is one in 10. This change, Hansen insists, can only be due to the negative effect human carbon emissions are having on climate.

But to arrive at their conclusions, Hansen and his colleagues had to “cherry-pick.” They had to carefully select the past years they compared to today. The period from the 1950s to the 1980s are well known for being substantially cooler than today. It makes the contrast look much more dire when you take a reasonably warm period such as the past 15 years and compare it to a notably cool period.

It may well be that droughts are much more common now than they were during the ‘50s, ‘60s, ‘70s and ‘80s. But that doesn’t tell us much about why.

For instance, as much or more of the globe was under drought conditions in the 1930s as it is today. But if Hansen et al admitted that, they might also have had to admit there are possible causes other than manmade emissions.

Much of the world was even warmer in the 1930s, but the cause couldn’t possibly have been idling SUVs and belching coal-fired power plants. To add the ’30s into the mix raises the possibility that other causes are at work or that, perhaps, extreme weather events are cyclical – recurring over time according to natural rhythms.

Martin Hoerling, a climate researcher with the National Oceanic and Atmospheric Administration who specializes in extreme weather, told the New York Times he felt Hansen was making too much of the certainty of the connection between possible climate change and drought.

Hoerling, who explains that he is also concerned about unnatural climate change, has published papers explaining that the devastating Russian heat wave of two summers ago was a naturally occurring weather event. The Times reports he has another study coming soon showing that natural factors are also behind the current American drought.

Hoerling insists Hansen confuses drought (which is a lack of rainfall), with heat waves. “This isn’t a serious science paper,” he told the Times. “It’s mainly about perception … (and) perception is not a science.”

Don’t take my word for it. I’m as biased on the sceptic side as Hansen is on the alarmist side. But you can believe Hoerling.