Rajendra Pachauri, head of the UN-backed Intergovernmental Panel on Climate Change, said data was still coming in about yesterday's deadly tornado which tore through a suburb of Oklahoma City.
"Could there be better preparedness in general? Yes. What could better preparedness have been? Well it's very difficult to say at this stage," Pachauri told reporters in Geneva.
"But one really cannot relate an event of this nature to human-induced climate change. It's just not possible. Scientifically, that's not valid," he said.
Tornadoes frequently touch down on Oklahoma's plains, but yesterday's twister struck a populated urban area.
Because of the hard ground, few homes are built with basements or storm shelters where residents can take cover.
Oklahoma City lies inside the so-called "Tornado Alley" stretching from South Dakota to central Texas, an area particularly vulnerable to tornadoes.
Experts warn that other extreme weather events -- like last year's Hurricane Sandy in the Caribbean and United States -- could strike more often due to climate change, as global temperatures rise and governments struggle to rein in emissions of greenhouse gases which are blamed for the phenomenon.
