Russia's heat wave, drought and wildfires, by themselves, are not signs of global warming

"I don't think [Russian scientists] got it quite right," said climatologist Kevin Trenberth of the National Center for Atmospheric Research in Boulder, Colo. "I believe the correct interpretation is that nowadays everything has a component of natural variability and also global warming." The difference comes up often when global warming’s proponents — or detractors — try to base an argument one way or the other on a single event. "We can't say for sure that each event was due to human-caused climate change," said climatologist Michael Mann of Pennsylvania State University. "But the fact that the events are occurring more often, we can attribute to human-caused climate change.”