Trenberth: The answer to the oft-asked question of whether an event is caused by climate change is that it is the wrong question. All weather events are affected by climate change because the environment in which they occur is warmer and moister than it used to be….
The air is on average warmer and moister than it was prior to about 1970 and in turn has likely led to a 5–10 % effect on precipitation and storms that is greatly amplified in extremes. The warm moist air is readily advected onto land and caught up in weather systems as part of the hydrological cycle, where it contributes to more intense precipitation events that are widely observed to be occurring.
Seasonal Jun-Jul-Aug 2010 sea surface temperature (SST) anomalies relative to 1951–70. Record high SSTs were recorded in the locations and at the times indicated with record flooding nearby.
Like a baseball player on steroids, our climate system is breaking records at an unnatural pace. And like a baseball player on steroids, it’s the wrong question to ask whether a given home run is “caused” by steroids. Meteorologist Dr. Jeff Masters explained the analogy this way last December:
… we look at heat waves, droughts, and flooding events. They all tend to get increased when you have this extra energy in the atmosphere. I call it being on steroids kind of for the atmosphere….
Well, normally, you have the everyday ups and downs of the weather, but if you pack a little bit of extra punch in there, it’s like a baseball hitter who’s on steroids.
You expect to see a big home run total maybe from this slugger, but if you add a little bit of extra oomph to his swing by putting him on steroids, now we can have an unprecedented season, a 70 home run season. And that’s the way I look at this year.
We had an unprecedented weather year that I don’t think would have happened unless we had had an extra bit of energy in the atmosphere due to climate change and global warming.
I’m reposting all this because of a recent editorial in the journal Nature that seems to have missed the key point. Below is a response to that editorial by NASA’s Gavin Schmidt at RealClimate, followed by a comment on the editorial from Trenberth.
First, though, it’s worth noting in March that Nature Climate Change published a major new analysis of the scientific evidence, “A decade of weather extremes” (subs. req’d) — see my post Nature: Strong Evidence Manmade ‘Unprecedented Heat And Rainfall Extremes Are Here … Causing Intense Human Suffering’. That Nature analysis concluded:
It is very likely that several of the unprecedented extremes of the past decade would not have occurred without anthropogenic global warming.
Here is the RealClimate piece: