A major new study has reanalyzed the connection between global warming and the record-breaking temperatures we’ve been seeing. Stefan Rahmstorf and Dim Coumou conclude in their PNAS paper, “Increase of extreme events in a warming world“:
… the majority of monthly records like the Moscow heat wave must be considered due to the warming trend. In highly aggregated data with small variability compared to the trend, like the global-mean temperature, almost all recent records are due to climate warming.
Basically, they show that when there is a lot of variability in temperature, as there is on in individual days, finding a trend in extreme records at any single location thanks to global warming is small: “daily data from a single weather station may not yet show a major change in temperature extremes due to global warming.”
But when you look at the monthly and especially yearly temperature data at a location, data that have considerable less fluctuation, then a warming trend is far more likely to create a new record. And as lead author Rahmstorf explained to me, this matters because “monthly temperature records have much more impact on human society” in terms of impact on human health, mortality, and crop failures.
And, of course, the Russia’s heat wave apparently caused very high mortality. As Reuters reported last year, “Nearly 56,000 more people died nationwide this summer than in the same period last year, said a monthly Economic Development Ministry report on Russia’s economy.” And it caused Russia to ban grain exports for over a year after their crops shriveled (see Russian President Medvedev: “What is happening now in our central regions is evidence of this global climate change, because we have never in our history faced such weather conditions in the past”).
The PNAS study found:
For July temperature in Moscow, we estimate that the local warming trend has increased the number of records expected in the past decade fivefold, which implies an approximate 80% probability that the 2010 July heat record would not have occurred without climate warming.
Global warming increased the chance of this monster heat-wave occurring by a factor of 5. I’d note that Tamino doing a far cruder analysis had estimated global warming had increased its chances by a factor of 8.
This is only a bombshell because NOAA did a flawed analysis just a few months ago that found no connection between global warming and the record-smashing. Back in March, NCAR Senior Scientist Kevin Trenberth challenged NOAA’s attribution analysis, “Many statements are not justified and are actually irresponsible,” as Climate Progress reported. It is unusual for a major study like that to be essentially refuted in such a short time in the peer-reviewed literature.
Rahmstorf told Wired that the NOAA study showed “an absence of evidence, not evidence of absence. We found the evidence.” Here is one key figure: