The snow paralyzing America's east coast and falling on Jerusalem is an awkward backdrop to a new report that the record heat recorded in recent years is man's fault after all. Following reports that 2015 was the hottest year ever measured, after reports that 2014 had been, there is no more room for climate deniers to claim that the "science is not clear". It is.
Let's put it this way. If science says you have a 1 in 170,000 probability of winning the lottery if you pick Door No. 1, and the opposite if you pick Door No. 2, which door do you pick? Even if you're diehard GOP?
Nobody is arguing that the temperature measurements are wrong. A full13 of the 15 warmest years ever measured – ever measured! since measurement began! – were in this century. Yes, since 2000.
What has changed in that time? Not the environment in outer space where earth floats, nor has the sun indulged in unusual activity in that time. What has changed is the composition of Earth's atmosphere.
"Without greenhouse-gas emissions from burning coal and oil, the odds are vanishingly small that 13 out of the 15 warmest years ever measured would all have happened in the current, still young century," says the international scientific team in a paper coldly titled, "The Likelihood of Recent Record Warmth."
How vanishingly small? See the above example of the doors, and this.
Some media reports place the odds that the observed run of global temperature records would be expected to occur in the absence of human-caused global warming, as low as one in 650 million, or 1 in 27 million. Nonsense, say the scientists, taking a swipe at sensational journalism – but the odds they present are also terrifying.
The odds that that the sequence of record warm years would happen without human-caused global warming are between 1 in 5,000 and 1 in 170,000, they calculate – and that's based on 2014 data. Plug in the year 2015 and the odds are even slimmer.
Meaning, the odds that humans caused this are even higher. "2015 is again the warmest year on record, and this can hardly be by chance," stated co-author Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research.
The calculations are based on statistical analysis that combines observational data and computer simulations of the climate, to better distinguish between natural climate variability from human-caused climate change.
Many arguments have been made that the vagaries the planet has been suffering are weather fluctuations, not climate change. A key rebuttal against that claim is that the concentration of the greenhouse gas carbon dioxide has risen faster in the last 200 years (the period of the industrial revolution) that in the entire planetary history. Much faster.
"Natural climate variability causes temperatures to wax and wane over a period of several years, rather than varying erratically from one year to the next," elaborates the lead author Michael Mann, professor of meteorology at Penn State. "That makes it more challenging to accurately assess the chance likelihood of temperature records."
Given the recent press interest, Mann stated – and we add, the future of life - it "just seemed like it was important to do this right, and address, in a defensible way, the interesting and worthwhile question of how unlikely it is that the recent run of record temperatures might have arisen by chance alone."
In short, natural climate variations simply cannot explain the observed recent global heat records, spells out Rahmstorf. "But man-made global warming can."
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