It has begun.
As a powerful El Niño event, one that helped push the planet to some of its warmest temperatures on record, fades away, some voices are now heralding a new bout of sudden planetary cooling. It started last week with an article in The Mail on Sunday, and then rippled to a Breitbart article that itself received a tweet from the House Science Committee.
And if past debates over the planet’s temperature are any guide, this could just be the beginning.
The original Mail on Sunday article, by David Rose, asserted that “global average temperatures over land have plummeted by more than 1C since the middle of this year – their biggest and steepest fall on record.” The assertion, the article said, was based on measurements of the planet’s atmosphere by satellites – and moreover, measurements that were taken “over land,” thus excluding the planet’s oceans. Breitbart then said (in its headline) that this temperature “plunge” had been met by “icy silence from climate alarmists.” “The last three years may eventually come to be seen as the final death rattle of the global warming scare,” argued author James Delingpole.
Climate scientists, in turn, have been highly critical — a band of them just extensively challenged the original Mail on Sunday article at the website Climate Feedback, where they “estimated its overall scientific credibility to be ‘very low.’”
“This article is a textbook case of cherry picking—it selects only one record, ignores the limitations of the data it comments on, and forms an argument based on only a few months of a much longer record,” argue the researchers. Rose, however, argued back on Twitter that the critique “misrepresents what I wrote” and that “I never said long term trend not due to GHG!,” the acronym for greenhouse gases.
So what’s happening here?
The Mail on Sunday article chooses its words carefully, and Rose is right that he didn’t deny global warming outright — but the impact was pretty clearly to sow doubt, overall, about the causes behind the scorching temperature period we’ve just lived through.
Moreover, the selection of data remains problematic. Carl Mears, a physicist at Remote Sensing Systems, told the Post he thinks it is “very likely” that the Mail on Sunday article was using his own institution’s satellite temperature dataset. But Mears, who was not part of the Climate Feedback critique, also says he sees the reliance on land data, in particular, as “cherry picking.”
“The size of the temperature drop is increased because of a weather pattern which led to below normal temperatures over Siberia…and somewhat warmer temperatures elsewhere (including over the northern hemisphere oceans, which are not part of the land average),” Mears explained. “This is likely what led to it being a record temperature drop.”
In contrast to such a short-term temperature fluctuation over land, here is the overall surface temperature trend, including both the land and the oceans, since 1880, per NASA. It is not based on satellites, which provide a far shorter record and a problematic one in some ways. It does not yet include 2016, which is highly likely to be the hottest year of them all and would only make the figure more dramatic. But then, you don’t really need that to see what is going on:
There’s obviously no long term cooling trend here, and especially not since the 1970s. But the figure gives a hint as to how one can easily make claims about short term cooling bouts, like the ones cited above.
Check out the early 1940s and the years 1997-1998 above, two periods that see little global warming exclamation points. These are two particularly noteworthy El Niño periods. At the very end of the record, even though 2016 isn’t included, is the beginning of another.
As you can see, when these extra hot periods end, the ensuing months or even years can’t compete with them for temperatures. Yes, you could technically call this a cooling — or, if the transition is particularly sharp, temperatures “plummeting” – but by doing so you risk really missing the big picture about the trend pictured above. The big picture is that it’s warming, and when a large El Niño comes, it tends to set a major new temperature record, vanquishing not only all other years but all prior El Niños.
Granted, the Mail on Sunday article does correctly note that whatever cooling we’re seeing now is related to the end of El Niño. But the article also suggested that the 2016 warm temperature record may have been only El Niño related, rather than a reflection of global warming. Many scientists dispute that.
“The temperature before the 2015-2016 event was much warmer than the temperatures before the 97-98 event,” says Mears. “This means that the assertion that global warming did not play a part in the record warmth is not correct. The 2015-2016 El Nino started from a higher ‘platform,’ so it was much easier for to produce a record. ”
More generally, the key point is that what matters is the long-term global warming trend, and the mere end of El Niño certainly can’t refute that. Nobody is claiming that global warming means every year, or every month, will be hotter than the next. There is plenty of natural variability in the system which in fact ensures this won’t be the case.
And this is why, contra Breitbart’s claim about “icy silence,” scientists simply may not find the occurrence of cooling following El Niño to be a very big deal, or even necessarily worth remarking upon.
“It is normal and predictable that global temperature will fall after a strong El Nino,” explains former NASA climate researcher James Hansen, now at Columbia. “The natural oscillation of Pacific Ocean temperature associated with the El Niño/La Niña cycle adds on top of the more steady global warming trend due to increasing greenhouse gases. Global temperature with each successive El Niño is warmer than during the prior El Niño. Similarly, global temperature during each successive La Niña (the cool portion of the Pacific Ocean cycle) is warmer than the prior one — this is easy to see in the temperature record because of the strong greenhouse-gas-driven warming trend that has existed since about 1970.”
“The past 18 months have shattered global temperature records,” adds Ed Hawkins, a climate researcher at the University of Reading in the UK. “The dominant cause is the long-term increase in temperatures due to human activities but global temperatures in individual years and months also fluctuate due to weather patterns and factors such as El Niño.”
“We expect global temperatures to drop slightly as El Niño events fade, so it is unlikely that 2017 will set new records, but it will still be one of the warmest years since records began,” Hawkins continued.
Hawkins also created and tweeted out this graphic in order to underscore that the long-term trend is one of warming, whatever the short-term fluctuations may be:
Still, with the recent close of an El Niño, we could be in for a battery of claims about cooler temperatures. How do we know? Because it has happened before.
The arguments about a global warming “hiatus” or “pause” that dominated circa 2012 and 2013 were focused on a period following the powerful 1997-1998 El Niño, after which the rate of subsequent warming naturally appeared somewhat less. That was especially the case if you took the very warm year of 1998 as the starting point for an analysis of the temperature trend — because you were then starting at a high point, with a very warm year.
But as the United Nations’ Intergovernmental Panel on Climate change explained in 2013, that’s questionable reasoning because, again, it’s basically a form of cherry-picking:
In addition to robust multi-decadal warming, global mean surface temperature exhibits substantial decadal and interannual variability. Due to natural variability, trends based on short records are very sensitive to the beginning and end dates and do not in general reflect long-term climate trends. As one example, the rate of warming over the past 15 years (1998–2012; 0.05 [–0.05 to 0.15] °C per decade), which begins with a strong El Niño, is smaller than the rate calculated since 1951 (1951–2012; 0.12 [0.08 to 0.14] °C per decade).
Such statements are unlikely to persuade those who believe a dip in temperatures heralds a more permanent turn.
“This strategy will work for the next 200 years, even after there are palm trees, pineapple groves, and alligators in Alaska,” explains Stephan Lewandowsky, a psychology professor at the University of Bristol in the U.K. who has published on the errors of statistical reasoning lurking behind in claims of the global warming ‘slowdown’ or ‘pause’ genre.
“Random variation will never cease and it can always be exploited by political operatives. Scientists, by contrast, consider all the evidence, and when they do, then the fact that the Earth is warming appears virtually incontrovertible.”
This article incorrectly referred to The Daily Mail instead of the Mail on Sunday, which published the article by David Rose. This has been corrected.