This story has been updated.
Matters seem to have escalated in the current dispute between Rep. Lamar Smith (R-Texas), chair of the House Committee on Science, Space, and Technology, and the National Oceanic and Atmospheric Administration.
As our own Joby Warrick and Lisa Rein have reported, Smith sent subpoenas to NOAA several weeks ago, seeking internal emails and documents regarding a blockbuster June study by its scientists, which had appeared to erase the notion of a global warming “pause.” This notion — that global warming had “paused” or seen a “hiatus” between 1998 and 2012 — was a very influential line of climate change doubter attack against the 2013 findings of the United Nations’ Intergovernmental Panel on Climate Change, especially since the body itself lent some credence to the idea. So have many scientific publications.
Now Smith is contending that the NOAA study, led by Thomas Karl, the director of NOAA’s National Centers for Environmental Information, was “rushed to publication,” Rein reports. She also reports that Penny Pritzker, President Obama’s Commerce Secretary (whose department contains NOAA), could be subpoenaed in relation to the inquiry.
Here’s the thing, though. Even if you feel that federal scientists ought to turn over their emails in this case (not doing so is matter of principle for many science organizations, and scientists themselves) the fact is that the “pause,” even if it existed, was never a good reason not to worry about global warming. And now, with 2015 temperatures surging, the “pause” debate seems more than a little dated.
Let’s take these two points in order.
The so-called ‘pause’ was never a reason to doubt global warming. The canonical description of the “pause,” at least by a major scientific body, was made in 2013 by the U.N.’s Intergovernmental Panel on Climate Change, which stated the following:
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).
You will note that this is not exactly a wild declaration that global warming has stopped. Rather, it is an observation that if you take a relatively short time period in the global temperature record, and in particular, if you start that time period with a very hot year, then the trend looks different than the trend over a longer period. Indeed, the same IPCC report said that global warming is “unequivocal” and that it is “extremely likely” that humans are its “dominant” cause.
What was striking about the paper by Thomas Karl and his NOAA colleagues, now at the center of Smith’s inquiry, is the contention that not even the IPCC’s limited statement above is correct. After making a number of corrections and adjustments to the influential NOAA temperature dataset to deal with what they describe as biases in some types of data, and also extending the record through 2014 (currently the official hottest year ever), the researchers noted the following:
Our new analysis now shows that the trend over the period 1950–1999, a time widely agreed as having significant anthropogenic global warming, is 0.113°C [per decade], which is virtually indistinguishable from the trend over the period 2000–2014 (0.116°C [per decade]). Even starting a trend calculation with 1998, the extremely warm El Niño year that is often used as the beginning of the “hiatus,” our global temperature trend (1998–2014) is 0.106°C [per decade]—and we know that is an underestimate because of incomplete coverage over the Arctic.
In essence, then, Karl and his colleagues — if they’re right — turned a curious but relatively inconsequential “pause” into nothing at all. Either way, though, it doesn’t change the following conclusion: the pause was perhaps a scientific mystery worth exploring and explaining, but no reason to doubt the overall global warming problem.
“There has never been any evidence for a significant change in the long term trend, so any short term variations are (were) basically of academic interest only,” explains Gavin Schmidt, director of the NASA Goddard Institute for Space Studies, by email. He provided this figure, which he had previously tweeted, to show as much:
And indeed, many scientific studies have sought to examine precisely why temperatures in the decade of the 2000s may have been somewhat slower to rise, often focusing on a phenomenon of heat burial deep in the Pacific Ocean, a temporary and natural phenomenon expected to reverse in time. Thus, the discussion around the “pause,” while often used for political ends, also generated interesting research and, no doubt, a better understanding of the many natural factors that can modulate human-caused climate change.
Pause or not, we’re now headed to new temperature peaks. It is surely possible, then, that Karl et al are wrong, and there really was a pause. Kevin Trenberth, a researcher at the National Center for Atmospheric Research, argued precisely this point in a paper in Science disagreeing with Karl and his team of NOAA researchers, and pointing to real trends in the Pacific. Debate over this matter will likely continue for some time.
But in that very paper, Trenberth also observed that “the upward trend has resumed in 2014, now the warmest year on record, with 2015 temperatures on course for another record-hot year.”
NASA’s Schmidt agrees. “Given that long term trend, it was inevitable that we’d be heading into record territory with the next El Niño – and boy has that happened,” he said, referencing the image above.
Which brings us to the present. Debating the “pause” seems rather odd right now, with the global average temperature pushing new highs. Even though it’s only November and not all of the data are in, 2015 is now considered very likely to be the globe’s hottest year on record, enhanced by a very strong El Nino event (just like 1998 was).
“There can no longer be any meaningful doubt that 2015 will be the Earth’s warmest year on record, at an entirely different level from the previous warmest years,” noted our own Capital Weather Gang, analyzing the latest monthly global temperature release from, that’s right, NOAA. NASA data, meanwhile, show that October of 2015 had the biggest temperature anomaly of any month ever recorded by the agency.
This would mean that we would have two record years in a row — with 2015 blowing out the prior record year, 2014.
So what would that mean for the debate over the “pause,” which boils down to an analysis of the rate of change?
While you need a statistical analysis like the IPCC’s or NOAA’s to declare a slowdown (or the end of one), it’s worth noting that a group of scientists with the UK Met Office — which still does support the idea of a pause or hiatus — noted in September that “there are signs in the observations and near term climate predictions that are consistent with a resumption of warming.” The office noted in particular the strong warmth this year and suggested that 2016 could be similar.
As the analysis added:
Record or near record temperatures last year and so far this year, along with the expected warming effects of El Niño, mean that decadal temperature trends are likely to increase. Barring a large volcanic eruption or a very sudden return to La Niña or negative [Atlantic Multidecadal Oscillation] conditions which could temporarily cool climate, ten year global average warming rates are likely to return to late 20th century levels within the next two years.
Michael Mann, a researcher at Penn State University who has also attributed a global warming slowdown to Pacific cycles, similarly told me earlier this year that the slowdown represented “part of a short-term excursion that is likely to reverse in the years ahead.” A study earlier this year by scientists with the Pacific Northwest National Laboratory went even farther and predicted that “the world is now entering a regime where background rates of climate change will be well above historical averages until at least mid-century.”
If these analyses prove to be right, then one lesson of the whole “pause” saga may be that global warming, in Trenberth’s words, is “more like a rising staircase than a monotonic rise.” El Ninos are often among the warmest years, but they don’t come every year. But when you add a succession of El Ninos, of varying strengths, to a rising global average temperature trend, then you find that a major El Nino in 2015 will be hotter than a major El Nino in 1998.
Thus, what may look like a pause if you run your analysis from 1998 through 2012, looks like just plain global warming if you end your analysis in 2015. And whoever is right about the “pause,” there’s simply little doubt that we have a long term warming problem on our hands.
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