Rep. Lamar Smith at a recent hearing claimed a new study published in the journal Nature Climate Change “confirms the halt in global warming.” It doesn’t. In fact, the authors of the paper write, “We do not believe that warming has ceased.”
Smith, chairman of the House Committee on Science, Space, and Technology and longtime climate change skeptic, used the Nature study as ammunition against the National Oceanic and Atmospheric Administration in an ongoing battle over the validity of a paper that NOAA researchers published in the journal Science last June.
While the Nature study, published online in late February, claims there was a “slowdown” in the rate of global warming in the early 21st century, the Science paper argues there was not. But the studies compared different time periods. Both studies agree that there was no complete halt in global warming and the long-term warming trend remains unabated.
At the March 16 House hearing, Smith also continued to criticize the Science paper. He said the paper was “prematurely published,” but the editor-in-chief of Science told us Smith’s claim is “baseless and without merit.” Smith also said that the NOAA researchers used “controversial methods” in their study, but the authors of the Nature paper cited by Smith said this wasn’t the case. In fact, they cite the Science paper as having “high scientific value.”
Overall, each study asked different scientific questions, the answers to which can both remain valid and correct, according to the Nature authors themselves.
Smith vs. NOAA
This is not the first time Smith, a Republican from Texas, has made false statements about climate science and the so-called “Karl study,” named after Thomas R. Karl, director of NOAA’s National Centers for Environmental Information and the Science paper’s lead author.
As we’ve written before, Smith claimed in October 2015 that “climate data has clearly showed no warming for the past two decades” and that NOAA scientists “altered the data” to get the results they presented in the Science study.
Motivated to quell what he considers the NOAA and Obama administration’s “extreme climate change agenda,” Smith used the House science committee’s subpoena power on Oct. 13 to obtain internal communications at NOAA regarding the Karl study. NOAA has provided the committee with some documents and emails, though Smith continues to request more information.
In the battle’s latest episode, NOAA Administrator Kathryn Sullivan testified before the House science committee on March 16 on NOAA’s 2017 budget. Again, Smith brought up the Karl study, claiming it was “prematurely published” and used “controversial new methods,” among other things.
During the hearing, Sullivan countered by stating that the final timing of any publication is “at the discretion of the publication itself.” She also said Science “scrubbed this paper with extra diligence” due to the “interest in this matter.”
According to Marcia McNutt, editor-in-chief at Science, Smith is wrong and Sullivan is right. In fact, McNutt told us by email, “Any suggestion that the review of this paper was ‘rushed’ is baseless and without merit.”
McNutt added that “knowing that this report’s results disputed the existence of a 21st century global warming slowdown described in previous studies, Science took extra care to assure even more rigorous review and evaluation than normal.”
When asked to provide evidence that NOAA had prematurely published the Karl study, a committee aide for Smith pointed us to a Nov. 23, 2015, Washington Post article. In that article, Thomas Peterson, an author of the Science study and retired NOAA climate scientist, describes “internal tensions” between NOAA scientists and engineers over delays related to the programs used to process the climate data. But in the same piece, Peterson is quoted as stating that the research was not rushed. “Indeed just the opposite is true,” he told the Post.
Smith made a few new claims during the March 16 budget hearing as well. He said, “A new peer-reviewed study, published in the journal Nature, confirms the halt in global warming. According to one of the study’s lead authors, it ‘essentially refutes’ NOAA’s study.” Smith also repeatedly asked Sullivan to side with either the Science or the Nature study’s findings because he claimed both can’t be “correct” or “valid.”
First off, the two papers’ disagreement was on whether the rate of warming has slowed in the first 15 years of the 21st century, not whether warming has halted, as Smith claimed.
Second, John Fyfe, lead author of the Nature paper, told us in an email that Smith took his comment during an interview with the website Climate Central out of context. “It would be incorrect to interpret [the ‘essentially refutes’] quote as indicating that Fyfe et al. refuted the Karl et al. study in its entirety.” He said, “As we said in our Commentary we view the Karl et al. study as being of ‘high scientific value.’ ”
Third, according to McNutt and the Nature authors, both papers could, in fact, remain valid and correct. For example, Gerald Meehl, an author on the Nature paper and climate scientist at the National Center for Atmospheric Research, pointed us to a segment of an article with Environment & Energy Publishing, which states “both comparisons are valid … and provide answers to different questions.”
In the following section we’ll explain the similarities and differences between the two papers’ methods and results and why both can remain valid.
Science vs. Nature
Both the Science and the Nature papers begin by mentioning the Intergovernmental Panel on Climate Change’s description of a surface warming slowdown between 1998 and 2012 in its Fifth Assessment Report. Both papers also note that researchers use “hiatus” to describe this slowdown in the scientific literature — a point Smith’s committee aide made to us. But technically the rate of global warming never completely halted during this period, as both papers state.
For this reason, the authors of the Nature paper write that it’s “unfortunate” that the 21st century warming trend has been framed as having “stalled,” “stopped,” “paused” or “entered a ‘hiatus.’ ” While “[j]ust exactly how such changes should be referred to is open to debate,” the authors suggest “reduced rate of warming,” “decadal fluctuation” and “temporary slowdown” as some possibilities.
Both papers diverge when it comes to the specific questions the researchers asked, and, accordingly, how they quantified the slowdown.
The authors of the Science paper compared the rate of warming during the period between 2000 and 2014 with that of 1951 to 1999, though they also investigated trends in warming dating back to 1880.
The Nature authors, alternatively, compared the warming rate of 2001 to 2014 with a shorter period — 1972 to 2001.
The rationale for using different time periods is tied, at least in part, to the ultimate aim of each study.
The Science study was designed to determine if the global warming trend for “the first 15 years of the 21st century is at least as great as the last half of the 20th century.” It found there was no “slowdown” in global warming compared with this 50-year period.
The Nature study, on the other hand, strove to figure out whether the rates of global warming fluctuate every few decades, so the authors compared the first 15 years of the 21st century with a shorter time period. They reported that the rate had slowed down from 1950 to 1972, then sped up from 1972 to 2001, and then slowed again from 2001 to 2014. “A warming slowdown is thus clear in observations; it is also clear that it has been a ‘slowdown’, not a ‘stop,’ ” the study concluded.
Meehl told us by email that it was mainly the Karl study’s “interpretation of different trend lengths [discussed above] that we took issue with.”
However, Meehl said he did not find the Karl study’s methods to be “controversial.” The adjustments the NOAA scientists made to their data, which Smith has criticized, “were fairly minor,” added Meehl, and involved calibrating different sets of data to each other.
For example, data on sea surface temperatures alone can come from buoys, ship engine-intake systems and buckets dropped off the side of a ship. As the Science study states, “ship data are systematically warmer than the buoy data,” so adjustments need to be made to calibrate them to each other.
The same inconsistencies occur when data are collected from different land stations. In fact, the Nature paper describes the Karl study’s identification and correction of these data “errors and inhomogeneities” as “of high scientific value.”
Michael Mann, a climate scientist at Penn State University and an author on the Nature paper, wrote Smith an open letter on March 3, which directly addressed the chairman’s false claims.
In his letter, which was posted on Facebook, Mann wrote: “Please don’t misrepresent our recent Nature Climate Change commentary. Our study does NOT support the notion of a ‘pause’ in global warming, only a *temporary slowdown*, which was due to natural factors, and has now ended.”
In sum, based on their different questions and correspondingly different time period comparisons, the Science and Nature studies came to different, though equally valid, conclusions about the warming rate in the early 21st century. Regardless, neither paper supported a halt in global warming, as Smith claimed.
Editor’s Note: SciCheck is made possible by a grant from the Stanton Foundation.