The 5th Assessment Report of the IPCC, published in 2014, showed what appeared to be a curious lag in the upward trend of global warming. The observed global mean surface temperature (GMST) showed a smaller increasing trend over the period 1998-2012 than over the past 30 to 60 years. The reduction in the observed GMST trend was most marked in the Northern Hemisphere winter. The IPCC report called the lag a ‘hiatus’.
The GMST trend from 1850 to 2012 is shown in the chart below  In retrospect, the term ‘hiatus’ was perhaps a poor choice of words. It suggested that a global warming had ceased for a significant period of time—which was hardly the case as the chart shows. Nevertheless, for the small group of vocal people that categorically deny that global warming exists, the text in the IPCC report was seized upon as evidence that they were right all along: global warming was fiction. Yes, temperatures had gone up a bit; but now they were going down.
Climate scientists were puzzled by the ‘hiatus’. None of the sophisticated climate models predicted this slowing trend. The IPCC report suggested three possible explanations: (a) internal climate variability, (b) missing or incorrect radiative forcing or (c) model response error. The scientists went back and checked the models and the data.
The Karl study
In June 2015, one of the groups re-analysing the data reported its findings. The reputable magazine Science published their results in a paper entitled: Possible artefacts of data biases in the recent global surface warming hiatus.. The lead author was Thomas Karl. The scientists: most of whom were based at NOAA—the US National Oceanographic and Atmospheric Administration, summarized their findings as follows
Much study has been devoted to other possible causes of an apparent decrease in the upward trend of global surface temperatures since 1998, a phenomenon that has been dubbed the global warming “hiatus”. Here we present an updated global surface temperature analysis that reveals that global trends are higher than those reported by the Intergovernmental Panel on Climate Change, especially in recent decades, and that the central estimate for the rate of warming during the first 15 years of the 2st century is at least as great as the last half of the 20th century. These results do not support the notion of a “slowdown” in the increase of global surface temperature.
So there was no hiatus. Lamar Smith, a Republican senator from Texas, and a vociferous denier of climate change, smelled a rat.
At the time of the publication of what was subsequently called the ‘Karl study’, Lamar Smith was Chairman of the influential House Committee on Science, Space and Technology. Even though he heads up the House Science committee, he is not a scientist. But he’s a good friend of the oil and gas industries—which have rewarded his support with more than $600,000 in campaign finance contributions during his career in Congress. 
The response to the Karl study from the Science committee (on which the Republicans had a majority) was described as “swift, sweeping and caustic in tone from the start.”
Smith wrote to the NOAA on July 14, 2015, berating Dr. Kathryn Sullivan, a former astronaut and the NOAA Administrator under the Obama Administration for not making the data used in the Karl study public—only to learn from NOAA that the data had been public for one year prior to the publication of the Karl study. Smith then issued a subpoena on October 13 to the Department of Commerce requesting internal communications between NOAA scientists regarding global temperature data. NOAA pushed back but eventually provided much of the documentation.
A month later on November 18, 2015, during a Science Committee hearing on the upcoming Paris climate talks, Lamar Smith alleged that NOAA’s scientists had altered the data to get politically correct results in an attempt to disprove the ‘hiatus’ in global temperature increases. Smith sensed a conspiracy: suggesting that the timing of the release of the Karl study was somehow part of a government plot, asserting: “NOAA conveniently issues its new release promoting this report just as the Obama administration was about to announce its extensive climate change regulations.”
Smith continued his investigations. On the same day, November 18, he sent a seventh letter to the Administration about the Karl study alleging that NOAA had rushed to publish the paper—an allegation which proved to be false since the paper had been reviewed twice, a process that had taken six months.
By this time there was strong blowback from several major US science organisations—including the American Association for the Advancement of Science, the American Chemical Society, the American Geophysical Union, the American Meteorological Society, the American Statistical Association, the Ecological Society of America, and the Geological Society of America. Writing to Chairman Smith in November 2015, they expressed grave concerns about the committee’s investigation into the Karl paper, describing it as an inquest, “despite a lack of public evidence of scientific misconduct.” They went on to say: “Disagreements about the interpretation of data, the methodology, and findings are part of daily scientific discourse. Scientists should not be subjected to fraud investigations or harassment simply for providing scientific results that some may see as politically controversial.” 
Enter stage left
The fuss was dying down—as it usually does when climate deniers can find nothing in the way of evidence or data to support their contrarian point of view—when, and just like in a Shakespeare play, a new character emerged from the shadows.
John Bates was a senior scientist at NOAA at the time Thomas Karl and his colleagues published the paper refuting the idea of a hiatus in the upward trending global temperatures. Bates knew all about the paper, its methodology, data analysis and its contentious findings—as he should, because he was the person who signed off on the paper before it was submitted to Science.
In February 2017, over a year after the paper was published in Science, Bates was quoted on a blog post as saying that he thought there were flaws in the way that data had been formatted, and in the way the data was archived. He was careful to stress that the data had not been manipulated and that he did not question the conclusions of the study.
Bates’ concerns about database management and accessibility were instantly repackaged by the sensational UK tabloid media and trumpeted in Britain’s Daily Mail on February 4, 2017, under the headline “Exposed: How world leaders were duped into investing billions over manipulated global warming data”.
Chairman Lamar Smith wasted no time. In fact, it is clear he was ready and waiting. The day after the Mail on Sunday article was published, the Science Committee issued a Press Release almost as sensational as the Daily Mail’s: “Former NOAA Scientist Confirms Colleagues Manipulated Climate Records”, headlined the text issued by the Committee on February 5, 2017. It appears that Chairman Lamar Smith knew about the sensational UK tabloid press article well in advance: enough time for the Science Committee to prepare its companion text and issue it as a widely publicized press release the next day.
John Bates scrambled to set the record straight –and in two interviews on February 6, sought to stress that there was no manipulation of the data and that he was not questioning the conclusions of the study. “It’s not trumped up data in any way shape or form”, he protested. But by then it was too late: his protests of innocence were drowned out by the clamour of deniersphere war cries.
As is often the case, demonstrably false information about global warming and climate change, once released into the popular media and onto the platforms of the climate-denial front groups, continues to echo loudly for years. The conservative pseudo-scientific organisations set up with the help of funding from ExxonMobil had a field day.
For more information check out these sources:
 The text is from Climate Change 2013: The physical science basis. Chapter 9: Evaluation of climate models. Available at : www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter09_FINAL.pdf
 See Climate Change 2013. The IPCC 5th Assessment Report WG1. Available at: //www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_all_final.pdf
 Karl T.R, Arguez A., Huang B. et al.: Possible artifacts of data biases in the recent global surface warming hiatus. Science, Vol 348 issue 6242, pages 1469-1472. Accessed at //science.sciencemag.org/content/348/6242/1469/
5] Huffington Post: Meet the House science chairman who’s trying to put global warming research on ice. Accessed at: //www.washingtonpost.com/news/federal-eye/wp/2015/12/22/meet-the-house-science-committee-chairman-whos-trying-to-put-global-warming-research-on-ice/ See also the 2015 article in The Guardian: Lamar Smith, climate scientist witch hunter. Accessed at: //theguardian.com/environment/climate-consensus-97-per-cent/2015/nov/11/lamr-smith-climate-scientist -witch-hunter/
 Report of the Democratic staff of the House Committee on Science, Space & Technology for Democratic Members and Staff: Much ado about nothing: A minority review of the majority’s climate science investigation. March 2017.