Global warming hiatus

[4] Research reported in July 2015 on an updated NOAA dataset[8][10] casts doubt on the existence of a hiatus, and it finds no indication of a slowdown even in earlier years.

The warmth of 2015 largely ended any remaining scientific credibility of claims that the supposed "hiatus" since 1998 had any significance for the long-term warming trend,[24] and 2016 was even slightly warmer.

In January 2017, a study published in the journal Science Advances cast further doubt on the existence of a recent pause, with more evidence that ocean temperatures have been underestimated.

[25][26] An April 2017 study found the data consistent with a steady warming trend globally since the 1970s, with fluctuations within the expected range of short term variability.

[42] The decade to the end of 2010 was again the warmest on record, but David Rose in the Mail on Sunday argued that, excluding the 1998 "blip", global temperatures had been flat for 15 years.

[43] A November 2011 study by statistician Grant Foster and Stefan Rahmstorf showed that after allowing for known short-term variability, there had been unabated warming since 1998 with no reduction from the rate over the preceding decade.

Research cited in the report had to be published by 15 March, which excluded more recent work such as a paper by NCAR scientists including Kevin E. Trenberth indicating that increased heat was going into ocean depths.

[2] A month before formal AR5 publication, a leaked draft of the report noted that "Models do not generally reproduce the observed reduction in surface warming trend over the last 10–15 years", but lacked clear explanations, and attracted wide media coverage.

[2] On 16 August Reuters said the "panel will try to explain why global temperatures, while still increasing, have risen more slowly since about 1998 even though greenhouse gas concentrations have hit repeated record highs in that time".

[52] The BBC on 19 August reported IPCC warnings that the final text would vary, and said "The panel will also outline why global temperatures have been rising more slowly since 1998, a controversial slowdown that scientists have been struggling to explain."

It said the possibility that climate sensitivity was lower than previous estimates had been argued by "many sceptics" as a key factor, and "a good reason not to believe the more extreme predictions of those they dismiss as warmist conspirators.

"[53] Coverage varied: on 22 August the National Geographic said the "draft IPCC report also dismisses a recent slowdown in global warming, attributing it to short-term factors.

"[54] On 26 September, the day before formal publication, CBC News quoted The Heritage Foundation under the headline "Climate change reports temperature hiatus fuels skeptics".

[2][56] Even Nature headlined their news report "IPCC: Despite hiatus, climate change here to stay", though it said that "the 'hiatus' since the record hot year of 1998 — probably due to increased heat uptake by the oceans — is no sign that global warming has stopped, as some would like to hope", and quoted climatologist Thomas Stocker saying that "Comparing short-term observations with long-term model projections is inappropriate", and adding "We know that there is a lot of natural fluctuation in the climate system.

[57] In a statement to the press in March 2016, Professor David Vaughan of the British Antarctic Survey said that recent increases in global temperature were not due to an unusually severe El Niño, but that the opposite is true.

[65] A study published in January 2015 proposed that the hiatus resulted from a 60-year oscillatory pattern of natural variability associated with the AMO and PDO, interacting with a secular warming trend due mainly to human caused increases in greenhouse gas levels.

[66] One proposal is that the hiatus was a part of natural climate variability, specifically related to decadal cooling in the eastern equatorial Pacific in the La Niña phase of the El Niño–Southern Oscillation (ENSO).

[17][63] A March 2014 study found that climate models assuming natural variability which matched subsequent observations of ENSO phasing had produced realistic estimates of 15-year trends.

A new "delayed oscillator theory" of the North Atlantic decadal-scale air-sea coupling was further proposed in 2015[71] to understand the underlying physical mechanisms of the 60-80-year-quasi-periodic natural climate multidecadal variability.

According to an October 6, 2014 NASA press release related to the papers, "One of the most prominent ideas is that the bottom half of the ocean is taking up the slack, but supporting evidence is slim."

"[74] That the oceans warmed in the past significantly faster than we thought would imply that the effects of climate change could be worse than currently expected, placing the planet's sensitivity to CO2 toward the higher end of its possible range.

[80] Several studies have proposed that possible slower surface warming during this period was caused in part by increased sulfur emissions from volcanic activity.

[87][88] Spurious differences in observed warming rates may also arise from the mathematics of trend analysis itself, particularly when the study period is brief and regression assumptions are violated.

[89] Two independent studies published in August 2014 concluded that, once surface temperatures start rising again, it is most likely that "they will keep going up without a break for the rest of the century, unless we cut greenhouse gas emissions.

[91] Maher et al found that under the existing and projected high rates of greenhouse gas emissions there is little chance of another hiatus decade occurring after 2030, even if there were a large volcanic eruption after that time.

[92] A joint report from the UK Royal Society and the US National Academy of Sciences in February 2014 said that there is no "pause" in climate change and that the temporary and short-term slowdown in the rate of increase in average global surface temperatures in the non-polar regions is likely to start accelerating again in the near future.

With deliberately cherry picking appropriate time periods, here 1998-2012, a "pause" can be created, even when there is an ongoing warming trend.
Temperature data from various scientific organizations worldwide show a high correlation regarding the progress and extent of global warming.
Amardeo Sarma lecturing about climate change denialism at the European Skeptics Congress, hosted by the Association for Skeptical Enquiry .
One deceptive approach is cherry picking data from short time periods to assert that global average temperatures are not rising. Blue trendlines show short-term countertrends that mask longer-term warming trends that are shown by red trendlines . [ 34 ] Such representations have been applied to the so-called global warming hiatus ( blue rectangle with blue dots , in upper right). [ 35 ]
Global (land and ocean) surface temperature anomaly time series with new analysis (solid black) versus no corrections for time-dependent biases (blue). The new analysis shows a long-term trend since 1880 that is less than that which would be estimated without corrections. And, in particular, the trend since 1998 is not significantly different from that found for the new analysis since 1880. [ 8 ] [ 60 ] [ 10 ]