A fluctuation in surface temperature in historical context: reassessment and retrospective on the evidence
This work reviews the literature on an alleged global warming ‘pause’ in globalmean surface temperature (GMST) to determine how it has been defined, what time intervals are used to characterise it, what data are used tomeasure it, andwhatmethods used to assess it.We test for ‘pauses’, both in the normally understoodmeaning of the term tomean nowarming trend, as well as for a ‘pause’ defined as a substantially slower trend inGMST. The tests are carried outwith the historical versions of GMST that existed for each pause-interval tested, andwith current versions of each of theGMSTdatasets. The tests are conducted following the common (but questionable) practice of breaking the linear fit at the start of the trend interval (‘broken’ trends), and alsowith trends that are continuouswith the data bordering the trend interval.We also compare results when appropriate allowance ismade for the selection bias problem. The results show that there is little or no statistical evidence for a lack of trend or slower trend inGMSTusing either the historical data or the current data. The perception that therewas a ‘pause’ inGMSTwas bolstered by earlier biases in the data in combinationwith incomplete statistical testing. ‘Nowadays any reference to polywater is always tinged with ridicule, but ten years ago many competent and experienced scientists were quite convinced of its reality. I can see no reason why the scientific and sociological issues raised by this unique episode should be shrouded in secrecy’—Felix Franks, Polywater.