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Risbey 2018 Environ. Res. Lett This is a repository copy of A fluctuation in surface temperature in historical context : Reassessment and retrospective on the evidence. White Rose Research Online URL for this paper: https://eprints.whiterose.ac.uk/141679/ Version: Published Version Article: Risbey, James S., Lewandowsky, Stephan, Cowtan, Kevin orcid.org/0000-0002-0189-1437 et al. (4 more authors) (2018) A fluctuation in surface temperature in historical context : Reassessment and retrospective on the evidence. Environmental Research Letters. 123008. ISSN 1748-9326 https://doi.org/10.1088/1748-9326/aaf342 Reuse This article is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs (CC BY-NC-ND) licence. This licence only allows you to download this work and share it with others as long as you credit the authors, but you can’t change the article in any way or use it commercially. More information and the full terms of the licence here: https://creativecommons.org/licenses/ Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing [email protected] including the URL of the record and the reason for the withdrawal request. [email protected] https://eprints.whiterose.ac.uk/ Environmental Research Letters TOPICAL REVIEW • OPEN ACCESS Recent citations A fluctuation in surface temperature in historical - Influence and seepage: An evidence- resistant minority can affect public opinion context: reassessment and retrospective on the and scientific belief formation et al evidence Stephan Lewandowsky To cite this article: James S Risbey et al 2018 Environ. Res. Lett. 13 123008 View the article online for updates and enhancements. This content was downloaded from IP address 144.32.225.1 on 28/01/2019 at 11:02 Environ. Res. Lett. 13 (2018) 123008 https://doi.org/10.1088/1748-9326/aaf342 TOPICAL REVIEW A fluctuation in surface temperature in historical context: OPEN ACCESS reassessment and retrospective on the evidence RECEIVED 8 February 2017 James S Risbey1 , Stephan Lewandowsky1,2 , Kevin Cowtan3 , Naomi Oreskes4 , Stefan Rahmstorf5,6 , REVISED Ari Jokimäki7 and Grant Foster8 9 November 2018 1 CSIRO Oceans & Atmosphere, Hobart Tas, Australia ACCEPTED FOR PUBLICATION 2 23 November 2018 University of Bristol, Bristol, UK and University of Western Australia, Crawley, WA, Australia 3 Department of Chemistry, University of York, York, United Kingdom PUBLISHED 4 Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, United States of America 19 December 2018 5 Potsdam Institute for Climate Impacts Research, Potsdam, D14473, Germany 6 University of Potsdam, Potsdam, Germany Original content from this 7 Independent researcher, Finland work may be used under 8 1 Noyes Ct, Augusta, ME 04330, United States of America the terms of the Creative Commons Attribution 3.0 E-mail: [email protected] licence. Any further distribution of Keywords: climate variability, climate trends, temperature fluctuation, pause hiatus this work must maintain attribution to the author(s) and the title of the work, journal citation Abstract and DOI. This work reviews the literature on an alleged global warming ‘pause’ in global mean surface temperature (GMST) to determine how it has been defined, what time intervals are used to characterise it, what data are used to measure it, and what methods used to assess it. We test for ‘pauses’, both in the normally understood meaning of the term to mean no warming trend, as well as for a ‘pause’ defined as a substantially slower trend in GMST. The tests are carried out with the historical versions of GMST that existed for each pause-interval tested, and with current versions of each of the GMST datasets. 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 also with trends that are continuous with the data bordering the trend interval. We also compare results when appropriate allowance is made for the selection bias problem. The results show that there is little or no statistical evidence for a lack of trend or slower trend in GMST using either the historical data or the current data. The perception that there was a ‘pause’ in GMST was bolstered by earlier biases in the data in combination with incomplete statistical testing. ‘Nowadays any reference to polywater industrial revolution is imposing climate changes on is always tinged with ridicule, but ten timescales from decadal to centennial, and ultimately years ago many competent and experi- much longer too as the oceans and cryosphere respond enced scientists were quite convinced to the changes in Earth’s energy balance (Hansen et al of its reality. I can see no reason why 1985, Houghton et al 2001). The detection and the scientific and sociological issues attribution of greenhouse climate change (Mitchell raised by this unique episode should be et al 2001) deals with the identification of the ‘signal’ of shrouded in secrecy’—Felix Franks, the forced response to greenhouse gases from the Polywater. ‘noise’ of variability of climate that occurs on the same decadal and multidecadal timescales. The greenhouse climate signal is always accompanied to some degree ‘ ’ 1. Introduction by noise (variation) from other forcings of the climate system (such as due to changes in aerosol loading or The Earth’s climate varies on a vast range of temporal solar variations)(Marotzke and Forster 2015) and by scales (National Research Council 1982, 1995). The internal variations intrinsic to the coupled climate persistent increase in greenhouse gases since the system (O’Kane et al 2013). © 2018 The Author(s). Published by IOP Publishing Ltd Environ. Res. Lett. 13 (2018) 123008 J S Risbey et al In recent years there have been more than two evidence for the ‘pause’ in the observed GMST record, hundred articles in the climate literature discussing as it is now, and as it was at the time the research was the notion of a ‘pause’ or ‘hiatus’ in greenhouse warm- undertaken. ing that is variously alleged to have taken place some The review provides initial context by describing time in the past couple of decades (Lewandowsky et al temperature fluctuations in the climatological litera- 2016). The form of alleged climate ‘pause’ varies across ture and some issues in constructing observed series of the literature, but essentially involves calculation of a GMST. The consequences of the uncertainties in short-term trend in global mean surface temperature GMST are described for assessment of short-term (GMST) over a decade or two, which is then compared GMST trends. The review then proceeds by providing with either other periods in observed GMST (Stocker a series of retrospective constructions of short-term et al 2013), or with trends estimated from coupled cli- GMST trends on the basis of what was known about mate model projections (Fyfe et al 2013, Risbey et al uncertainty in each of the major GMST series at differ- 2014). This review addresses the former issue (com- ent points in time compared to what is known now parison of observed trends), while a companion about uncertainty in each of these series. This retro- review (Lewandowsky et al 2018) addresses the com- spective analysis provides a framework in which to parison with climate model expectations of trends. assess what was known (or could have been known at When it first emerged, the concept of a global the time) when assessing the evidence for a ‘pause’ in warming ‘pause’ was mostly cast in terms of the obser- global warming. The retrospective (historical) assess- vational record as a period of slower than average ment of trends uses the versions of the GMST data that warming (e.g. Stocker et al 2013). With time, usage existed at the times when researchers carried out their broadened to include a comparison of observed assessments of trend-intervals. warming rates with those inferred from model projec- Because the literature on the ‘pause’ is now so vast, tions. The observations-based view of the ‘pause’ is the review treats the literature primarily as a database perhaps more intuitively accessible, whereas the for statistical assessments. The sets of definitions model-comparison view of the ‘pause’ allows for more implied for the ‘pause’ can be inferred from the pause- complexity in matching variations in the forcing and literature, which provides the range of intervals against the (model simulated) response to that forcing with which to assess potential pauses. We have attempted to observed trends. Neither definition turns out to be summarise some of the key messages and the approach straight-forward in practice. We concern ourselves to statistical methods in this literature, but do not pro- fi exclusively here with the rst (observations-based) vide a chronological assessment of individual con- ‘ ’ view of the pause . As such, we do not consider the tributions in the sense more common in reviews. Our role of climate forcing, and we do not conduct any concern is with the definitions, data, and methods fl analysis directed at a causal understanding of uctua- used and their implications for the conclusions drawn. tions in GMST (which would require the use of cli- mate models). We do not discount the worth of the model-comparison view of the ‘pause’, but the issues 2. Climate fluctuations past and present are complex enough that they require separate exam- ination (Lewandowsky et al 2018). While the observa- The field of climatology has long recognized that tions-based view of the ‘pause’ is intuitively appealing climate varies on decadal and longer time scales. The in that one can ostensibly ‘see’ a slowing of warming concept of a ‘climate normal’ was introduced in the rate in (parts of) the GMST record, mere description is early 20th century as a 30 year record or average of not the same as statistical evidence.
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