Extreme Temperature Diary- December 23rd, 2018/ Topic: A Recent Global Warming Hiatus? Much Ado About Nothing

guyonclimate_mi5tor

Sunday December 23rd… Dear Diary. The main purpose of this ongoing post will be to track United States extreme or record temperatures related to climate change. Any reports I see of ETs will be listed below the main topic of the day. I’ll refer to extreme or record temperatures as ETs (not extraterrestrials)😊. 

A Recent Global Warming Hiatus? Science Says No

This item is about a week old but probably needs to be broken down a bit more for educational purposes. Most in the denial camp claimed that global warming slowed down from 1998 until about 2014 (The period in between record strong El Ninos), even stating that a cooling trend was underway. Two new studies cement the scientific claim that there was no global warming Hiatus:

 

Here is a link to one of the studies published on 12/19/18:

http://iopscience.iop.org/article/10.1088/1748-9326/aaf342/meta#erlaaf342s3

Here are some quoted excerpts from this lengthy paper: 

Given that climatologists were well aware that GMST fluctuates on decadal (and longer) time scales, the emergence of a claim in the climate literature from about 2009 that climate change as represented by GMST had entered a ‘pause’ or ‘hiatus’ was a strong claim. In effect, the claim was that the most recent decadal-scale fluctuation in GMST was somehow extraordinary or substantially different from past GMST fluctuations. This interpretation is consistent with the fact that the fluctuation was given a name (‘pause’ or ‘hiatus’) and with the claim frequently made in pause-papers that this fluctuation (but not others) was not consistent with the GMST response to increases in greenhouse gases (Lewandowsky et al 2016).

In order to assess the claims made about this particular fluctuation in the literature, we identified a set of 224 peer reviewed articles in the climate literature (through 2016) that referred to a ‘pause’ or ‘hiatus’ in GMST in the title or abstract. From this larger set, we constructed a subset of papers that defined a start and end date for any alleged pause, and which specified the GMST data used for analysis. This is the minimum amount of information needed to reproduce and test the claims of a ‘pause’ in these papers. The application of these criteria reduced the subset to 90 papers, which is the analysis subset used here and denoted ‘pause-papers’. The number of papers published each year on the ‘pause’ is shown in figure 1(a) and rises substantially from 2013. The ‘pause-research period’ (as reflected by published papers) extends from about 2010 through the present.

 

 

Figure 1. Histograms summarising characteristics of ‘pause’ definitions in the literature. Panel (a) shows the number of pause-papers published in the peer-reviewed literature each year between 2009 and 2016. (b) Is a histogram of the set of start dates for the pause-period inferred from the pause-papers. (c) Is a histogram of the durations of the pause-periods inferred from the pause-papers. (d) Is a histogram of the pause-period, which shows the number of times each year in the year axis is included in the pause-period across all the pause-papers.

The pause-period was selected by the authors of pause-studies to correspond to a period where the rate of warming is slower than the average longer-term warming rate. This period can be highlighted and placed in context by showing a sliding sequence of short-term trends in GMST through the modern period (figure 2). By colour-coding the trends as red/blue according to whether they are warming faster/slower than the longer-term rate of warming, it is apparent that there are persistent periods of faster and slower than average warming. The pause-period in the pause-literature shows up as the second slower than average warming period on the plot. The identification of a period of slower than average warming does not suffice to demonstrate that such a period is statistically unusual. For that more formal criteria would need to be applied.

 

Figure 2. Time series of annual GMST anomaly from Cowtan and Way (stair plot). The black dashed line is a linear fit over the period. The thin red and blue lines are linear 11-year trend lines sliding over the period. These lines are red/blue when the slope of the 11-year fit is greater/less than the slope of the longer-term dash line. The choice of interval length here (11 years) is arbitrary, but all interval lengths used in the pause-papers will exhibit periods of faster and slower than average trend.

Different criteria have been used to constitute a ‘pause’ in the pause-papers. Most early papers employ it in a manner consistent with the common sense usage to signify an absence of a warming trend (no trend). Later papers, however, often use it to signify a reduction in the warming trend, i.e. a slower than normal trend. This shift in definitions, by itself, might indicate a problem, as it shows that even at the time, the scientific community was unclear and inconsistent as to what the object of study was. In this paper we test both claims. To illustrate these definitions we have redrawn figure 2 in idealised form in figure 3. Here, we represent the GMST series (without interannual variation) in its idealised form as undergoing regular fluctuations about a long-term mean warming rate (the dashed black line). The fluctuating line is again coloured red when the trend is greater (warming faster) than the longer-term mean trend and blue when it is smaller (warming slower) than the mean trend. One expects short-term trends to fluctuate faster and slower through time than the longer-term trend as illustrated here. There has been little research attention on the faster fluctuation that preceded the slower fluctuation that is the target of the pause-papers (Rahmstorf et al 2007, Lewandowsky et al 2015a).

 

Figure 3. Idealised schematic of a smoothed global mean surface temperature series (blue/red line). The series is a linear trend plus sinusoidal variation to mimic multidecadal fluctuations. The dashed line is the linear fit component. The series is coloured red/blue when the local gradient is steeper/shallower than the linear fit. The inset boxes show a red segment where the slope is compared to the long-term linear slope, and a blue segment where the slope is compared to either the long term linear slope or to zero slope.

The ‘slow’ trend view of the pause (figure 3) is seldom defined formally in the pause-literature. It could refer (as in Stocker et al 2013) to a meaningful change in the trend (slope) of GMST in the pause-period relative to the longer-term trend that prevailed prior to the pause-period (change in trend). Alternatively, it could refer to a claim that the trend during the pause-period is unusual relative to trends of a similar length during the modern warming period (unusual trend). For example, the pause-period fluctuation in figures 2 and 3 could be assessed against slower than average fluctuation periods such as the prior one in the 1980s. We will restrict this comparison to fluctuations that occur through the period that GMST has been fairly steadily increasing (with fluctuations) to avoid including a large sample of the early record when the longer-term warming trend was much weaker. An objective way to determine how far back to include past fluctuations is to assess the GMST record for meaningful ‘change-points’ in trend (Cahill et al 2015). We have performed change-point analysis on each of the GMST records used here and find changes in each dataset near 1970. This is consistent with other analyses and with the choice often made in the literature to define the modern warming period. In all the analyses to follow we use the change-points (near 1970) particular to each dataset in assessing how unusual the recent slower fluctuation is.

The time series of GMST from five of the principal groups constructing records of GMST is shown in figure 4. The five series exhibit clear variability at interannual and decadal to multidecadal scales, with a long-term warming trend. While there are some differences between the series as represented by the five different datasets here, they display very similar variability and long-term trends. As such, the differences between the datasets have historically been more of interest to specialists in the field, as they yield very similar views of the climate response to greenhouse gases.

 

Figure 4. Annual mean global mean surface temperature series for each of the datasets shown based on versions of each set at the end of 2016. The baseline-period for calculating anomalies in each data set is 1981–2010.

Figure 4 pictorially shows that there was no pause. Skipping down to conclusions:

In learning lessons from the pause-episode in the GMST record we can describe some elements of the pause-timeline and its consequences. The origin of the ‘pause’ lay in contrarian narratives about the climate (Mooney 2013, Lewandowsky et al 2015a). With the ‘pause’ (or ‘hiatus’), a false narrative about an alleged inconsistency between natural fluctuations of global temperature and ongoing global warming was inserted into climate discussion. Once the notion of a ‘pause’ was established, some of the major journals gave prominent feature to articles about it (Nature 2017). The IPCC formalised the ‘pause/hiatus’ for the climate community in its 5th assessment report by defining and accepting it as an observed fact about the climate system (Stocker et al 2013) [Box TS.3]. Many climatologists also adopted the ‘pause’ or ‘hiatus’ into their own language about climate change. The adoption of these terms by the mainstream research community gave the ‘pause’ further legitimacy, even though they often explained that it was not unusual in the context of natural variability. Whether intended or not, this fed the public narrative that there was a ‘pause’ in global warming (Mooney 2013). To complete the cycle, researchers and climate institutions have now declared the pause to be ‘over’, thereby reinforcing the notion that it once existed (Xie and Kosaka 2017, Met Office 2017).

In hindsight, with current GMST datasets, there is no statistical evidence for a ‘pause’. That is the case regardless of which dataset is used and even using statistical tests that inflate the significance of the results. Global warming did not pause in observations (according to any common usage of the term or in statistical terms), but clearly we need to understand how and why scientists came to the conclusion that it had in order to avoid future episodes of this kind. To this end, we pose a series of counterfactual questions about the evidence on the ‘pause’ in GMST.

From the linked Inside Climate News Article:

“When things don’t look quite how you expect, you dive into it,” said Gavin Schmidt, a climate scientist and director of the NASA Goddard Institute for Space Studies. “People looked into it, and it turned out to be nothing.”

Missing Arctic data was part of the problem. In the end, the idea of a pause, often cited by climate policy opponents, didn’t hold up to statistical testing.

A Lack of Arctic Data:

The notion of a pause in warming from approximately 1998 to 2012, was fueled in part by incomplete data and erroneous projections that have since been corrected, the studies conclude.

It’s long been obvious that if there had been any blip in the trends it was temporary. The years that followed have hit new temperature records.

And new evidence has made clear why some were fooled.

Scientists know, for example, that the Arctic is warming at a faster rate than the planet as a whole, but there weren’t enough temperature observations from the Arctic in the early 2000s to accurately measure the changes that were occurring there. As a result, data sets on global temperature tended to omit the Arctic until recently, when researchers came up with a better way to extrapolate data from the region.

“We simply didn’t have all the information available at the time,” Stephan Lewandowsky, a researcher at the University of Bristol and lead author of the climate modeling report said.

“There was a natural slowdown in the rate of warming during roughly the decade of the 2000s due to a combination of volcanic influences and internal climate variability, but there was no actual ‘hiatus’ or ‘pause’ in warming,” Michael Mann, director of the Earth System Science Center at Pennsylvania State University and an author of the climate modeling study, said.

Climate policy opponents seized upon the global warming “pause” like a starving tiger being thrown red meat. Nevertheless, the old scientific method was able to drill down enough to dispel any false prior conclusions. Should a warming trend recommence after the new so called pause of 2016 as shown on Stefan’s chart (and it will looking at forecasts for 2019), more naysayers will need to drop off climate policy opposition or risk looking extremely foolish.

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Here is some more climate and weather news from Sunday:

(As usual, this will be a fluid post in which more information gets added during the day as it crosses my radar, crediting all who have put it on-line. Items will be archived on this site for posterity.)

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The Climate Guy

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