Won't cha let me take you on a sea cruise? (It's about the hiatus.)
Won't cha let me take you on a sea cruise?
I have a friend going a sea cruise, and he’ll be talking about climate change. He is expecting questions about the warming hiatus. Now, I don’t know what my readers think about scientists on vacation, but this sounds about right. I promised a summary of what has happened to the hiatus distraction since the last cruise.
I did a summary almost two years ago called, The Whole Silly Warming Pause, Warming Hiatus Thing. It’s, still, a pretty good summary. I also mentioned a couple of recent papers in passing last summer, but I was writing more about how science communications influence research.
For those who came in late: The warming hiatus was manufactured and named in the press, with climate-science skeptics extracting a simple figure designed for communication, shredding that figure’s inability to represent the complexity of climate science, and posing those fragments of shredded simplicity as deficiencies of knowledge and, indeed, as flaws of character and integrity. The scientific community has responded to those questions, answering them with increasingly more quantitative and accurate answers. There is now a Warming Hiatus Wikipedia article.
The most important scientific fact (a word I do not often use) about the warming hiatus is that the heat accumulating in the Earth’s climate does not all go into heating the atmosphere. The majority of the heat actually goes into the ocean and melting ice. Therefore, the global surface air temperature is influenced not only by heat absorption, but also heat exchanges, especially, with the ocean. (My piece in The Conversation) The exchange of heat with the ocean is why it was so easy to predict that 2015 would be a record warm year as the eastern Pacific Ocean warmed with El Niño. (See also, Recent hiatus caused by decadal shift in Indo-Pacific heating, by Nieves and others.)
Exchanges with the ocean do not explain all of the bumps and wiggles in the atmospheric temperature record. The bumps and wiggles motivate scientific curiosity, and they are also fodder for the public discourse. Another of the facts of climate science is that many of the observations used in climate science were not originally collected with climate in mind. Sometimes the data were collected for weather forecasting, and sometimes the data were collected for other reasons, like military, industrial, and transportation applications. Climate data requires, especially, exquisite attention to how the data behaves with time. For example, thermometer technology changes over time; thermometer manufacturers change over time – and so it goes. Therefore, one of activities of scientists is making Climate Data Records. Of course this long-standing practice of good science can appear to the skeptic as manipulation of data - a point that is rarely loss in the public forum.
The first paper I mention, Karl and others, Possible artifacts of data biases in the recent global surface warming hiatus, looks at the quality of data, improved data coverage, and the reconciliation of biases. (With luck, full paper) This is a short paper, and much of the discussion is related to sea surface temperatures. It has been known for some time that there was inhomogeneity in the sea surface temperature data set. An especially interesting time was during and after World War II, when there were changes in how the sea surface temperature was being measured, as the balance of observations changed between the U.S. and British navies. In neither case, I assert, were the sailors thinking “climate change.” Here are some links to discussions of the sea surface data: Skeptical Science, HadSST3: A detailed look // Nature Climate Change, Post-World War II cooling a mirage // Huang, J Climate, Extended Reconstructed Sea Surface Temperature Version 4 (ERSST.v4). Part I: Upgrades and Intercomparisons.
Karl and others determine significant impacts on the temperature record following 1950 with changes related to “new time-dependent bias corrections.” They state: “These results do not support the notion of a “slowdown” in the increase of global surface temperature.” There is a nice analysis of the Karl and others paper provided by NASA’s Earth Observatory, Parsing the Details of the New Warming “Hiatus” Study (Adam Voiland).
In an approach that focuses on more sophisticated and robust statistical analysis, Rajaratnam and others, Debunking the climate hiatus, conclude “We find compelling evidence that recent claims of a “hiatus” in global warming lack sound scientific basis. Our analysis reveals that there is no hiatus in the increase in the global mean temperature, no statistically significant difference in trends, no stalling of the global mean temperature, and no change in year-to-year temperature increases.” I like this paper a lot. It takes on a series of hypotheses and investigates if there are measureable, statistically significant reductions in warming over the length of the record. The hypotheses are:
Hypothesis I: hiatus in temperature trend during 1998–2013;
Hypothesis II: difference in temperature trends;
Hypothesis III: hiatus in the mean global temperature;
Hypothesis IV: difference in year-to-year temperature changes
They also analyze both the corrected and the uncorrected data sets discussed in the Karl and others paper above. Though the data corrections are important, under the scrutiny of this statistical analysis the conclusions do not change. That is, the corrected data are not needed to cast out the hypothesis of a warming hiatus. (Sanford press release on paper) Ultimately, the Rajaratnam and others paper takes on the tactic of extracting a short time series following the 1998 El Niño and manufacturing the hiatus as challenge to the substance and credibility of the climate change science.
Finally, I mention an interesting, perhaps, meta-analysis (looks at many studies). In their paper Lewandowsky and others, On the definition and identifiability of the alleged “hiatus” in global warming, state, “ … we show that even putting aside possible artifacts in the temperature record, there is no substantive evidence for a “pause” or “hiatus” in warming. We suggest that the use of those terms is therefore inaccurate. Because this conclusion appears to contradict the IPCC’s explicit endorsement of the “hiatus”, it is important to differentiate between the different ways in which the term “pause” or “hiatus” has been motivated and used in the recent climatological literature.” This paper, again, takes on the tactic of isolated short time series used in the original manufacturing of the hiatus; they find that in virtually any short time period something that could be construed and amplified as a hiatus can be identified.
So … the manufacturing of the warming hiatus and the way the scientific community has embraced it has, once again, strengthened the scientific foundation of climate change. The studies I mentioned, above, are only a subset of the papers that have emerged to explain the bumps and wiggles in the global-average, surface air temperature record. These studies continue to describe and, in some cases, reduce the uncertainty in the temperature record and the trends. If you float around the web, you will find some who continue to maintain there are large uncertainties in the temperature observations and their interpretations. There is little evidence, to me, that there is anything that might be viewed as seriously challenging the conclusions that the Earth is warming, ice is melting, sea level is rising, and the weather is changing. And, once again, I remind ourselves that uncertainty can always be used as a political tactic of disruption.
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I'm a professor at U Michigan and lead a course on climate change problem solving. These articles often come from and contribute to the course.
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