Science & Nature

The Pause in global warming has ended. Now see the rest of the story.

Summary: A new paper in Science grapples with pause in atmospheric warming, one of the frontiers in climate science. I expect that the news media will give it mega-coverage, total applause (papers that challenge the paradigm are ignored). Here are comments by climate scientists giving the vital context that few journalists will mention. The important thing to know, a secret to journalists, is that laypeople should focus on the trend of the literature — or summaries like those of the IPCC — rather than the cherry-picked papers highlighted by activists on both sides. {2nd of 2 posts today.}

Community Climate System Model

Community Climate System Model

A major new report just published in Science by a team of NOAA climatologists will roil the debate about the vital subject: “Possible artifacts of data biases in the recent global surface warming hiatus” by Thomas R. Karl et al. The timing is significant, one of a series of papers appearing before November’s United Nations Climate Change Conference in Paris.  Abstract…

Much study has been devoted to the possible causes of an apparent decrease in the upward trend of global surface temperatures since 1998, a phenomenon that has been dubbed the global warming “hiatus.” Here we present an updated global surface temperature analysis that reveals that global trends are higher than reported by the IPCC, especially in recent decades, and that the central estimate for the rate of warming during the first 15 years of the 21st century is at least as great as the last half of the 20th century. These results do not support the notion of a “slowdown” in the increase of global surface temperature.

Excerpts from the paper.

The Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report concluded that the global surface temperature “has shown a much smaller increasing linear trend over the past 15 years [1998-2012] than over the past 30 to 60 years.” The more recent trend was “estimated to be around one-third to one-half of the trend over 1951-2012.” The apparent slowdown was termed a “hiatus,” and inspired a suite of physical explanations for its cause, including changes in radiative forcing, deep ocean heat up-take, and atmospheric circulation changes.

While these analyses and theories have considerable merit in helping to understand the global climate system, other important aspects of the “hiatus” related to observational biases in global surface temperature data have not received similar attention. In particular, residual data biases in the modern era could well have muted recent warming, and as stated by IPCC, the trend period itself was short and commenced with a strong El Niño in 1998. Given recent improvements in the observed record and additional years of global data (including a record-warm 2014), we re-examine the observational evidence related to a “hiatus” in recent global surface warming.

… It is also noteworthy that the new global trends are statistically significant and positive at the 0.10 significance level for 1998–2012 {i.e., weakly significant}.

NOAA logo

Bob Tisdale points to the papers this builds on, especially …

Some comments about the paper

This paper is significant as it (and the above 2) disagrees with much (most?) of the previous work about these issues. Here is an excellent summary of the literature. We can expect journalists to report this paper’s conclusions without a total lack of context about this.

(1)  Doug McNeall (climate scientist, UK Met Office; bio here) at his website

The changes to the global mean temperature record are, in the grand scheme of things, really quite small. … My colleague Chris Roberts points out that the necessary comparison is with the expected warming (and associated distribution) from the models, not from the somewhat arbitrary threshold of “zero” warming. Here’s a comparison from our paper on the future of the hiatus, from earlier this year:  “Quantifying the likelihood of a continued hiatus in global warming“, Nature Climate Change, in press.

C D Roberts et al, Nature Climate Change

(2)  Ryan Maue (climate scientist at WeatherBELL; bio here) at Climate Etc

… a prime reason for using the surface station + in-situ SST {sea surface temperature} network is to compute in anomaly space a very long time series e.g. 1880-present of temperatures. We can show a gradual warming trend over the past century that occurs in steps.

… Since 1979, we have global satellite coverage from a multitude of sensors that measure (in)directly many aspects of the climate system. Numerical weather prediction techniques like 4D-Var used by the best weather models (ECMWF, UKMET) produce an analysis of the atmosphere-ocean system every day incorporation so much data from many sources that imo it’s one of humanity’s remarkable achievements.

For the past several decades, I contend that surface-station datasets are insufficient and (perhaps) not well suited to describe the exact global temperature. The methods used by NOAA/NASA/BEST are akin to the quality control procedures required by every NWP data assimilation scheme to initialize the analysis prior to running a weather forecast.

(3)  Climate scientists Patrick J. Michaels and Richard S. Lindzen at CATO

multiple measures of bulk lower atmosphere temperature that are made independently from surface measurements and which indicate the existence of a “hiatus”. If the Karl et al., result were in fact robust, it could only mean that the disparity between surface and midtropospheric temperatures is even larger that previously noted. Getting the vertical distribution of temperature wrong invalidates virtually every forecast of sensible weather made by a climate model, as much of that weather (including rainfall) is determined in large part by the vertical structure of the atmosphere.

{red emphasis added}

(4)  Judith Curry (Prof Atmospheric Science, GA Inst Tech; bio here) at Climate Etc

The greatest changes in the new NOAA surface temperature analysis is to the ocean temperatures since 1998.  This seems rather ironic, since this is the period where there is the greatest coverage of data with the highest quality of measurements – satellites don’t show a warming trend.  Nevertheless, the NOAA team finds a substantial increase in the ocean surface temperature anomaly trend since 1998.

In my opinion, the gold standard dataset for global ocean surface temperatures is the UK dataset, HadSST3.  A review of the uncertainties is given in this paper by John Kennedy.  Note, the UK group has dealt with the same issues raised by the NOAA team.  I personally see no reason to the use the NOAA ERSST dataset, I do not see any evidence that the NOAA group has done anywhere near as careful a job as the UK group in processing the ocean temperatures.

I am also unconvinced by NOAA’s gap filling in the Arctic, and in my opinion this introduces substantial error into their analysis.  I addressed the issue of gap filling in the Arctic in this recent publication:  Curry JA, 2014:  Climate science:  Uncertain temperature trends. Nature Geoscience.

… My bottom line assessment is this. I think that uncertainties in global surface temperature anomalies is substantially understated. The surface temperature data sets that I have confidence in are the UK group and also Berkeley Earth. This short paper in Science is not adequate to explain and explore the very large changes that have been made to the NOAA data set. The global surface temperature datasets are clearly a moving target.

So while I’m sure this latest analysis from NOAA will be regarded as politically useful for the Obama administration, I don’t regard it as a particularly useful contribution to our scientific understanding of what is going on.

(5)  Chris Merchant (Prof in Ocean & Earth Observation, U of Reading; bio here) at Sea Surface Temperature for Climate

When talking about a revision of temperatures that is so subtle, it is prudent to be cautious. Karl et al. recognise this in the title of their paper “Possible artifacts of data biases in the recent global surface warming hiatus” (my emphasis).

… Karl et al.’s “new” value of SST change over this interval therefore fits pretty well with our independent [3] satellite data. These data featured in IPCC AR5. (They also agree well with the Hadley Centre in situ ensemble in the same figure.)

So, how new Karl et al.’s result is depends on what data you previously paid attention to. And I would still describe 0.06°C/decade as a slowdown compared to the 1980s and 1990s.  {Hat tip on this to Climate Etc.}

Other remarks about this paper

By scientists:

At Mashable Andrew Freedman explains this for laypeople (without mention of the opposite results from the satellite network, which might confuse the narrative): “Global warming slowdown never happened, federal study says“.

Stand back I'm trying science.

My Conclusions

Scientists will evaluate this contribution to the debate in the coming months. Activists and their journalist allies will misrepresent this paper as definitive, instead of additional to the large and so-far contradictory literature about the pause. Eventual a consensus will form.

However, if successful predictions are the gold standard of science theory, post-hoc adjustments that support theory –such as those in this paper — are the brass standard. While they play a useful role, they’re unlikely to change the balance of opinion among laypeople concerned about the public policy implications of these trends.

What if these adjustments are accepted, a tiny change to the recent trend that removes the pause from the record? The focus of the debate might shift from the trend of surface temperatures to the large and growing divergences between …

  • forecast of models and actual temperatures, and
  • the difference between warming measured by networks of surface stations and lack of warming in satellite measurements of the lower atmosphere.

Each of these fundamentally challenge the climate science paradigm. Such a shift in focus might be a good result, since they are possible to resolve, whereas the measurement difficulties in historical surface record are difficult or perhaps impossible to resolve (too many instruments over time, few of which designed for climate science, and often poorly documented).

Postcards from the frontier of science

For More Information

To learn more about the state of climate change see The Rightful Place of Science: Disasters and Climate Change by Roger Pielke Jr. (Prof of Environmental Studies at U of CO-Boulder, and Director of their Center for Science and Technology Policy Research).

Most of these references are from Judith Curry’s post at Climate Etc. If you liked this post, like us on Facebook and follow us on Twitter. See these Reference Pages for other posts about climate on the FM sites:  The keys to understanding climate change and My posts about climate change. Also, see these posts about the pause:




6 replies »

  1. One thing that strikes me is that the significance level of their results is only 0.10 . Maybe this is acceptable in this field but even tenuous results that were barely publishable in my old area in astronomy were 2.5 sigma (about 0.02 significance). And trillions of dollars are riding on this.

    Liked by 2 people

    • Socialbill,

      I agree. Looking at this from the bleachers, I found the attention to this odd. It contradicts much of the literature, makes quite small adjustments with low level of statistical significance, gives astonishingly small error bars — and continues climate sciences focus ignoring the more serious divergences.

      Despite all that, my guess is that this will be played up in the news like the Second Coming.

      Liked by 1 person

  2. The New York Times spins the climate science news

    About the new NOAA paper: “Global Warming ‘Hiatus’ Challenged by NOAA Research” by Justin Gillis in the NYT.

    … The change prompted accusations on Thursday from some climate-change denialists that the agency was trying to wave a magic wand and make inconvenient data go away. Mainstream climate scientists not involved in the NOAA research rejected that charge, saying it was essential that agencies like NOAA try to deal with known problems in their data records.
    At the same time, senior climate scientists at other agencies were in no hurry to embrace NOAA’s specific adjustments. Several of them said it would take months of discussion in the scientific community to understand the data corrections and come to a consensus about whether to adopt them broadly.

    “What you have is a reasonable effort to deal with known biases, and obviously there is some uncertainty in how you do that,” said Gavin A. Schmidt, who heads a NASA climate research unit in New York that deals with similar issues.

    … Scientists like Dr. Meehl never accepted the notion, put forward by some climate contrarians, that the slowdown disproved the idea that global warming poses long-term risks. But they said they believe it is real and demands an explanation.

    The story raises an important question. Did NASA’s weather satellite fall from the sky? NASA pays Remote Sensing Systems (RSS) and the University at Alabama – Huntsville (UAH) to produce data on global temperature going back to 1979. Neither shows warming since roughly 1998-2000, but there seems to be a black-out on this fact in the major media. Endless articles about “the Warmist Year” and the end of the pause — but few if no mentions of the satellite data. This NYT article carries on that tradition.


  3. Dr. Bouldin took a look at the data:

    The rate {temperature trend} from 1998 to 2012 is given as 0.086. This means the rate from 1951 to 1997, which is what you need for the proper comparison but which is not reported, must therefore be … 0.133. So that’s 0.133 vs 0.086, which is a ratio of about 1.55.

    If one picks the year 2000 as the demarcation point between the two periods, then it’s a little trickier because Karl et al don’t actually give an estimated rate from 2000 to 2012. But one can estimate it by assuming the rate difference between 1998 to 2014, and 2000 to 2014, both of which they do give, is a decent approximation of the difference between 1998-2012 and 2000-2012. When I do so, I get a ratio of warming rates between the two periods (1951-1999 and 2000-2012) that’s very similar: 1.47.

    Taking the inverses, the rate of warming between the slowdown period and the pre-slowdown period, is about 2/3. Given the large number of data points (grid boxes) that make up each year’s mean value, it has to be essentially certain that, according to these data, there has in fact been a very highly statistically significant difference in warming rates between these two periods, regardless of whether you use 1998 or 2000 as the breakpoint year. …

    Editor’s note: From Dr. Bouldin’s About Page: “I have … a PhD in Plant Biology from the UC-Davis. … I’m primarily a forest ecologist.”

    Liked by 1 person

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