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.}

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}.

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

• Huang et al. (2014) Extended Reconstructed Sea Surface Temperature version 4 (ERSST.v4), Part I. Upgrades and Intercomparisons, and
• Liu et al. (2014) Extended Reconstructed Sea Surface Temperature version 4 (ERSST.v4): Part II. Parametric and Structural Uncertainty Estimations.

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.

(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:

• Climate scientist Peter Thorne at the International Surface Temperature Initiative.
• Gavin Schmidt (Director of NASA’s Goddard Institute of Space Sciences; bio here) at RealClimate.

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“.

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).

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:

• Scientists explore causes of the pause in warming, perhaps the most important research of the decade., with abstracts and links to 37 articles describing 12 theories about causes of the pause.
• One of the most important questions we face: when will the pause in global warming end? with abstracts and links to 15 articles giving predictions from very soon to several decades from now.