by Judith Curry
A new blockbuster paper published today by NOAA:
These results do not support the notion of a “slowdown” in the increase of global surface temperature.
Color me ‘unconvinced.’
Possible artifacts of data biases in the recent global surface warming hiatus
Thomas R. Karl, Anthony Arguez, Boyin Huang, Jay H. Lawrimore, James R. McMahon, Matthew J. Menne, Thomas C. Peterson, Russell S. Vose, Huai-Min Zhang
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.
The paper has just been published in Science Express [link] (apparently will be open access).
Here is the main summary diagram from the paper:
JC’s initial reactions
I received this several days ago, from an (international) journalist asking for comments, my quick initial reactions provided below:
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 – ARGO buoys and 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 http://www.metoffice.gov.uk/hadobs/hadsst3/uncertainty.html. 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, 7, 83-84.
Relevant text:
Gap filling in the Arctic is complicated by the presence of land, open water and temporally varying sea ice extent, because each surface type has a distinctly different amplitude and phasing of the annual cycle of surface temperature. Notably, the surface temperature of sea ice remains flat during the sea ice melt period roughly between June and September, whereas land surface warming peaks around July 1. Hence using land temperatures to infer ocean or sea ice temperatures can incur significant biases.
With regards to uncertainty, in their ‘warmest year’ announcement last January, NOAA cited an error margin in the global average surface temperature anomaly of 0.09oC. The adjustments to the global average surface temperature anomaly is within the error margin, but the large magnitude of the adjustments further support a larger error margin. But they now cite a substantially greater trend for the period 1998-2014, that is now statistically greater than zero at the 90% confidence level.
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.
CATO comments
Pat Michaels sent me these comments, which will be posted at the CATO web site:
IS THERE NO “HIATUS” IN GLOBAL WARMING AFTER ALL?
Patrick J. Michaels, Richard S. Lindzen, Paul C. Knappenberger
A new paper, from Thomas Karl and several co-authors[1], that removes the “hiatus” in global warming, will doubtless receive much attention in both scientific and policy circles. As with many scientific publications, Karl et al. prompts many serious scientific questions.
While this will be heralded as an important finding, the main claim[2] that it uncovers a significant recent warming trend is certainly dubious. The significance level (.10) is hardly normative and the use of it certainly will prompt many readers to question the reasoning behind the use of such a lax standard.
The treatment of the buoy sea-surface temperature (SST) data was guaranteed to put a warming trend in recent data. They were adjusted upwards 0.12°C to make them “homogeneous” with the longer-running temperature records taken from engine intake channels in marine vessels. As has been acknowledged by numerous scientists, the engine intake data are clearly contaminated by heat conduction from the structure, and they were never intended for scientific use. On the other hand, environmental monitoring is the specific purpose for the buoys. Adjusting good data upwards to match bad data seems questionable, and the fact that the buoy network becomes increasingly dense in the last two decades means that this adjustment must put a warming trend in the data.
The extension of high-latitude arctic land data over the Arctic Ocean is also questionable. Much of the Arctic Ocean is ice-covered even in high summer, so that the surface temperature must remain near freezing. Extending land data out into the ocean will obviously induce substantially exaggerated temperatures.
Additionally, there multiple measures of bulk lower atmosphere temperature that are made independently from surface measurements and which indicate the existence of a “hiatus”[3]. 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.
Instead, it would seem more logical to seriously question the Karl et al. result in light of the fact that, compared to those bulk temperatures, it is an outlier, showing a recent warming trend that is not in these other global records.
[1] Karl, T. R., et al., Possible artifacts of data biases in the recent global surface warming hiatus. Scienceexpress, embargoed until 1400 EDT June 4, 2015.
[2] “It is also noteworthy that the new global trends are statistically significant and positive at the 0.10 significance level for 1998-2012…”
[3] Both the UAH and RSS satellite records are now in their 21st year without a significant trend, for example
GWPF comments
Received via email from GWPF:
Key pitfalls of the paper:
- The authors have produced adjustments that are at odds with other all other surface temperature datasets, as well as those compiled via satellite.
- They do not include any data from the Argo array that is the world’s best coherent data set on ocean temperatures.
- Adjustments are largely to sea surface temperatures (SST) and appear to align ship measurements of SST with night marine air temperature (NMAT) estimates, which have their own data bias problems.
- The extend of the largest SST adjustment made over the hiatus period, supposedly to reflect a continuing change in ship observations (from buckets to engine intake thermometers) is not justified by any evidence as to the magnitude of the appropriate adjustment, which appears to be far smaller.
1. They make 11 changes (not all are explained) producing the ERSSTv4 Sea Surface Temperature (SST) dataset that includes new estimates for the different way SSTs are measured from ships (intake or buckets). They also add 0.12°C to each buoy to bring their measurements in line with those taken from ships. These issues have been raised before by the UK Met Office when compiling their HadSST3 ocean surface temperature dataset, see, ‘A review of uncertainty in in situ measurements and data sets of sea surface temperature’
2. The greatest changes are made since 1998, which is interesting because this is when we have the highest quality of data and global coverage using several methods. Only this analysis finds any increase in global annual average surface temperature over this “hiatus” period. The authors have produced a dataset that is at odds with other surface temperature datasets, as well as those compiled via satellite.
3. The authors start their trend estimates in 1998 and 2000. This has long been considered unwise as 1998 is a very strong El Nino year and 1999-2000 is a much cooler La Nina period. The difference between them distorts their trend estimates. For example, their 1998-2014 trend is 0.106+/- 0.058°C per decade. Starting two years later (during La Nina influenced years) yields a trend of 0.116 +/- 0.067°C per decade as one would expect from starting at a lower temperature. Ignoring these caveats the authors say their analysis produces twice as much warming for 1998-2014 than earlier estimates. Their conclusion is, ironically, based on inbuilt biases in their analysis.
Their Fig 1 shows that when using their updates it is only with the use of these inappropriate start and end points that the “hiatus” is reduced.
4. Even with the 11 changes to their SST database and the problem of start and end dates the authors admit that the statistical significance of their results is only significant at the 0.10 level, and in some cases not even that.
“I believe their estimates of the error in their decadal trend figures are far too small. They quote the error in a 15-year period to a precision of one thousandth of a degree C. In their report the authors admit that their error analysis is not definitive and that looking at them another way invalidates their trend conclusions,” said Dr David Whitehouse, science editor of the GWPF.
5. Note that trends that include 2014 and 2015 must be treated with caution due to a recently persistent very warm feature in the NE Pacific that is affecting global SST estimates.
6. In addition, they do not include any data from the Argo array that is our best coherent data set on ocean temperatures. The authors state this is because Argo temperature data is not surface data. However, ship-derived temperatures can be from as much as 15 m below the surface. The Argo array samples 5 m below the top of the ocean. From 2004 to 2013 it shows considerable variation and little trend. The non-ARGO data aptly demonstrates the problem of starting trend analysis in 1998 or 2000.
Source: ‘Unabated planetary warming and its ocean structure since 2006’ Nature Climate Change, 2 February 2015. Black line: 5 m optimally interpolated (OI) ARGO; red lines: NOAA OI SST v2
7. Their conclusions are also at odds with satellite data that shows no trend in the past 16-years or so.
Source: http://nsstc.uah.edu/climate/index.html and http://www.remss.com/research/climate
8. Extending a change in ship observations (from buckets to engine intake thermometers) to the present time had the largest impact on the SST adjustments over the hiatus period, per Karl et al 2015:
“Second, there was a large change in ship observations (i.e., from buckets to engine intake thermometers) that peaked immediately prior to World War II. The previous version of ERSST assumed that no ship corrections were necessary after this time, but recently improved metadata (18) reveal that some ships continued to take bucket observations even up to the present day. Therefore, one of the improvements to ERSST version 4 is extending the ship-bias correction to the present, based on information derived from comparisons with night marine air temperatures. Of the 11 improvements in ERSST version 4 (13), the continuation of the ship correction had the largest impact on trends for the 2000-2014 time period, accounting for 0.030°C of the 0.064°C trend difference with version 3b.”
Ref (18) is a 2011 paper by Kennedy et al. It states (paragraph 3.1) “Dating the switchover from uninsulated canvas buckets to insulated rubber buckets is problematic as it is not clear how quickly the practice of using insulated buckets was adopted. … Based on the literature reviewed here, the start of the general transition is likely to have occurred between 1954 and 1957 and the end between 1970 and 1980.”
A 2010 review article “Effects of instrumentation changes on SST measured in situ” by Kent, Kennedy, Berry and Smith states that “Models of corrections for wooden and uninsulated canvas buckets show the adjustments to be five to six times greater for the canvas buckets.”
So post 1980 adjustments to bucket measurements should be very small (under 0.1 C) Moreover, by 2000 ship measurements were a minority of total measurements and all types of bucket were a small proportion of ship measurements (see figs 2 and 3 of Kent et al. 2010). These facts imply that post 2000 adjustments warranted by use in some ships of bucket measurements should be negligible.
“The justification given for the change that had the largest impact on trends for the 2000-2014 time period – continuing to adjust ship SST measurements by reference to night marine air temperature (NMAT) data, ‘which have their own particular pervasive systematic errors’ (Kennedy 2014) – i.e. that some ships still continue to take bucket observations, appears to support only a very small adjustment,” said Nic Lewis, an independent climate scientist.
In summary
This is a highly speculative and slight paper that produces a statistically marginal result by cherry-picking time intervals, resulting in a global temperature graph that is at odds with those produced by the UK Met Office and NASA.
Caution and suitable caveats should be used in using this paper as evidence that the global annual average surface temperature “hiatus” of the past 18 years has been explained.
JC summary
I am posting this at 2 p.m. ET (when the press embargo is released). I will provide all the relevant links as soon as available, and will update with links to the forthcoming articles from the MSM; I am particularly interested in what ‘consensus’ supporting scientists have to say about this.
UPDATES:
Post at WUWT by Anthony Watts and Bob Tisdale [link]
From Carbon Brief:
Prof Sir Brian Hoskins, chair of the Grantham Institute at Imperial College London, says:
“[I]t had been thought that the reduction in surface warming must be due to natural variation in the heat exchanged between the atmosphere and ocean. Now it appears that any such exchange of heat between the atmosphere and ocean has not been large enough to obscure the global warming trend.”
But we shouldn’t dismiss the presence of a “slowdown” in surface warming just yet, warns Osborn. He says:
“There are other datasets that still support a slowdown over some recent period of time, and there are intriguing geographical patterns such as cooling in large parts of the Pacific Ocean that were used to support explanations for the warming slowdown.”
Neither should scientists stop seeking to understand the role of natural decadal variability in influencing short-term trends in climate, Osborn says. Dr Peter Stott, head of climate monitoring and attribution at the Met Office Hadley Centre, echoes this point, saying:
“[N]atural variability in the climate system or other external factors have still had an influence and it’s important we continue research to fully understand all the processes at work.”
On the whole, scientists seem to welcome the new study in terms of its contribution to fine-tuning the global surface temperature record. But the so-called “hiatus” – its causes, consequences and even its very existence – is a multi-faceted topic. Forster predicts:
“I still don’t think this study will be the last word on this complex subject.”
Post from the International Surface Temperature Initiative [link]
Doug MacNeal’s take [link].
Seth Borenstein from the AP:
Several outside scientists contacted by The Associated Press said the new and previous adjustments are sound. Kevin Trenberth, climate analysis chief at the National Center for Atmospheric Research, said the new work was “good and careful analysis” but only confirms what most scientists already knew, that there was no such hiatus.
“NOAA is confirming what we have been saying for some time that the ‘hiatus’ in global warming is spurious,” Berkeley team chief and physicist Richard Muller said in an email. Muller said global warming continues but in “many fits and spurts.”
John Christy of the University of Alabama Huntsville, one of the minority of scientists who dispute the magnitude of global warming, said the Karl paper “doesn’t make sense” because satellite data show little recent warming. “You must conclude the data were adjusted to get this result” of no warming pause, Christy wrote in an email. “Were the adjustments proper? I don’t know at this point.”
From Mashable:
Scientists who have investigated the warming hiatus or are otherwise involved in assessing climate change on various timescales told Mashable that the study’s key shortcoming is that it does what mainstream climate scientists have long criticized the climate contrarians, often now referred to as “climate denialists,” of doing: cherry-picking start and end dates to arrive at a particular conclusion.
Gerald Meehl, a climate researcher at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, told Mashable in an email that while he finds the new study laudable for improving temperature measurements, there are flaws in how the researchers interpreted the data. For example, Meehl says there is still a lower warming trend from 1998 to 2012 compared to the previous base period of 1950 to 1999, “… Thus there is still a hiatus defined in that way.”
Meehl says that adding two years to the time period by including 2013 and then 2014, which was a record warm year, makes the warming trend appear to be 38% larger than previous studies that did not include those two years.
“My conclusion is that even with the new data adjustments, there still was a nominal hiatus period that lasted until 2013 with a lower rate of global warming than the warming rate of the last 50 years of the 20th century,” Meehl says, “and a factor of two slower warming than the previous 20 years from the 1970s to 1990s.”
Lisa Goddard, director of the International Research Institute for Climate and Society (IRI) at Columbia University, told Mashable that the study does not support the conclusion that global warming didn’t slow down for a relatively short time period.
“It is clear that Karl et al. have put a lot of careful work into updating these global products,” Goddard said in an email. “However, they go too far when they conclude that there was no decadal-scale slowdown in the rate of warming globally. “However, they go too far when they conclude that there was no decadal-scale slowdown in the rate of warming globally. This argument seems to rely on choosing the right period — such as including the recent record breaking 2014.”
Another senior climate researcher, Kevin Trenberth of NCAR, says the hiatus depends on your definition of the term. To him, global warming never stopped, as climate skeptics argue, because most of the extra heat from manmade greenhouse gases such as carbon dioxide was redirected deep into the oceans during the 1998 to 2012 period. However, surface temperatures did warm more slowly during this time.
“I think the article does emphasize that the kind of variation is now much more within the realm of expectations from natural variability, but it is a bit misleading in trying to say there is no hiatus,” he said in an email conversation.
Michael Mann, the director of the Earth System Science Center at Penn State University, says the study helps drive home the point that “global warming continues unabated as we continue to burn fossil fuels and warm
the planet.”
The new study reveals yet again that surface temperature data has many flaws, says Peter Thorne, a climate researcher at Maynooth University in Ireland. In an interview, Thorne said critics of climate science are incorrect in charging that global warming is an artifact of urban heat islands and other influences on thermometers, but at the same time, our approach to taking the Earth’s temperature needs to be rethought.
Thorne says more investments should go toward establishing redundant, carefully calibrated temperature observing networks where data is currently sparse, such as the Arctic, much of Africa and especially the oceans.
““The uncertainty in the marine records is far greater than in the land records,” he said.
“If we put enough good quality, traceable, redundant observations around the globe we can make sense of all the other observations that aren’t so good,” he said. “There is no need to bequeath onto researchers in 50 years time a similar mess.”
Filed under: Data and observations