Judith Curry has a blog post (
archived here) in which she tries to justify this statement she made in her
written testimony to a recent
US Senate Committee Hearing.
Further, Arctic surface temperature anomalies in the 1930’s were as large as the recent temperature anomalies.
The Arctic and Antarctica
Judith made the statement in a section of
her testimony about sea ice in the Arctic and Antarctica. Judith included the following sentences in her written testimony, relating to Arctic sea ice and Antarctic sea ice. Unlike other science I've read and despite the gross differences between the two regions, Judith packaged the Arctic and Antarctica together. She wrote:
The increase in Antarctic sea ice is not understood and is not simulated correctly by climate models. Further, Arctic surface temperature anomalies in the 1930’s were as large as the recent temperature anomalies. Notwithstanding the simulations by climate models that reproduce the decline in Arctic sea ice, more convincing arguments regarding causes of sea ice variations requires understanding and ability to simulate sea ice variations in both hemispheres.
Her first sentence is more definite than the science I've read suggests. If she'd written "is not completely understood" or even "not well understood" it would be a more accurate representation of the state of science.
Her second sentence is most likely incorrect, as we'll see below. (I've emphasised that sentence in bold italics because it is going to be the main focus of this article.) But while we're here, let me just ask the question - if the Arctic was as warm in the 1930s as it is now, how is it there was so much more ice in the Arctic region back then than there is today? On land and sea.
Her third sentence is out of the blue and as far as I can make out, doesn't link directly to anything else in her testimony (except it fits her general theme of "scientists don't know nuffin' so forget-about-it").
The differences between the Arctic and Antarctica are vast. About the only similarity they share is they are both cold places with lots of ice. I'd be interested in what readers think about the "more convincing arguments" comment and just what Judith might mean by that. Sure it applies to Antarctica, but I can't see that the Arctic and Antarctica are linked as closely as Judith seems to be suggesting. I'm not arguing that what happens in Antarctica is divorced from the rest of the world or that it could not possibly have any impact on the Arctic. Merely that what happens in Antarctica is unlikely to have any greater impact on the Arctic than it has on anywhere else in the world. Similarly, what happens in the Arctic would not necessarily affect Antarctica any more than it would affect other regions in the world. And being in different hemispheres, they'd both arguably have less impact on each other rather than more.
So while it will be nice when all the different forces acting in the high latitudes of the southern hemisphere are better understood, I don't understand why Judith links Arctic sea ice with sea ice in the southern oceans.
However in this article I particularly want to discuss
the recent blog article of Judith's in which she tries to justify her statement and respond to
Tamino's criticism of Judith's writing:
Further, Arctic surface temperature anomalies in the 1930’s were as large as the recent temperature anomalies.
(Tamino has also
written a response, so I'll try to keep this short.)
Judith Curry is an expert on the climate of the Arctic
Now Judith introduced herself to the US Senate Committee as an expert on the climate of the Arctic. The first two sentences of her written testimony show how she presented herself:
I am Chair of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology. I have devoted 30 years to conducting research on topics including climate of the Arctic, the role of clouds and aerosols in the climate system, and the climate dynamics of extreme weather events.
So the first area of expertise she listed was that of the climate of the Arctic. So if anyone knows about the climate of the Arctic then she should. I am aware Judith has had quite a few papers about the Arctic published, her most recent being as co-author of one of
Marcia Wyatt's "stadium wave" papers I believe.
However, rather than cite any of her own work on the Arctic to support her statement that the Arctic was as hot in the 1930s as it is now, what Judith does in her blog article is select three passages from the
IPCC AR5 report in the section on Arctic sea ice (plus some other material). These are the sections she quotes - note they are not sequential in the IPCC report and are not adjacent to each other, though in her blog article Judith runs them all together as if they were a single segment. All are from Chapter 10, "Detection and Attribution of Climate Change: from Global to Regional".
The first segment is from page 10-27 of
AR5 WG1, in Section 10.3 Atmosphere and Surface:
Gillett et al. (2008b) detect anthropogenic influence on near-surface Arctic temperatures over land, with a consistent magnitude in simulations and observations. Wang et al. (2007) also find that observed Arctic warming is inconsistent with simulated internal variability. Both studies ascribe Arctic warmth in the 1930s and 1940s largely to internal variability. Shindell and Faluvegi (2009) infer a large contribution to both midcentury Arctic cooling and late century warming from aerosol forcing changes, with greenhouse gases the dominant driver of long-term warming, though they infer aerosol forcing changes from temperature changes using an inverse approach which may lead to some changes associated with internal variability being attributed to aerosol forcing. We therefore conclude that despite the uncertainties introduced by limited observational coverage, high internal variability, modelling uncertainties (Crook et al., 2011) and poorly understood local forcings, such as the effect of black carbon on snow, there is sufficiently strong evidence to conclude that it is likely that there has been an anthropogenic contribution to the very substantial warming in Arctic land surface temperatures over the past 50 years.
The above does not support or refute her contention that the Arctic was as warm in the 1930s as it is now. It's mainly blog padding.
The second segment is from page 10-43, except that Judith left out the first sentence of the paragraph, which I'll include as italics enclosed in square brackets.
[A question as recently as six years ago was whether the recent Arctic warming and sea ice loss was unique in the instrumental record and whether the observed trend would continue (Serreze et al., 2007).] Arctic temperature anomalies in the 1930s were apparently as large as those in the 1990s and 2000s. There is still considerable discussion of the ultimate causes of the warm temperature anomalies that occurred in the Arctic in the 1920s and 1930s (Ahlmann, 1948; Veryard, 1963; Hegerl et al., 2007a; Hegerl et al., 2007b). The early 20th century warm period, while reflected in the hemispheric average air temperature record (Brohan et al., 2006), did not appear consistently in the mid-latitudes nor on the Pacific side of the Arctic (Johannessen et al., 2004; Wood and Overland, 2010). Polyakov et al. (2003) argued that the Arctic air temperature records reflected a natural cycle of about 50–80 years. However, many authors (Bengtsson et al., 2004; Grant et al., 2009; Wood and Overland, 2010; Brönnimann et al., 2012) instead link the 1930s temperatures to internal variability in the North Atlantic atmospheric and ocean circulation as a single episode that was sustained by ocean and sea ice processes in the Arctic and north Atlantic. The Arctic wide temperature increases in the last decade contrast with the episodic regional increases in the early 20th century, suggesting that it is unlikely that recent increases are due to the same primary climate process as the early 20th century.
Judith bolded the second sentence in the above passage and omitted the first. A couple of people
have made much of this, and I agree that it is ambiguous. The second sentence could be read as a continuation of the first with the meaning: "
As recently as six years ago it appeared as if Arctic anomalies in the 1930s were as high as those of the 1990s and 2000s". Or it could be read as a standalone separate sentence, meaning that "
today it appears as if Arctic anomalies in the 1930s were as high as those of the 1990s and 2000s".
If you choose the second interpretation then that second sentence is the only bit of Judith's IPCC quotes that supports her contention that the Arctic was as warm in the 1930s as it is today. However it isn't consistent with anything else I've read in the IPCC report and I found no other statement of that nature in the report.
Not only that, but the very last sentence in the above passage should have been enough to alert Judith to the inconsistency - that the recent warming is Arctic-wide, unlike the warming in the early twentieth century, which was described as "episodic regional increases".
What is most concerning for people who might still harbour hope that Judith Curry has a bit of the scientist left in her, is that in talking about Arctic temperatures, Judith selected that particular passage and ignored conflicting passages.
The third passage Judith quoted is from page 10-42, still in the Arctic ice section of the report. The sentence in square brackets and italics was not quoted by Judith but is part of the same paragraph so I've included it for completeness.
Turning to model based attribution studies, Min et al. (2008b) compared the seasonal evolution of Arctic sea ice extent from observations with those simulated by multiple GCMs for 1953–2006. Comparing changes in both the amplitude and shape of the annual cycle of the sea ice extent reduces the chance of spurious detection due to coincidental agreement between the response to anthropogenic forcing and other factors, such as slow internal variability. They found that human influence on the sea ice extent changes has been robustly detected since the early 1990s. The anthropogenic signal is also detectable for individual months from May to December, suggesting that human influence, strongest in late summer, now also extends into colder seasons. Kay et al. (2011b), Jahn et al. (2012) and Schweiger et al. (2011) used the climate model (CCSM4) to investigate the influence of anthropogenic forcing on late 20th century and early 21st century Arctic sea ice extent and volume trends. On all timescales examined (2–50+ years), the most extreme negative extent trends observed in the late 20th century cannot be explained by modeled internal variability alone. Comparing trends from the CCSM4 ensemble to observed trends suggests that internal variability could account for approximately half of the observed 1979–2005 September Arctic sea ice extent loss. [Attribution of anthropogenic forcing is also shown by comparing September sea ice extent as projected by seven models from the set of CMIP5 models’ hindcasts to control runs without anthropogenic forcing (Figure 10.16a; Wang and Overland, 2009). The mean of sea ice extents in seven models’ ensemble members are below the level of their control runs by ~1995, similar to the result of Min et al. (2008b).]
The above should have been a signal to Judith to look further to make sure her claim of 1930s warming was correct. While it doesn't directly conflict with her claim, it states that recent warming is outside the bounds of natural variability, whereas the second passage she quoted above stated that the 1930s warming could be explained by natural variability. Anyone with half a brain would be asking themselves if that might mean that it was hotter recently than in the 1930s.
To sum up then, of all those passages, there is only one sentence that relates directly to Judith's claim. That's the sentence in the second passage that reads:
Arctic temperature anomalies in the 1930s were apparently as large as those in the 1990s and 2000s.
Thing is, that sentence is, as we've seen, ambiguous in the context of the paragraph. Not only that it is well and truly contradicted elsewhere in the IPCC report. I don't know who wrote it or why it slipped through when it could be read as conflicting with findings described elsewhere in the report. It could be an oversight. Yes, it could be a difference of opinion among scientists. If so then normally it would have been described as such in the report. So I'm thinking it's an ambiguous statement that no-one picked up on to remove the ambiguity. Maybe because the actual meaning was obvious to the IPCC authors and they didn't see any ambiguity.
To recap, Judith is attempting to justify her own statement to the US Senate Committee that:
Further, Arctic surface temperature anomalies in the 1930’s were as large as the recent temperature anomalies.
The above isn't an IPCC quote, it's Judith's own considered opinion as an expert on the Arctic climate. Like I said, in her blog justification she picked three passages from the IPCC section on Arctic sea ice, of which only one sentence of one passage could be argued as being supportive of her claim.
The evidence Judith Curry ignored
What Judith chose
not to quote was this passage on Arctic temperatures in Chapter 14, pp 14-39 and 14-40 (my bold italics):
The surface and lower troposphere in the Arctic and surrounding land areas show regional warming over the past three decades of about 1°C/decade—significantly greater than the global mean trend (Figures 2.22 and 2.25). According to temperature reconstructions, this signal is highly unusual: Temperatures averaged over the Arctic over the past few decades are significantly higher than any seen over the past 2000 years (Kaufman et al., 2009). Temperatures 11,000 years ago were greater than the 20th century mean, but this is likely a strongly-forced signal, since summer solar radiation was 9% greater than present (Miller et al.,
2010). Finally, warmer temperatures have been sustained in pan-Arctic land areas where a declining NAO over the past decade ought to have caused cooling (Semenov, 2007; Turner et al., 2007b).
Now there are two conflicting statements in different chapters of the IPCC report (assuming Judith's interpretation of the ambiguous sentence). The one a sentence that Judith quoted from Chapter 10, and the above paragraph from Chapter 14.
I looked further to see what else was in the IPCC report that Judith may have chosen to omit from her testimony. Here is a passage from page 5-33 of Chapter 5 of the IPCC report.
Since AR4, regional temperature reconstructions have been produced for the last 2 kyr (Figure 5.12; PAGES 2k Consortium, 2013). A recent multi-proxy 2000-year Arctic temperature reconstruction shows that temperatures during the first centuries were comparable or even higher than during the 20th century (Hanhijärvi et al., 2013; PAGES 2k Consortium, 2013). During the MCA, portions of the Arctic and sub-Arctic experienced periods warmer than any subsequent period, except for the most recent 50 years (Figure 5.12) (Kaufman et al., 2009; Kobashi et al., 2010; Vinther et al., 2010; Kobashi et al., 2011; Spielhagen et al., 2011). Tingley and Huybers (2013) provided a statistical analysis of northern high-latitude temperature reconstructions back to 1400 and found that recent extreme hot summers are unprecedented over this time span. Marine proxy records indicate anomalously high SSTs north of Iceland and the Norwegian Sea from 900 to 1300, followed by a generally colder period that ended in the early 20th century. Modern SSTs in this region may still be lower than the warmest intervals of the 900–1300 period (Cunningham et al., 2013).
Further north, in Fram Strait, modern SSTs from Atlantic Water appear warmer than those reconstructed from foraminifera for any prior period of the last 2000 years (Spielhagen et al., 2011). However, different results are obtained using dinocysts from the same sediment core (Bonnet et al. (2010) showing a cooling trend over the last 2000 years without a 20th century rise, and warmest intervals entered at years 100 and 600.
The words in the above passage do not by themselves directly refute Judith's one sentence claim that the Arctic was as hot in the 1930s as it is now. Nor does it lend any support to her claim. According to my reading of the above, the Arctic reconstruction suggests that recent temperatures in the Arctic are the highest they've been since the Medieval Climate Anomaly at least and probably the highest they've been in nearly 2000 years (at least). The "last fifty years" is not the 1930s but the period since the 1960s. We can leave aside the "portions of the Arctic" sentence because the issue is around the Arctic as a whole. The "recent extreme hot summers" is likely more relevant, but I haven't read the cited paper to see if it's "whole of Arctic".
Anyway, here is figure 5.12 which was referenced in the first paragraph of the above quote, which Judith chose to not divulge to the US Senate Committee:
 |
| Figure 5.12 IPCC AR5 WG1 [Arctic only] Regional temperature reconstructions, comparison with model simulations over the past millennium (950–2010). Temperature anomalies (thick black line), and uncertainty estimated provided by each individual reconstruction (grey envelope). Uncertainties: Arctic: 90% confidence bands. ...Simulations are separated into 2 groups: High solar forcing (red thick line), and weak solar forcing (blue thick line). For each model subgroup, uncertainty is shown as 1.645 times sigma level (light red and blue lines). For comparison with instrumental record, the CRUTEM4 dataset is shown (yellow line). Green bars in rectangles on top of each panel indicate the 30 warmest years in the 950–1250 period (left rectangle) and 1800–2010 period (right rectangle). All lines are smoothed by applying a 30 year moving average. ... Reconstructions: from PAGES 2k Consortium (2013). Models used: simulations with strong solar forcing (mostly pre-PMIP3 simulations): CCSM3 (1), CNRM-CM3.3 (1), CSM1.4 (1), CSIROMK3L-1-2 (3), ECHAM5/MPIOM (3), ECHO-G (1) IPSLCM4 (1), FGOALS-gl (1). Simulations with weak solar forcing (mostly PMIP3/CMIP5 simulations): BCC-csm1-1 (1), CCSM4 (1), CSIRO-MK3L-1-2 (1), GISS-E2-R (3, ensemble members 121, 124, 127), HadCM3 (1), MPI-ESM, ECHAM5/MPIOM (5), IPSL-CM5A-LR (1). In parenthesis are the number of simulations used for each model. All simulations are treated individually, in the timeseries as well as in the MCA–LIA bars. More information about forcings used in simulations and corresponding references are given in Table 5.A.1. |
Now given that Judith is a self-professed expert on the Arctic climate and has the publication history to prove it, there is no excuse in my mind for her to not divulge this to the US Senate Committee. She can't complain that she didn't know about it. It's in the very same document from which she selected her own quote.
Even if she disagreed with the latest research, she was being irresponsible at best, given that the above research is what is presented as being the current state of knowledge. Had Judith been acting as a scientist rather than a political stooge for the denialist party (Republicans), Judith would have presented the full spectrum of research and explained why she disputes the more recent findings.
In her blog article she didn't refer to the above either. She focused on material to support her claim (Wondering Willis style) while ignoring conflicting evidence. And it's especially damning that she put forward some guff from a blogger/denier (not a climate scientist) who thinks we're on the verge of an ice age and who can't read a simple chart of the Central England temperature (in which he ludicrously claims fame and expertise). (Another main bit of "evidence" Judith drew on in her blog article was some unpublished "work" one of her pet fake sceptics,
Tony "ice age cometh" Brown who barracks for the Central England team of deniers. So if you needed more evidence that she was searching for material to support her claim rather than reporting the science no matter what it showed, there you have it.)
Since I started this article, Tamino has written his
second blog article about the matter with more evidence against Judith. I might as well add this contribution to the mix since I've gone to the trouble of pulling it together.
The other reason I decided to go ahead and publish this is that Judith is flinching a bit and any bit of encouragement to act like a scientist could be worth it. I don't think Judith enjoys being shown up as just another ordinary fake sceptic blogger. I doubt she will change now, she's made her bed, chosen her path, whatever. Still, it's not too late for her to put aside her denier garb and don her white lab coat again, should she change her mind.
I'll leave it at that.
