Getting rid of the spurious blips - another look at global sea surface temperatures

Kevin Cowtan | Source: U York

Once again, Kevin Cowtan has brought his skills to climate science, working with Robert Rohde and Zeke Hausfather. They decided to explore those pesky ups and downs in the temperature record, which a lot of people (scientists mostly) have expressed concerns about. This new paper is largely addressing bucket bias in sea surface temperature and is very detailed. Taken with his other work on temperature records, this has to cement Kevin Cowtan's place among the "serious climate nerds" (h/t ykw!)

A hybrid check on sea surface temperature bias corrections

The authors analysed sea surface temperature, the main source of the temperature blips, from a new perspective. Their analysis can be seen mainly as a check of the bias corrections used in other sea surface temperature records. Instead of reanalysing data from ships and buoys, they compared weather stations on the coast and on islands with the measurements taken on ships when they passed close to the coast. They subjected this to further analysis and called the result a hybrid SST (sea surface temperature).

I can only imagine how much work this must have entailed. There are hints in the paper. Not only did they get the temperature records from land and nearby sea, they made adjustments in their analysis to compensate for the fact that with global warming, the land surface is warming faster than the sea surface, plus more.

They used their results to assess the bias correction that needs to be made when the sources for sea surface temperature changed, such as from buckets to engine intake, and to buoys (see below). The end result was a different check on sea surface temperatures and additional evidence that:

• Some of the odd blips in the temperature records were not what actually happened - particularly the upward WWII blip and the drop down around 1910
• The NOAA sea surface temperature record from 1997 onwards is probably closest to reality. On the other hand, the Cowtan17 analysis indicates ERSST v4 is too warm in the earliest years (1860 to 1900 or so) and too cool in the early 20th century (1910 to late 1930s).
• Climate models reflect reality even more closely than previous records suggest. 

There's an excellent article on Kevin Cowtan's website which explains the research, and accompanying provisos. The paper and supporting information contain a lot more detail, including all the ifs and buts and maybes. Co-author Zeke Hausfather has a  Twitter thread about the paper, too.

Challenges in the historical record of sea surface temperature

The authors begin by pointing out that getting a record of sea surface temperature is more challenging in many ways than putting together land temperature records. The difficulty with sea surface temperature is that information sources change much more than those on land.

On the land, apart from getting as many records together as possible (thank you CRU and other early collectors, and more recently ISTI), the main issues to contend with are adjusting for changes in instrument design and location. Location changes can be identified from station records or inferred from abrupt changes in the record compared with neighbouring records. Technological change hasn't happened all that often in the past 150 years or so. The main ones include the introduction of the Stevenson screen way back, and the more recent shift to automatic weather stations with resistance probes replacing mercury thermometers.

On the sea, the problems include the different sources for temperature readings: buckets of differing materials being dipped into the sea, engine room intakes, sensors on the ships hull and, more recently, drifting buoys and satellites. Within all that, scientists have to account for things like changes in the height of ship decks, interruptions to the consistency of records caused by world wars (where the data source changed from predominately merchant ships to predominately naval vessels), and more. The marvel is that researchers have worked through all these difficulties and developed records of sea surface temperature going back many decades.

Questionable peaks and troughs in the SST records - WWII and all that

One period about which most scientists who've worked on the subject have had most issue with are the years of the second world war (WWII). Some data sets show a peak in temperature that has not been easily explained by weather or climate change phenomena. In addition, previous records show a drop in the temperature around 1910 that looks a bit odd. In this paper, the authors did not find the spike that exists in ERSST v5 and to a lesser extend in HadSST3. Neither did they find the drop in temperature in the early 1900s.

In the top chart below, the hybrid record is shown in blue. The different series are a bit hard to distinguish so you might want to click on the image to enlarge it.

Figure 1 | Comparison of the coastal hybrid temperature reconstruction (using all coastal stations and fitting the global mean of the coastal temperature differences only) to co-located data from HadSST3 and ERSSTv5 for the period 1850-2016. Spatial coverage is that of HadSST3 for all of the records, with coastal cells weighted by ocean fraction.The shaded region is the 95% confidence region for the HadSST3 anomalies including combined bias adjustment and measurement and sampling errors. The lower panel shows the adjustment applied to the raw data in the HadSST3 and coastal hybrid records. A comparison with the ERSSTv4 ensemble is shown in Figure S7. Source: Cowtan 17 Figure 12.

To help see the difference, the chart below compares the Cowtan17 hybrid record with NOAA's ERSST v4 record. As discussed, the two are very similar in the most recent decades, but differ much more in the period prior to the early 1940s.

Figure 2 | Comparison of coastal hybrid temperature reconstruction to the ERSSTv4 ensemble. The dotted line is the ensemble median, while the shaded region is the 95% range of the ERSSTv4 1000 member ensemble from Huang et al (2016). DOI: 10.1175/JCLI-D-15-0430.1 . Source: Cowtan17 supporting information Figure S7

The table below highlights further that the Cowtan17 analysis is closer to the NOAA data set for the period after WWII since 1997 than it is to the Hadley record (HadSST3). The trend of HadSST3 is lower than that found in Cowtan17 and ERSST v4.

Table 1: Trend in sea surface temperature since 1997. Source: Cowtan17 Supporting Information Table S2.

The analysis supports the CMIP5 models

Another thing the analysis suggests is that there is less of a difference between observations and the blended mean from CMIP5 model runs. This is shown in the chart below, from Kevin Cowtan's briefing paper, where the green line is the CMIP5 blended mean.

Figure 3 | Comparison of global temperature records based on either the UK Met Office sea surface temperature record (HadSST3), or our coastal hybrid record. The smoothed records are compared to the average of climate model simulations from the CMIP5 project. The lower panel shows the differences between each set of observations and the models. Source: Kevin Cowtan's blog article.

Constraints and provisos

The authors of Cowtan17 show a lot of restraint and go into quite a bit of discussion of uncertainties and provisos. They present their findings not as the be all and end all of temperature reconstruction, but as a suggestion of where to investigate further. Kevin Cowtan wrote in his briefing:

However we do not necessarily trust our new record, because of the assumptions we had to make in constructing it. The most important result of our work may therefore be to identify places where extra attention should be given to addressing problems in the existing sea surface temperature records. A secondary result is that caution is required when trying to draw conclusions about any differences between the models and the observations, whether it be to identify internal cycles of the climate system or problems in the models, because the differences that we do see are mostly within the range of uncertainty of the observations.

Just the same, this paper has a lot of merit, looks at the data differently, and shows that the spurious peaks and troughs from years gone by may indeed be out of whack. It also supports the records in recent times, which seems to me to add weight to their findings.

What deniers are saying about Cowtan17

Nothing. At least nothing at WUWT or anywhere else that I've seen. Either they all missed the paper because it came out in the holidays, or they haven't figured out what to say about it.

References and further reading

Cowtan, K., Robert Rohde, and Zeke Hausfather. "Evaluating biases in Sea Surface Temperature records using coastal weather stations." Quarterly Journal of the Royal Meteorological Society (2017). DOI: 10.1002/qj.3235 (pdf here)

• Evaluating biases in Sea Surface Temperature records using coastal weather stations - overview, briefing document, links to methods and data and more from Kevin Cowtan
• Twitter thread from Zeke Hausfather

Dumb as: Anthony Watts complains Hausfather17 authors didn't use FUTURE data

Anthony Watts is complaining that scientists didn't use data that has yet to be published. What?

He did post an article about Hausfather17, which I've just written about.  Anthony's almost as nuts about this one as he was about the NOAA paper, Karl15. His headline was: Yet another study tries to erase “the pause” – but is missing a whole year of data.

The new paper uses latest available data

The new paper uses data to the end of the full year that's currently available - 2015. Since the paper would have been completed some months ago (it's just been published), not only would December 2016 data not have been available (it isn't yet), but the most recent months this year would not have been available to the authors, unless they had a Tardis.

The winner is NOAA - for global sea surface temperature

There's a new paper out that shows that, contrary to what you'll read on denier blogs, NOAA's latest version of global sea surface temperature is probably the best and most accurate around. It's the closest to observations, when you compare it to measurements from moored and floating buoys, Argo floats and radiometer-based satellite records of sea surface temperature.

Umpteen denier protests

Lamar Smith

You might remember how climate hoax conspiracy theorists, professional disinformers and other deniers protested loud and long when NOAA scientists published a paper about the revised NOAA temperature data. The US House Committee on Science, Space, and Technology, led by arch denier Lamar Smith, harassed NOAA endlessly with subpoena after subpoena. A lot of the changes to the NOAA temperature record were a result of a new version of the global sea surface temperature data set, known as Extended Reconstructed Sea Surface Temperature, or ERSST v4. The papers on that were published in February 2015 (see below). The protests only came, though, in June 2015 when there was a paper by Karl et al. That paper pushed denier buttons because it challenged the so-called "hiatus". You can read about Karl15 here, and the paper itself is here.

WUWT claims (again) that global warming is a giant conspiracy of mammoth proportions

Anthony Watts, who runs a wacky conspiracy theory blog, WUWT, has another article (archived here) claiming that global warming isn't happening and it's all a giant conspiracy. Anthony posted a "guest essay" by someone called Ralph Park, who is a conspiracy nutter.

Zeke Hausfather: Understanding adjustments to surface temperature data

This is a first. I am recommending an article that has appeared at Judith Curry's blog (archived here). It's a very good article about adjustments to surface temperature data, written by Zeke Hausfather. I couldn't see it anywhere else on the internet so Zeke may have written it for Judith and her readers. (Judith certainly needed the education. She has posted Zeke's article without comment, which is also a rare event.)

Unfortunately it means a lot of people who would benefit from reading it might miss out, because they avoid Judith's blog like the plague. On the upside, Judith panders mainly to the denialati and her readers might learn something. - Update: Note I said "might". Even at this early stage, most of Judith's readers are not interested in what Zeke actually wrote. Going by the comments they are too deep in denial and paranoid conspiracies. Updated archive is here. Sou. 12:44 am AEST Tuesday 8 July 2014

Here is an archived version of the article.

Understanding adjustments to temperature data

Zeke deals with a lot of the points raised in the recent idiocy started by "Steve Goddard" (Tony Heller) and perpetuated by Anthony Watts. He also promises two more parts, which I'll promote here when they appear, writing (my dot points):

This will be the first post in a three-part series examining adjustments in temperature data, with a specific focus on the U.S. land temperatures.

• This post will provide an overview of the adjustments done and their relative effect on temperatures. 

• The second post will examine Time of Observation adjustments in more detail, using hourly data from the pristine U.S. Climate Reference Network (USCRN) to empirically demonstrate the potential bias introduced by different observation times. 

• The final post will examine automated pairwise homogenization approaches in more detail, looking at how breakpoints are detected and how algorithms can tested to ensure that they are equally effective at removing both cooling and warming biases.

Zeke Hausfather is a researcher with the Berkeley Earth temperature analysis project.  He writes a lot for Yale Climate Connections.  If you visit some denier websites you may have seen Zeke injecting a dose of reality to contrast with the normal conspiracy theorising and other idiocy that takes place. He is known for his integrity and for being straightforward and polite with one and all. He also writes very clearly so that even people without any scientific education should be able to follow what he writes.

Understandably, Anthony Watts doesn't always get along well with Zeke. Anthony prefers FUD and denial, which Zeke doesn't do at all.

Update: Comments from Judith Curry's blog

The comments are flying thick and fast, with the emphasis on commenters being "thick", as you'd expect given the location. Here is a representative sample. Judith Curry must be very proud of herself:

David Springer is a paranoid conspiracy theorist who prefers lies to facts. I'd say he's a right wing authoritarian who distrusts any and every "official" source. He also seems to want people to believe the entire edifice of climate science rests on the weather in Washington on one day in 1988 and his lie about James Hansen. Judith does cater for weirdos, doesn't she:

 | July 7, 2014 at 10:01 am |
Good faith was undermined about the time James Hansen sabotaged the air conditioning and opened the windows to scorching outside temperatures in the congressional hearing room in 1988. Good faith collapsed completely with the Climategate emails two decades later.

Good faith my ass.

sunshinehours1 is another crank who doesn't understand Zeke's article, despite it being written so elegantly, and who doesn't know that data is available - all kinds of data including raw data as well as gridded data. Nothing is "hidden".

| July 7, 2014 at 9:55 am | 
Why do climate scientists hide the raw data? Why do they use anomalies and 5 years smoothing to hide the data?
You can’t spell anomalies with LIES.

In fact almost all of Judith's readers seem to be certifiable. Rob Bradley is no exception. From what he writes, he thinks that scientists are fudging the data. That would be a bigger hoax than could conceivably be maintained. He's an utter nutter.

| July 7, 2014 at 9:48 am |
The author states: “Their methods may not be perfect, and are certainly not immune from critical analysis, but that critical analysis should start out from a position of assuming good faith and with an understanding of what exactly has been done.”
But surely incentives matter. Peer pressure matters. Government funding matters. Beware of the ‘romantic’ view of science in a politicized area.

Scottish Sceptic is now blatantly implicitly accusing Zeke Hausfather, who is an "outsider" to climate science, of being in on the imagined "hoax". Well, we already know Scottish Sceptic is just an other utter nutter.

 | July 7, 2014 at 10:37 am | 
When an auditor checks accounts, they do not assume bad faith.
Instead they just assure the figures are right.

So, why then when skeptics try to audit climate figures do they immediately assume we are acting in bad faith?

Because academics don’t have a culture of having their work checked by outsiders

The simple fact is that academics cannot stomach having outsiders look over their figures. And this is usually a symptom of an extremely poor quality regime

claimsguy is another right wing authoritarian who distrusts scientists because they are the go-to source for science. Would he go to a barber to get an expert opinion on his medical condition?

  | July 7, 2014 at 10:47 am |
Oh geez. You’ve poisoned the well by saying Gavin liked the post.

NOAA and temperature data - it must be a conspiracy.

Update: Nick Stokes of Moyhu has written two articles that demonstrate what would happen if Anthony Watts had his way and stations with no data were ignored completely. See here and here. Anthony Watts might change his tune if he read them.

Sou 3:22 pm 1 July 2014 AEST

---

This article is about the kerfuffle that erupted between a bunch of science deniers. It all started when Steve Goddard accused NOAA and NASA of "fabricating data" (archived here).  The lie was spread all over the right wing media. Politifact and Climate Crocks among others pointed out he was wrong. Steve didn't explain how the two agencies did this. All he did was put up an animated chart that he claimed showed that the US temperature was warmer in the 1930s than at any time since. He wrote:

Prior to the year 2000, NASA showed US temperatures cooling since the 1930′s, and 1934 much warmer than 1998....Right after the year 2000, NASA and NOAA dramatically altered US climate history, making the past much colder and the present much warmer. The animation below shows how NASA cooled 1934 and warmed 1998, to make 1998 the hottest year in US history instead of 1934. This alteration turned a long term cooling trend since 1930 into a warming trend.

Steve doesn't say what data was "fabricated". Why should he? He's not a fact checker. Quite the opposite. He's in the denial business of making up stuff to stop any action to mitigate global warming.

This article is another one that's too long :( Click read more if you're on the home page.

Old and new warming in the Eurasian Arctic and denier weirdness at WUWT

Anthony Watts seems to have put his foot in it again, but has pulled it out just a little (archived here - updated here).

Today he posted an article about a new paper with some analysis of an ice core from the Eurasian Arctic, in the vicinity of the Kara and Barents Seas. Going by his note at the bottom, perhaps Anthony originally tried to use the paper to "prove" something about Cowtan and Way - maybe that it was wrong.  His note reads:

[Note: this original post was written during my workday and making a comparison to the Cowtan and Way paper, and like sometimes happens during my day, I got interrupted, and then got off on a tangent that wasn't correct. To correct my mistake, I've republished this post sans that tangent. Later I'll get back to my original idea when I have more time.  - Anthony]

My guess is that we'll be waiting for about the same length of time for him to write about his "original idea" as we'll be waiting for his promised publication about "Watts et al 2012 draft paper", which has been slipping so far down the sidebar at WUWT that it's looking as if it's about to drop right off.

Resurrecting an old favourite

In honour of this new paper, Anthony resurrected an old favourite of the denialati:

The Arctic ocean is warming up, icebergs are growing scarcer and in some places the seals are finding the water too hot, according to a report to the Commerce Department yesterday from Consul Ifft, at Bergen, Norway.

Reports from fishermen, seal hunters and explorers, he declared, all point to a radical change in climate conditions and hitherto unheard-of temperatures in the Arctic zone. Exploration expeditions report that scarcely any ice has been met with as far north as 81 degrees 29 minutes. Soundings to a depth of 3,100 meters showed the gulf stream still very warm.
Great masses of ice have been replaced by moraines of earth and stones, the report continued, while at many points well known glaciers have entirely disappeared. Very few seals and no white fish are found in the eastern Arctic, while vast shoals of herring and smelts, which have never before ventured so far north, are being encountered in the old seal fishing grounds.

The above is from a newspaper article that's been circulating among the denialati for years.  You can read the full article here.  The article describes how the west coast of Spitzbergen right up to the north was significantly warmer than normal back in the early 1920s.

It may well have been the same factors operating in both locations in the early part of last century.  The Opel paper doesn't specifically mention Spitzbergen but it does discuss Arctic-wide changes.

Here is a map of the eastern portion of the Arctic region, showing the locations of the Akademii Nauk (AN) ice core and Spitzbergen (click for larger view):

Adapted from Google Earth

AN ice core may tell 3,000 years of climate history

Back to the paper itself, which is open access.  The paper is by Thomas Opel, D. Fritzsche, and H. Meyer and published in the journal Climate of the Past.  In it, they provide more climatic information about the region as derived from an ice core.  The conclusion of the paper is that the Akademii Nauk (AN) ice core has the potential to provide a 3,000 year or so high resolution record of the climate of the western Eurasian Arctic:

The results presented in this paper highlight the potential of the AN ice core as a high-resolution climate archive for the Late Holocene, i.e. about the last three millennia. Beside a long-term decrease due to climate cooling and ice-cap growth the AN 18O record shows evidence of major temperature changes over the last millennium that are representative at least of the western Eurasian Arctic, i.e. the Barents and Kara seas region. Of particular importance are several abrupt cooling and warming events leading e.g. to the absolute SAT minimum around 1800 and the absolute SAT maximum in the early 20th century, accompanied by significant changes in sodium concentrations. The ETCW exhibits a specific double-peaked shape typical of the Barents and Kara seas region. Abrupt changes in the last centuries might be caused by internal climate dynamics related to shifts of atmospheric circulation patterns and corresponding sea-ice feedbacks.

Anthony Watts confuses local with global

I think Anthony Watts was hoping for more, maybe even proof that global warming isn't happening.   Or maybe he was hoping it showed that the Arctic summer sea ice isn't really on a death spiral.  Or maybe that "it's natural" and "it's the sun" or "climate always changes".  In his article Anthony writes (my bold italics):

Of course, just like the surface temperature record, the long term trend is up, but clearly there is also a pause since the double peak, and that’s hard to explain in the face of a linear increase of (some claim exponential) GHG emissions.

Climate shifts in the past may be "hard to explain" but not in the way Anthony suggests.  Anthony is confusing local climate with global climate.  You would think he would have learnt by now that at the regional and local level, surface temperatures don't necessarily follow global temperature trends.  But even after all his years announcing weather followed by several years blogging about it, Anthony Watts still doesn't seem to know the first thing about weather and climate.

As an aside, you'll have noticed that Anthony Watts, despite claiming to keep a climate blog, isn't even clear about the single biggest factor affecting climate today - greenhouse gas emissions.  They are indeed still rising exponentially.  It's not been a linear rise.  There are already signs that 2013 will create a new record in greenhouse gas emissions.

Climate shifts in the Arctic - a see-saw effect?

The paper provides some explanation for climate shifts in the Eurasian Arctic.  In the body of the paper the authors expand on the following relevant part of their conclusion:

Abrupt changes in the last centuries might be caused by internal climate dynamics related to shifts of atmospheric circulation patterns and corresponding sea-ice feedbacks

They discuss a possible see-saw effect operating across the Arctic at certain times, for example:

Whereas our AN 18O and the Arctic-wide SAT records (Kaufman et al., 2009; PAGES 2k Consortium, 2013) display similar patterns in the 11th and 12th centuries, they show clearly contrary trends in the 15th and 16th centuries (Fig. 6). Abrupt cooling events in the Barents and Kara seas region are accompanied by warming events on the Arctic scale and vice versa. The causes of these differences may be similar to those already discussed for the periods around 1800 and in the early 20th century. This pattern might be interpreted as a kind of SAT see-saw on a predominantly spatial scale (Eurasian vs. North American Arctic) but may contain also, to a lesser extent, seasonal effects (annual vs. summer).

The modern record at the AN ice core site

In the comments, the arguably most respected layperson who watches the Arctic, Neven, pointed out that the paper reports temperatures only up to 1998, after which temperatures are likely to have gone up even further.  NevenA says:

November 19, 2013 at 12:51 pm
That graph unfortunately ends in 1998, whereas we can safely assume that Arctic amplification and surface air temperature rate acceleration kicked in after that.

Well, Anthony didn't like that one bit.  After all, he's busy trying to prove that "all the science is wrong" by referring to the science (yeah, illogical what?).  Anthony responds in-line writing:

REPLY: simply because you say it does? Show/prove it “Gunther” – Anthony

Zeke Hausfather provided some links to temperature data for the region, at greater or lesser distances from the AN ice core.  Here is the closest record I could find at Berkeley Earth.  It is located at 79.553N 90.596E, compared to the AN core which was from 80.52 N, 94.82E.

Source: Berkeley Earth

The above station is the one referenced by Opel et al (2009), which was also the reference cited in Opel13, the paper discussed in this article.  Opel09 stated:

After a SAT maximum in the 1950s, Golomyanny data show a cooler period until 1980 and a warming trend since 1990, though without reaching the values of the 1950s.

The records for that station only go back to the 1930s, not the 1920s.  Berkeley Earth record is a bit different from Opel09, suggesting that until the last few years, the highest temperature was in the early 1940s.  I'll leave it to the experts to sort that one out.  The above record also suggests hotter than ever temperatures now, since the 2009 paper was written.

"Isolated pockets of humanity require warmth"

Anthony swings into his "UHI disease" mode and disputes temperature records he doesn't like - even when they are supported by such obvious signs of warming as the huge drop in summer sea ice in the Arctic.  I guess he still thinks that you don't need warmth to melt the ice.  Anthony makes silly comments like:
"What may be happening is that the stations that are left have a warm bias."

Zeke Hausfather points out that the recent warming in the Arctic is "not particularly controversial" and that "pretty much anywhere you look in the arctic, the land warming post-2000 is pretty remarkable".  To which Anthony sullenly and obstinately replies:

REPLY: Still, I’d like to know what individual station records are active and which ones are not – and when. One thing I’ve noted studying Arctic stations is that they all tend to be isolated pockets of humanity, which require warmth. Warmth that of course becomes local waste heat. Do you have a mechanism to show what records make up your regionalized temperature potpourri and when they were made inactive? – Anthony

Who could forget this classic case of Anthony Watts and human warmth and ice, this time in Antarctica :)

Comparing millennial records across the Arctic

In any case, the paper is more about having a high resolution millenial record of the climate for the region, not about whether the temperature this year at the site has yet reached that of the 1920s maxima - for which there is not a single unbroken source of annual or seasonal data.  (Although it does look as if it's been as hot recently if not hotter.)

Here is the chart from the paper comparing the data from the AN ice core with that of other analyses going from 1998 and back as far as 1100 years in some cases.  The AN data is in light gray for each section.  Click for larger view:

Fig. 6. AN 18O record (including linear trends for 900–1760 and 1800–1998) compared to (from top to bottom) Austfonna and Lomonosovfonna-18O (Isaksson et al., 2005), Vetreniy ice-cap 18O (Henderson, 2002; data from Kinnard et al., 2011), Arctic summer SAT anomalies (Kaufman et al., 2009), Arctic annual SAT anomalies (PAGES 2k Consortium et al., 2013), AN sodium concentrations, and Arctic sea-ice extent (Kinnard et al., 2011) records. Displayed are 5 yrm values for AN 18O (thin line), 15 yrm values for AN 18O, Austfonna and Lomonosovfonna 18O, Vetreniy ice-cap 18O, Arctic annual SAT anomalies, AN sodium concentrations and Arctic sea ice (thick lines) as well as 10 yr means for Arctic summer SAT (thick line). For easier comparison, to each graph the AN 18O 15 yrm record is added in light grey in the same scale as above and adjusted for the best fit of the 20th century maximum (except for Arctic sea ice). Abrupt warming and cooling events exceeding the dominant variability of the AN 18O record are marked by a red asterisk. Note the different scale for the Lomonosovfonna 18O record.

No medieval climate anomaly at Akademii Nauk

I expect Anthony Watts is in a bit of a bind.  He wants to use Opel13 to "prove" something about global warming.  He's not sure what he wants to prove.  He seems to have settled on the fact that there was a warm period early last century.  But then if he accepts the paper, he may be forced to gloss over the fact that there was no evidence of a medieval climate anomaly or the little ice age at that particular location.

Neither a pronounced Medieval Climate Anomaly nor a Little Ice Age are detectable in the AN 18O record. In contrast, there is evidence of several abrupt warming and cooling events, such as in the 15th and 16th centuries, partly accompanied by corresponding changes in sodium concentrations. These abrupt changes are assumed to be related to sea-ice cover variability in the Barents and Kara seas region, which might be caused by shifts in atmospheric circulation patterns. Our results indicate a significant impact of internal climate variability on Arctic climate change in the last millennium.

People who follow climate science rather than climate disinformation won't have any problem with the above.  They know that there were some regions of the world where temperatures got quite warm during medieval times (eg Greenland) and many parts of the world where it got cold in the little ice age.  They know that different parts of the world can get cold while other parts get warm and vice versa.  (Anthony Watts and his crowd find all that a bit too complicated.)

From the WUWT comments

Here are some examples of denier weirdness from the comments (archived here).

philjourdan doesn't have a clue what was reported in the paper itself but he gaily says "it's devastating":

November 19, 2013 at 12:52 pm
This paper is devastating to the whole AGW issue. Instead of seeing a rise, we now have a 60+ year pause, at least in the Arctic which is supposed to be the canary in the AGW coal mine. The pause is easily twice as long as any increase that caused the kerfuffle in the first place. In simple terms, there is no there there. We have a planet ignoring the carbon based units that inhabit it.

Espen doesn't seem to realise that Arctic warmth in the early 20th century is not news to climate scientists and says:

November 19, 2013 at 1:35 pm
Zeke Hausfather, yeah, right, so probably the current warm period in the arctic is a little warmer than the one in the early 20th century. But that pesky early 20th century Arctic warming is nevertheless a huge problem for those that desperately want the Arctic to be the canary in the AGW mine. Like, for instance, Tamino, who got so p***ed that he black listed me permanently when I used that warm period to question his toying around with Bayes theorem here.

Crispin in Waterloo but really in Ulaanbaatar makes a very odd comment about the medieval climate anomaly being a "colder deviation" and says:

November 19, 2013 at 2:25 pm
...The Medieval climate anomaly was a strongly colder deviation from the 8000 year long term cooling trend so it is probably correct to call it anomalous. We are very lucky it didn’t stay down.

Rhoda R has made up her mind about past warming, its duration and probably its location. She doesn't give tuppence for science or data and says:

November 19, 2013 at 2:40 pm
Using the term “Medieval Climate Anomaly” is an attempt by the warmist crowd to belittle the impact of sever hundred years when the climate was warmer than it is today. Using the term “anomaly” implies a brief, transient event — something not really worth mentioning.

Truthseeker ignorantly says "who cares":

November 19, 2013 at 4:24 pm
Really why do we care what the artic does? It is mostly sea ice which will have little effect on sea levels regardless of the state it is in. With less ice, navigation will become easier and less risky. It really is not important enough to waste any time or resources on.

And finally, a gem from our old mate jim Steele who says (excerpt):

November 19, 2013 at 4:58 pm Not much observational data to support warming since the 50s!

Really, Jim?

Source: Polar Science Center, University of Washington

And if you don't like "models" how about this?

---

Opel, Thomas, et al. "Eurasian Arctic climate over the past millennium as recorded in the
Akademii Nauk ice core (Severnaya Zemlya)." Clim. Past, 9, 2379–2389, 2013 doi:10.5194/cp-9-2379-2013

Opel, Thomas, et al. "115 year ice-core data from Akademii Nauk ice cap, Severnaya Zemlya: high-resolution record of Eurasian Arctic climate change." Journal of Glaciology 55.189 (2009): 21-31.