Divergence problem solved (allegedly)

An article in Newsweek is claiming that the divergence problem has been solved:

[The] solution is simple, elegant, and intuitive: global dimming. Since the 1960s—exactly when tree-ring data started to go awry—“there’s been large scale decreases in the amount of light that’s reaching the earth,” says Stine. It’s fairly easy to see why, too. In rapidly industrializing parts of the world with fewer emissions laws—like Southeast Asia—the light decline is particularly steep, and continues into the 21st century. On the other hand, in areas like the U.S. and Europe, you see a rapid decline in the middle of the 20th century, but then light levels steady themselves later on—right around the time most air pollution laws were put into place.

The article is largely the normal news magazine misrepresentation of Climategate and the scientific issues around temperature reconstructions and is not really worth the time of anyone other than the global warming faithful. However, the source of the alleged breakthrough is a paper by AR Stine and Peter Huybers, published in Nature Communications.

Annual growth ring variations in Arctic trees are often used to reconstruct surface temperature. In general, however, the growth of Arctic vegetation is limited both by temperature and light availability, suggesting that variations in atmospheric transmissivity may also influence tree-ring characteristics. Here we show that Arctic tree-ring density is sensitive to changes in light availability across two distinct phenomena: explosive volcanic eruptions (P<0.01) and the recent epoch of global dimming (P<0.01). In each case, the greatest response is found in the most light-limited regions of the Arctic. Essentially no late 20th century decline in tree-ring density relative to temperature is seen in the least light-limited regions of the Arctic. Consistent results follow from analysis of tree-ring width and from individually analysing each of seven tree species. Light availability thus appears an important control, opening the possibility for using tree rings to reconstruct historical changes in surface light intensity.

It seems that trees whose growth was said to be limited by temperature are actually sometimes limited by something else altogether.

This is one for Mr McIntyre, I fancy.

Ye olde techniques - Josh 273

 

I thought the National Review article, posted here of course, was worth a cartoon. H/t Rick Cina in the comments for the peer-reviewed critiques of Mann's hockey sticks.

Cartoons by Josh

More Briffa vs Ridley

There has been another exchange between Keith Briffa and Matt Ridley in the pages of the Times. Briffa's new letter was as follows:

Sir, Matt Ridley’s response (Jan 17) to my letter further confuses and misrepresents the issues.

He says that I said I reprocessed a tree-ring data set “rather than ignoring it because it gave less of an uptick in temperatures in later decades than the small sample of Siberian larch trees” that I published.

What I in fact said was that I reprocessed the same data set used by different researchers in their version of this chronology. This was in order to improve the representation of long-timescale information in these data. Ridley persists in the repeated claim that a “larger tree-ring chronology from the same region did not have a hockey stick shape”, implying that a chronology based on more tree-ring data would invalidate our conclusions and insinuating that just such an “adverse” chronology had been concealed by us and would not have come to light without a Freedom of Information (FOI) request. He is wrong on both counts. An FOI request was made to the University of East Anglia for a chronology whose existence was revealed as a result of the theft of emails from the Climatic Research Unit. The Information Commissioner’s Office and the Information Tribunal rejected this request, accepting our explanation that the chronology in question was produced as part of ongoing research intended for publication. This chronology was subsequently published, but as a demonstration of how a failure to recognise and account for inhomogeneities in the underlying measurement sets can produce an unreliable indication of tree growth and inferred summer temperature changes.

Ridley quotes me as saying my “research was validated by the inquiry chaired by Sir Muir Russell.” I said no such thing. The Independent Climate Change Email Review had no remit to “validate” any research. What I actually said was that I had not “cherry-picked” my data to produce a desired result, which was the specific accusation levelled at me in Ridley’s piece (Opinion, Jan 6). Sir Muir Russell’s team examined this specific accusation and found that I had not.

Professor Keith R. Briffa

Matt has sent  me a copy of his response which is as follows:

Click to read more ...

Solid rock

Yesterday Michael Shermer, the founder of the Skeptics Society, issued one of those mildly irritating calls for global warming sceptics to run up the white flag:

Libertarians, tea partyers, & free market advocates: you're on the wrong side of the climate issue. The science is rock solid. Follow data.

Being a global warming sceptic who falls into more than one of the categories mentioned, I asked Shermer whether he wanted to discuss the issue or whether he was in broadcast mode. As he didn't reply I proceeded to press him to explain exactly what was the science was that he felt was "rock solid" - was it cloud feedbacks, uniform priors in ECS, deep ocean heat transport, climate models? Libertarian sceptics wanted to know.

Click to read more ...

Geological Society does woo!

From time to time I have noted the pronouncements issued by the Royal Society, and observed that those at the helm have used and abused the society's good name in order to advance their own political agendas: the fellows are rarely if ever consulted about the policy positions that are taken in their name.

Today the Geological Society has issued an addendum to its position paper on climate science, which appears to have been put together in exactly the same way.

Click to read more ...

Wilson on millennial temperature reconstructions

Last week I attended a lecture given by Rob Wilson at the University of St Andrews. This was a two-hour marathon, a format that is excellent if your lecturer is good enough to carry an audience, as it enables issues to be addressed in much more depth than is the norm. In the event, the time shot by, and if you read on you will see why.

Rob was doing a review of the millennial temperature reconstructions, following the story from the First Assessment Report through to AR5. As readers here know, Rob is no kind of a sceptic (a point he repeated over lunch), but on the northern hemisphere paleo studies his position is not a million miles away from mine. In places our positions are identical, as you will see.

Click to read more ...

The ancient history of the Hockey Stick

Bernie Lewin is in the blogging saddle again and has written a fascinating account of the early history of the millennial temperature reconstructions.

There is one temperature reconstruction of the last millennium that skeptics love to hate. And there is another that skeptics idolize in its place. The one is the ‘Hockey Stick’ northern hemisphere reconstruction, while the other appears as a schematic global trend line in the First Assessment Report of the IPCC. But neither graph is any good. They both obscure and distort the underlying science. Moreover, the skeptic’s idol itself usurped yet another dubious graph that reigned through the late 1970s and early 1980s. Thus, since global climate change anxiety emerged in the 1970s, we find a succession of three iconic millennium temperature graphs, each as different from the other as they are obscure in their scientific grounding. What is strange is that such plastic transformations are not found with the conventional reconstructions at smaller and larger timescales. The trend on the geological scale was only being refined over the same period. The large scale 100-year trend line has been more controversial. But both have maintained their general characteristics throughout the cooling and then warming alarm. So, what is it about the 1000-year timeframe? In the next couple of posts we uncover the origins of the two predecessors to the Hockey Stick. While the earliest version is as obscure in its origins as it is forgotten today (Part II not yet posted), the other remains the idol of the skeptic (Part I). And so smash it we do!

I'm not sure that the Lamb hockey stick is idolised as such, but this probing into the early history of the paleoclimate scene looks as though it will be pretty interesting. Read the whole thing.

Von Storch on the models again

In a post at Klimazwiebel, Von Storch and Zorita have expanded onf the views they put forward in the discusion paper I mentioned the other day.

We want here to set straight some misinterpretations that may have arisen in the blogosphere, e.g. Bishophill, and may also have been present in the review processes by Nature as well.

The main result is that climate models run under realistic scenarios (for the recent past) have some difficulty in simulating the observed trends of the last 15 years, and that are not able to simulate a continuing trend of the observed magnitude for a total of 20 years or more. This main result does not imply that the anthropogenic greenhouse gases have not been the most important cause for the warming observed during the second half of the 20th century. That greenhouse gases have been responsible for, at least, part or even most of the observed warming, is not only based on the results of climate simulations, but can be derived from basic physical principles, and thus it is not really debated. It is important to stress that there is to date no realistic alternative explanation for the warming observed in the last 50 years. The effect of greenhouse gases is not only in the trend in global mean near-surface temperature, but has been also identified in the spatial pattern of the observed warming and in other variables, such as stratospheric temperature, sea-level pressure and others.

Although von Storch and Zorita talk of misinterpretations, I'm not sure there is any great difference between what they say here and what I concluded last week. At the time I said that the models are falsified - they run too hot. A model that had a slower rate of warming would not be. So a claim that part of the observed warming is anthropogenic is still scientifically tenable. How big a part is manmade is, given the failure of the models, anyone's guess.

I'm not, however, convinced that the only plausible explanation for the warming of the last 50 years is greenhouse gases. As I mentioned the other day, the IPCC looks set to conclude that there was a Medieval Warm Period. Last time I heard Rob Wilson discuss the matter, he said that the climate models couldn't even get the MWP in the right historical position, let alone explain its apparently large magnitude.

So once again I find myself returning to the point I make so often. The unknown unknowns are a big problem. Scientists would do themselves a favour if they recognised it.

[Comments will be tightly edited for relevance and tone]

IPCC to admit MWP warmer?

The Washington Post has further leaks from the IPCC's Fifth Assessment Report. They can be seen here.

The conclusions about the millennial temperature reconstructions...

The 30 years from 1983-2012 was very likely the warmest 30-year period of the last 800 years.

are interesting when compared to what was said last time round:

Average Northern Hemisphere temperatures during the second half of the 20th century were very likely higher than during any other 50-year period in the last 500 years and likely the highest in at least the past 1,300 years.

The shift from 50-year periods to 30 years periods makes direct comparison difficult, but this does seem to suggest something of a reining back. The Medieval Warm Period, located by AR4 in the centuries spanning the end of the first millennium, is now apparently accepted as probably being warmer than the current warming, at least if the Washington Post is to be believed.

Gore drops Mann

Anthony has a really interesting post from a spy inside one of Al Gore's Climate Leader training programs. Read the whole thing, but I thought this was particularly interesting.

Al Gore himself went through the entire slide show that we are supposed to use as his “Climate Leaders.”  Quite honestly, there is nothing new here, EXCEPT that there is no trace of the “hockey stick” graph that was so central to “An Inconvenient Truth”!! Amazing, considering how central that was to their arguments!

Improving peer review

Discover Magazine considers a new proposal for eliminating some of the bias from the peer review process.

...scientific manuscripts should be submitted for peer review with the results and discussion omitted. The reviewers would judge the submission on the strength of the methods and the introduction alone. If they recommended publication, the authors would then send them the full paper.

The reviewers would then have a chance to change their mind and reject it, or ask for further experiments to be carried out, but the ‘bar’ for this to happen would be high.

This is quite a neat idea, potentially removing much of the bias in the peer review process. Other problems would, however, remain. For example, You can imagine a paper that began "we updated all the major tree ring temperature proxies in North America and northern Europe" being rejected out of hand - there are some questions that people just don't want answered.

Yamal no more

Steve McIntyre has released a sudden flurry of blog posts on the subject of the Briffa et al 2013 paper. Today's offering contains the eye-opening news that CRU have finally backtracked from the Yamal hockey stick of "most important tree in the world" fame. The new version of the series is no longer hockey stick shaped and the modern portions resemble closely the versions of Yamal posted at Climate Audit as long ago as 2009, for which McIntyre was resoundingly condemned by mainstream climatologists.

Update on Jun 30, 2013 by Bishop Hill

Rob Wilson sends this sensitivity analysis for the D'Arrigo et al 2006 paper, so that people can see the effect of excluding Yamal. Rob writes:

Below compared are mean NH composites (z=scores w.r.t. 1750-1950). Show[n] for period with at least 2 chronologies per continent (American and Eurasia).

Red line is DWJ06 without Wrangells or Yamal - little change.

Green line is an extended version of the Wilson et al. 07 study. Completely independent data-set to DWJ06

D'Arrigo et al was discussed in the Hockey Stick Illusion, where I noted that it includes some other dubious series, including Tornetrask. So while a lack of sensitivity to Yamal is interesting, I'm not sure I'm convinced yet. It would be interesting to know which series are driving the hockey stick shape, or whether it's a function of the methodology or something.

Radial pulses

Good to Steve M back in the saddle at CA, where he notes some comments of Keith Briffa's that would seem to condemn much of the IPCC's millennial temp reconstruction corpus to oblivion:

I very much welcome the strong position taken by Briffa and coauthors against the use of radially deformed tree ring data. I look forward to the prompt application of these standards by Mann and others to strip bark chronologies. Given realclimate’s endorsement of [Briffa 2013], I presume that realclimate will urge that all reconstructions relying on bristlecones be recalled pending assessment of radial deformation and inhomogeneity according to [Briffa 2013] standards.

Met Office withdraws article about Marcott's hockey stick

The Met Office's My Climate and Me website has removed a blog post about the Marcott Hockey Stick:

We previously posted an article entitled “New analysis suggests the Earth is warming at a rate unprecedented for 11,300 years” covering the paper by Marcott et al in Nature. The title of our article drew on the original press release for the paper.  However, we note that authors of the paper have since issued an extensive response to media coverage [http://www.realclimate.org/index.php/archives/2013/03/response-by-marcott-et-al/] which includes the following statement:

Click to read more ...

Tamsin's SciFoo talk

Tamsin Edwards points us to the talk she wants to give at Google's prestigious SciFoo conference. It's called "Tea with the Enemy".

Some science has a bad relationship with the public: in particular, climate science and many life sciences. Whether due to misinformation or misunderstanding, controversy or contested results, politicisation or fear - or all of these - such scientific "hot potatoes" are dangerous because non-experts must engage with, trust, and understand scientific results to make well-informed decisions about themselves and society. They can also damage the reputation of science in terms of its impartiality or aim to improve human understanding and quality of life.

Click to read more ...