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The CRU hack

Filed under: — group @ 20 November 2009

As many of you will be aware, a large number of emails from the Climatic Research Unit (CRU) at the University of East Anglia webmail server were hacked recently (Despite some confusion generated by Anthony Watts, this has absolutely nothing to do with the Hadley Centre which is a completely separate institution). As people are also no doubt aware the breaking into of computers and releasing private information is illegal, and regardless of how they were obtained, posting private correspondence without permission is unethical. We therefore aren’t going to post any of the emails here. We were made aware of the existence of this archive last Tuesday morning when the hackers attempted to upload it to RealClimate, and we notified CRU of their possible security breach later that day.

Nonetheless, these emails (a presumably careful selection of (possibly edited?) correspondence dating back to 1996 and as recently as Nov 12) are being widely circulated, and therefore require some comment. Some of them involve people here (and the archive includes the first RealClimate email we ever sent out to colleagues) and include discussions we’ve had with the CRU folk on topics related to the surface temperature record and some paleo-related issues, mainly to ensure that posting were accurate.
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A problem of multiplicity

Filed under: — rasmus @ 20 November 2009

One thing a scientist doesn’t want to mess up is the problem of multiplicity (also known as ‘field significance‘). It’s just like rolling a die 600 times, and then getting excited about getting roughly 100 sixes. However, sometimes it’s much more subtle than just rolling dice.

This problem seems to be an issue in a recent by paper with the title ‘Evidence for solar forcing in variability of temperatures and pressures in Europe‘ by Le Mouel et al. (2009) in the Journal of Atmospheric and Solar-Terrestrial Physics.

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A Treeline Story

Filed under: — Ray Bradley @ 17 November 2009

Some of the highest growing trees in the world are also the oldest—bristlecone pines (Pinus longaeva) from the Great Basin in the western United States (eastern California, Nevada and Utah). The oldest example is more than 4800 years old. Because of their longevity and growth at high elevations (where the growth of trees is generally known to be limited by temperature) bristlecone pines have been of particular interest to dendroclimatologists (paleoclimatologists who study tree rings to reconstruct past climate). Numerous ecological studies carried out at treeline sites all over the world show that temperature imposes a critical limitation on the ability of trees to produce new tissue; mean daily temperatures of 8-9°C are required, so recent warming will have particular benefits for those trees that have managed to eke out an existence for so long, living “on the edge”.

An interesting characteristic of the western bristlecone pines is that their recent growth has markedly increased—ring widths have been higher than in previous decades. Previous studies have debated to what extent this “fact” is real, or just an artifact of the way tree-ring data are analyzed. Because the growth of trees is radial, as trees get older and the diameter of a tree increases, annual ring widths decline in thickness. This is the normal “growth function” that is commonly removed from measurements before further analysis is carried out. The trick is to do this carefully so that as much climate information is retained while the growth function is discarded, and dendroclimatologists know how to do this quite well. However, sometimes the “standardization” procedure can introduce spurious results. This led some to regard the apparent growth increase in bristlecone pines to be a meaningless result of the data processing. In a new article in the Proceedings of the U.S. National Academy of Sciences (PNAS) Matthew Salzer (Laboratory of Tree Ring Research, University of Arizona) and colleagues examine this issue head on. They studied hundreds of trees from treeline sites in the Great Basin, aligned all the samples according to date, and simply averaged the results (Figure 1). Given that these trees are all long-lived, the complicating factor of growth function (which is strongest for the early growth of a tree) was not significant for assessing the most recent growth. Their results show that mean ring width in the last 50 years has been greater than in any previous 50 year period over the last 3700 years. You have to go all the way back to ~1900-1300 B.C. to find mean ring widths approaching recent values. Furthermore, the recent increase in ring widths is seen in trees at the upper forest border at sites hundreds of km away (even when the treelines there were at lower elevations)—but not in trees below the upper forest border. Below the zone closest to treeline, wide rings are formed in cool, wet years, and narrow rings in warm, dry years, and trees from this lower zone do not show the 20th century growth surge.

It is thus clear that the bristlecone pines from the highest regions, close to their growth limit, are showing a very strong response to recent warming, and indicating just how unusual it has been in the context of the last few millennia. Previous explanations have focused on possible CO2 fertilization effects (increasing water use efficiency) but there is no obvious reason why such factors would have affected only trees within approximately 150m of local treeline in different locations. Rather, the high elevation trees, close to the limit of growth, have responded positively to the recent increase in temperature just as ecological studies would have predicted.

One final note: bristlecone pines often have an unusual growth form known as “strip bark morphology” in which annual growth layers are restricted to only parts of a tree’s circumference. Some studies have suggested that such trees be avoided for paleoclimatic purposes, a point repeated in a recent National Academy of Sciences report (Surface temperature reconstructions for the last 2,000 years. NRC, 2006). However Salzer et al’s study shows that there is no significant difference in their results when the data are divided into two classes—strip bark and non-strip-bark cases –when the raw unstandardized data are compared. So that particular issue has apparently had people barking up the wrong tree…

Figure 1: Median ring-widths (non-overlapping 50-year means) of upper forest border Pinus longaeva from 3 sites in western North America, plotted on first year of interval (from Salzer et al, PNAS, 2009)

It’s all about me (thane)!

Filed under: — gavin @ 12 November 2009

Well, it’s not really all about me. But methane has figured strongly in a couple of stories recently and gets an apparently-larger-than-before shout-out in Al Gore’s new book as well. Since a part of the recent discussion is based on a paper I co-authored in Science, it is probably incumbent on me to provide a little context.

First off, these latest results are being strongly misrepresented in certain quarters. It should be obvious, but still bears emphasizing, that redistributing the historic forcings between various short-lived species and CH4 is mainly an accounting exercise and doesn’t impact the absolute effect attributed to CO2 (except for a tiny impact of fossil-derived CH4 on the fossil-derived CO2). The headlines that stated that our work shows a bigger role for CH4 should have made it clear that this is at the expense of other short-lived species, not CO2. Indeed, the attribution of historical forcings to CO2 that we made back in 2006 is basically the same as it is now.
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Muddying the peer-reviewed literature

Filed under: — gavin @ 11 November 2009

We’ve often discussed the how’s and why’s of correcting incorrect information that is occasionally found in the peer-reviewed literature. There are multiple recent instances of heavily-promoted papers that contained fundamental flaws that were addressed both on blogs and in submitted comments or follow-up papers (e.g. McLean et al, Douglass et al., Schwartz). Each of those wasted a huge amount of everyone’s time, though there is usually some (small) payoff in terms of a clearer statement of the problems and lessons for subsequent work. However, in each of those cases, the papers were already “in press” by the time other people were aware of the problems.

What is the situation though when problems (of whatever seriousness) are pointed out at an earlier stage? For instance, when a paper has been accepted in principle but a final version has not been sent in and well before the proofs have been sent out? At that point it would seem to be incumbent on the authors to ensure that any errors are fixed before they have a chance to confuse or mislead a wider readership. Often in earlier times corrections and adjustments would have been made using the ‘Note added in proof’, but this is less used these days since it is so easy to fix electronic versions.
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