Arguments
Tree-ring proxies and the divergence problem
The skeptic argument...
Tree-rings diverge from temperature after 1960
Actual reconstructions "diverge" from the instrumental series in the last part of 20th century. For instance, in the original hockey stick (ending 1980) the last 30-40 years of data points slightly downwards. In order to smooth those time series one needs to "pad" the series beyond the end time, and no matter what method one uses, this leads to a smoothed graph pointing downwards in the end whereas the smoothed instrumental series is pointing upwards — a divergence (Climate Audit).
What the science says...
Tree growth is sensitive to temperature. Consequently, tree-ring width and tree-ring density, both indicators of tree growth, serve as useful proxies for temperature. By measuring tree growth in ancient trees, scientists can reconstruct temperature records going back over 1000 years. Comparisons with direct temperature measurements back to 1880 show a high correlation with tree growth. However, in high latitude sites, the correlation breaks down after 1960. At this point, while temperatures rise, tree-ring width shows a falling trend. This divergence between temperature and tree growth is called, imaginatively, the divergence problem.
The divergence problem has been discussed in the peer reviewed literature since the mid 1990s when it was noticed that Alaskan trees were showing a weakened temperature signal in recent decades (Jacoby 1995). This work was broadened in 1998 using a network of over 300 tree-ring records across high northern latitudes (Briffa 1998). From 1880 to 1960, there is a high correlation between the instrumental record and tree growth. Over this period, tree-rings are an accurate proxy for climate. However, the correlation drops sharply after 1960. At high latitudes, there has been a major, wide-scale change in tree-growth over the past few decades.
Figure 1: Twenty-year smoothed plots of tree-ring width (dashed line) and tree-ring density (thick solid line), averaged across a network of mid-northern latitude boreal forest sites and compared with equivalent-area averages of mean April to September temperature anomalies (thin solid line). (Briffa 1998)
Has this phenomenon happened before? In other words, can we rely on tree-ring growth as a proxy for temperature? Briffa 1998 shows that tree-ring width and density show close agreement with temperature back to 1880. To examine earlier periods, one study split a network of tree sites into northern and southern groups (Cook 2004). While the northern group showed significant divergence after the 1960s, the southern group was consistent with recent warming trends. This has been a general trend with the divergence problem - trees from high northern latitudes show divergence while low latitude trees show little to no divergence. The important result from Cook 2004 was that before the 1960s, the groups tracked each other reasonably well back to the Medieval Warm Period. Thus, the study suggests that the current divergence problem is unique over the past thousand years and is restricted to recent decades.
This suggests the decline in tree growth may have an anthropogenic cause. A thorough review of the many peer reviewed studies investigating possible contributing factors can be found in On the ’divergence problem’ in northern forests: A review of the tree-ring evidence and possible causes (D’Arrigo 2008). Some of the findings:
- Various studies have noted the drop in Alaskan tree-growth coincides with warming-induced drought. By combining temperature and rainfall records, growth declines were found to be more common in the warmer, drier locations.
- Studies in Japan and Bavaria suggest increasing sulfur dioxide emissions were responsible.
- As the divergence is widespread across high northern latitudes, Briffa 1998 suggests there may be a large scale explanation, possibly related to air pollution effects. A later study by Briffa proposed that falling stratospheric ozone concentration is a possible cause of the divergence, since this observed ozone decline has been linked to an increased incidence of ultraviolet (UV-B) radiation at the ground (Briffa 2004).
- Connected to this is global dimming (a drop in solar radiation reaching the ground). The average amount of sunlight reaching the ground has declined by around 4 to 6% from 1961 to 1990.
- One study suggests that microsite factors are an influence on whether individual trees are vulnerable to drought stress. Eg - the slope where the tree is located, the depth to permafrost and other localised factors (Wilmking 2008). This paper amusingly refers to the divergence problem as the "divergence effect" so as "to not convey any judgement by the wording" (you wouldn't want to offend those overly sensitive Alaskan trees).
There is evidence for both local and regional causes (e.g. drought stress) as well as global scale causes (e.g. global dimming). It's unlikely there's a single smoking gun to explain the divergence problem. More likely, it's a complex combination of various contributing factors, often unique to different regions and even individual trees.
One erroneous characterization is that scientists have been hiding the divergence problem. In fact, tree-ring divergence has been openly discussed in the peer-reviewed literarure since 1995. A perusal of the many peer reviewed papers (conveniently summarised in D’Arrigo 2008) reveal the following:
- The divergence problem is a physical phenomenon - tree growth has slowed or declined in the last few decades, mostly in high northern latitudes.
- The divergence problem is unprecedented, unique to the last few decades, indicating its cause may be anthropogenic.
- The cause is likely to be a combination of local and global factors such as warming-induced drought and global dimming.
- Tree-ring proxy reconstructions are reliable before 1960, tracking closely with the instrumental record and other independent proxies.
Last updated on 26 June 2010 by John Cook.
Once again you have demonstrated that you are not a publishing scientist, as anyone in the field knows how silly an accusation that is. The fame and position in science go to those who publish solid data that stands out in the field as being objectively correct. Those caught falsifying or plagiarizing data (Wegman), publishing poorly written or clearly incorrect papers (McIntyre, Spencer), or just making fantastical stuff up (Gerlich and Tscheuschner) receive no rewards in the field of science. The risk, the downside to writing bad papers or falsifying data - that's huge.
The rewards may indeed include being able to get additional grants, or rather having a slightly higher percentage of your grant applications go through - success breeds success. But please note that grants do not tend to increase the income of the scientists involved. Very few practicing scientists are in the upper 1% income levels...
On the other hand, if you wish to write advocacy papers for particular industries (Tobacco Institute, Clean Coal, Exxon, etc.), promoting a position that is not based on the science but is instead thinly disguised propaganda contrary to facts (Michals, Singer, Soon), you can get a lot of $$$ for it in "consulting fees". This is apparently driven by the billions in profits that some industries see at risk if they have to change their course of business.
This is not to say that someone writing from an "advocacy" position will always write worthless stuff - but you have to consider the motivation behind it, and judge the material accordingly.
You might note that almost all the lead AGW skeptics have think tank positions. Spencer, Michaels, Lindzen, etc.
What is the basis of your assertion that climate scientists have received billions of dollars in renumerations?
And there sure are a lot of these so-called 'think' tanks. The denial business must be berry-berry good.
For that matter, why couldn't these global conspirators get meaningful emissions cuts passed during the eight years when their alleged ringleader Al Gore was in the White House? The payoff for all the expense, lawbreaking and secret bullying it'd take to create a phony scientific consensus seems pretty paltry to me, no matter who's footing the bill.
Let's look at things realistically. You've got the oil industry, which is one of the most profitable businesses in the world, pumping huge amounts of money into government, media and pro-industry thinktanks. That's not subject to dispute. You've also got governments downplaying or ignoring scientific concerns relating to AGW. You've got hard-right politicians threatening to prosecute high-profile climate scientists like Michael Mann. And you've got large media outlets that tend to blur the distinction between, say, Lord Monckton and mainstream climate scientists.
And yet, despite all of these phenomena -- which are actually demonstrable and quantifiable -- many people still believe that someone's paying scientists all over the world "billions" to advance a theory in which the laws of physics cause the climate to behave in pretty much the way that those laws predict. For reasons no one actually knows, on the basis of evidence no one actually has. And in this narrative, amazingly, it's the climate scientists who are bullies and ideologues; the powerful interests who are casually slandering them as incompetents, frauds or worse are somehow their victims.
The theory that certain industries have spent a large amount of money to manipulate opinion for their own benefit is consistent with all of the phenomena I've brought up here. The theory that someone or other has been paying climatologists to support AGW for some nefarious reason or other is incoherent, in addition to being totally unsupported by evidence.
If you disagree, I'd love to know why.
Considering that M&M have managed to cough up a couple of papers of little interest over several years, whatever money they got, from whatever source can already be labeled as a waste anyway. McIntyre does not deserve anything remotely comparable to the attention he gets.
I'm also waiting for your comment on the computer code from M&M that sorts out upward hockey sticks on top of the pile and saves them as representative samples. How about Wegman copy and paste method? What shall we call that?
If the opposition to the theory of AGW provided an alternative theory that covers the evidence and physics even half as well as AGW, this would be an interesting conversation. There is no such alternative theory, yet some people continue to insist there must be--there must be. What do you call people who believe in a "how things work" that relies on an absent physical mechanism(s) and ignores a range of evidence?
Phillipe: Molière would salivate over the deeply hypocritical figure of Wegman and his ripe-for-satire situation.
I've seen better grant capture in many other disciplines - with nothing going into the pockets of academics.
Running a unit in a university is both extremely expensive (compared to grant levels available) and highly audited. The only way an academic can end up with some cash is through consultancy (you could easily pay 80% or 100% overheads on that also, before income tax).
No doubt he woud make a great modern Tartuffe...
Not so for "industry science". FF companies have the resources to run climate models (I work in the industry) but what would be the point? Disinformation is much cheaper. Do you think Fred Singer is going to publish data in support of AGW if that is where his "research" took him?
http://libres.uncg.edu/ir/uncg/listing.aspx?id=7935
Chris Shaker
This is clear evidence of warming. But it is not good news:
The outlook may be less favorable for the vast interior forests that ring the Arctic Circle. Satellite images have revealed swaths of brown, dying vegetation ... Evidence suggests forests elsewhere are struggling, too. In the American West, bark beetles benefitting from milder winters have devastated millions of acres of trees weakened by lack of water.
“I was expecting to see trees stressed from the warmer temperatures,” said study lead author Laia Andreu-Hayles, a tree ring scientist at Columbia University’s Lamont-Doherty Earth Observatory. “What we found was a surprise.”
http://www.ldeo.columbia.edu/news-events/trees-tundras-border-are-growing-faster-hotter-climate
Chris Shaker
Let's try less selective quote-mining and more reading for content.