Since we’re arguing over global warming this week, I thought I’d post a commentary piece that was published in the Morris newspaper this week, by my colleague Pete Wyckoff. Pete is our local tree and climate expert, who works in both the biology and environmental studies discipline, and is very well qualified to describe what was going on with some of the adjustments in the climate data that have some of the nuts screaming shrilly on Fox News.

Local Commentary: Thoughts on ‘Climate-gate’: Mitigate our impact

By Pete Wyckoff

Is the planet cooling? “I’ve just completed Mike’s Nature trick…to hide the decline,” writes climate scientist Phil Jones in a stolen 1999 e-mail which has caused a frenzy. FoxNews.com tells us that we finally have a ‘smoking gun’–proof that scientists are manufacturing a global warming crisis so that they can… they can…(I’ve never really understood the goals of the evil scientific conspirators).

The planet is warming. The data are unequivocal and based on measured temperatures (corrected for things like the “heat island” effect, so please don’t write an angry response claiming that the thermometers are wrong). What Phil Jones was referring to is something else: past temperatures estimated via tree rings. Since 1960, the rings in trees seem to have lost some of their power to record temperature.

Why should tree rings indicate temperature at all? As most of us learned in childhood, the trunks of trees at our latitude tend to put on a distinct growth ring every year. All other things being equal, when the trees are happy, they put on a large ring. When the going gets tough, the rings get thin. What makes a tree happy? Light, nutrients, lack of disease, and warmth (to a point). What do trees despise? Drought. By careful interpretation of past tree growth patterns, we can learn a lot about past climates.

Scientists have spent many years developing the techniques needed to reconstruct climate via tree rings. The problem is that in the past few decades, the tree ring-climate relationships seem to have become “decoupled” in many areas. Why? The main cause seems to be increasing atmospheric carbon dioxide. While carbon dioxide is famously a gas that heats the planet (the greenhouse effect is real and uncontroversial), carbon dioxide also directly impacts plants. Carbon dioxide fuels photosynthesis, and increased carbon dioxide in the air can both speed-up plant growth and make plants less sensitive to drought.

Decreased drought sensitivity is an expected response for plants exposed to high levels of carbon dioxide. All along the underside of a plant’s leaves are little holes called “stomata.” These holes can open and close. A tree must open its stomata to take in carbon dioxide for photosynthesis. Unfortunately, plants lose water out of their open stomata. Plants growing in air that has lots of carbon dioxide can reduce the amount of time their stomata are open, thus making them lose less water and become less susceptible to drought.

Biologists call the concept here “water-use efficiency,” and it is of crucial interest to farmers and foresters alike. Carbon dioxide causes warming that will likely make west central Minnesota a drier place in the future. At the same time, increased carbon dioxide in the air makes plants growing in our region less susceptible to drought. The balance between these two forces will be crucial.

The changing relationship between climate and tree growth is a hot topic of research at your local university. Last Friday, Dr. Chris Cole and Dr. Jon Anderson, of the University of Minnesota, Morris, published a paper in the journal “Global Change Biology” showing that aspen trees in Wisconsin are growing faster than they used to, and much of the increase is attributed to increased atmospheric carbon dioxide. Two weeks ago, a former student and I published a paper in the “Journal of Ecology” showing that oak trees in west central Minnesota became less sensitive to drought during the 20th century. If “dust bowl”-severity droughts come again soon, we project that the local oaks will suffer 50 percent less mortality than they likely did in the 1930s.

So what does this all mean? The relationship between tree rings and climate is becoming muddied by the rapid recent increase in atmospheric carbon dioxide. For most of the past 10,000 years, carbon dioxide levels in the atmosphere remained reasonably stable. Now they are skyrocketing. Modern tree rings are no longer the reliable recorders of temperature they once were. It is a good thing that we now have thermometers.

What does Phil Jones’ stolen e-mail not mean? It does not mean that global warming is a hoax. It does not mean that there are really any cracks in the scientific consensus that humans are causing dangerous alterations to the global climate.

We humans are changing the climate, largely by emitting vast quantities of carbon dioxide via the way we heat our houses, fuel our cars, and generate our electricity. This is unwise. Yes, the future climate, along with the increased carbon dioxide, may be good for some. For most people, however, the downsides of climate change are likely to far outweigh the benefits. Don’t let Fox News mislead you. As a prudent, conservative people, we should take serious steps to mitigate our impact.

Dr. Pete Wyckoff is Associate Professor of Biology at the University of Minnesota, Morris.

---

The buggy comment registration bites us again. There was an interesting discussion between a reader, Don Baccus, and Pete Wyckoff about a small misconception in his editorial. Since they couldn’t post it in a comment, I’m putting it here.

I tried to post this to PZ Myers’ blog (about tree ring proxy temp reconstructs)

But it requires registration, and when I registered, the promised confirmation e-mail never arrived (not even in my junk folder).

You’ve got the “divergence problem” backwards, I think – the problem is there’s a *decline* in the tree ring widths in recent decades, while your description of CO2 effects, if I understand correctly, would lead to an *increase*.

That’s the “hide the decline” comment, “decline” in this case refers to the “divergence problem” (divergence from the instrumental temperature record).

Several leading candidates for the cause of this problem are anthropogenic, though, primarily air pollution. And apparently none of the researchers looking into this believe that the divergence problem indicates any problem with the reconstructions deeper into the past, except possibly during periods as warm as today (but other proxies tell researchers that on a global scale, at least, there hasn’t been such a period for 1,000+ years), and where the timeframes overlap, the tree ring reconstructions map other proxy reconstructions quite nicely. The leading natural, non-anthropogenic candidate appears to be drought, i.e. at a certain temperature threshold drought dominates for those locations that show the problem (BTW not all of the tree ring reconstructions show these problems).

Here’s a recent (2007) survey paper on the divergence problem:

http://www.ldeo.columbia.edu/~liepert/pdf/DArrigo_etal.pdf

Anyway, though you might want to dig a little deeper into this …

—-
Don Baccus
http://donb.photo.net
http://birdnotes.net
http://openacs.org

This is from Pete Wyckoff:

Hey Paul (and Don),

Thanks for picking up my editorial–one of your alert readers has pointed me to an area where my thinking was perhaps muddied by my temperate forest bias. In a 2008 paper in Global and Planetary Change (vol 60, pp 289-305), D’Arrigo et al. discuss possible causes for the “divergence problem” as it applies to very high latitude tree ring records. Not only have some of those records become merely unclear (which could well be carbon dioxide-related), but the particular ring records that caused Mann et al. problems did actually show a decline in growth despite increased temperatures. (To make things even more complicated, I believe the problematic records were based on ring density, not ring width, which is the metric I use in my work). As many of your commenters have correctly pointed out, carbon dioxide fertilization and carbon dioxide-induced drought tolerance can explain the loss of a climate signal, or an artificially enhanced growth signal, but are not likely to jive with a failure to grow.

In reading D’Arrigo et al., my lay person summary for what is going on is this: the Artic is rapidly warming. The trees that we might naively expect to rejoice at this development are instead showing signs of stress. The possible reason for this (of the many presented) that I find most convincing is that the warming is changing the regional hydrology to the point where trees are drought stressed so severely that they just can’t take advantage of the warmth–despite the rise in carbon dioxide!

How did I become confused in the first place? Well, for one, I’m a scientist and I am human, and when I saw a hot topic where my own work seemed relevant (which it is), I immediately jumped to a conclusion that inflated the connection to my own work. I was also led astray by a discussion of the “hide the decline” controversy (which I found disappointingly terse) on RealClimate that linked Briffa et al’s 1998 paper “Trees tell of past climates: but are they speaking less clearly today? “

Is there a way to get this posted? I’m pretty ignorant about how the whole blog-discussion thing is supposed to work.

Back to grading. I keep resolving to give shorter finals, but I never actually follow through.

Cheers,

Pete
PS. Don Baccus seems to be both a computer guy and a excellent nature photographer. Check out his on-line galleries.

Don Baccus replies:

Thanks for the response.

The D’Arrigo 2008 Global and Planetary Change paper is probably the same paper (perhaps modified to meet reviewer critiques) that I linked to as being “in press” in 2007?

Or is it a later paper with more info? If so, I’d appreciate a URL if it’s not behind a firewall (being a humble software engineer and, as you note, photographer, I’m not plugged into the climate science/dendro/biology infrastructure and have no academic access).

It’s interesting stuff … not interesting in the way that the rabid anti-science fuckhead (pardon me!) reality-denying luddite denialsphere types are saying, though. It’s interesting in the true scientific sense … what’s going on today that causes this subset of chronologies to diverge?

Here …

” (To make things even more complicated, I believe the problematic records were based on ring density, not ring width, which is the metric I use in my work)”

Yes, “maximum latewood density” apparently jargoned into “MXD” … high altitude/high latitude trees in the right circumstances apparently (you tell me, you’re the expert!) show most growth in a few short weeks in summer, and therefore are temperature-sensitive (more weeks of sufficiently warm weather means more growth). Makes sense to me, but my professional biology experience is limited to being a field tech doing raptor migration work. All I know about plants is that sometimes they grow, sometimes they don’t, and in field camp sometimes I burn them to keep warm :) Anyway, the claim is that this is a better metric for temperature sensitivity than simple tree ring width, and I believe it, from what I’ve read. In the sense that I trust experts, just as I’d hope you’d give me similar respect if you asked me about a computer science question.

“The possible reason for this (of the many presented) that I find most convincing is that the warming is changing the regional hydrology to the point where trees are drought stressed so severely that they just can’t take advantage of the warmth–despite the rise in carbon dioxide!”

This is the leading non-anthropogenic candidate …

I think the major problem researchers are having with this, though, is that the divergence problem is sort of randomly distributed with no immediately obvious correlation with available precip info. Then again, by definition, “high latitude” means “remote” and “no nearby (usually) met stations” so microclimate etc problems are well, problems. But I do think this is a very strong candidate (and if D`Arrigo 2008 states this more strongly, beyond her 2007 draft, perhaps even stronger, I’d like to read the latest paper rather than just the 2007 draft).

But all that holds true for possible anthropogenic causes. There’s a lack of localized data, I think that’s a big problem here in terms of pinning down the cause of the divergence problem.

But none of this seriously calls into question reconstructions that match available proxy and instrument data for like 90% or so of the period in which the data overlaps. Even the recent divergence problem in areas that have long term data available overlaps with thermometers for about 2/3 of the historical record (one reason why they think that some anthropogenic cause might be there, or a temperature threshold causing drought cause (which would make the denialist claims of a “warm as today” MWP even weaker than they are now, because you don’t see divergence back then)).

And of course, there are chronologies that don’t show the divergence problem at all, something the denialists are strangely quiet about …

Anyway the rational response to the divergence problem is to research it. Not to use it as a basis for claiming that all of science that might bear on climatology is a fraud :) I know I’ll be interested in what researchers find out about this over the next five to ten years …

Thank you very much for your response, and for taking the time to do some reading based on my e-mail, and for taking the time to respond.

And, PZ, thank you for being such a bulldog for what’s right and against what’s wrong.

PS. Don Baccus seems to be both a computer guy and a excellent nature photographer. Check out his on-line galleries.

And thanks for that, too :)

—-
Don Baccus
http://donb.photo.net
http://birdnotes.net
http://openacs.org

And one more from Baccus:

On Dec 17, 2009, at 8:31 PM, Peter Wyckoff wrote:

How did I become confused in the first place? Well, for one, I’m a scientist and I am human, and when I saw a hot topic where my own work seemed relevant (which it is), I immediately jumped to a conclusion that inflated the connection to my own work. I was also led astray by a discussion of the “hide the decline” controversy (which I found disappointingly terse) on RealClimate that linked Briffa et al’s 1998 paper “Trees tell of past climates: but are they speaking less clearly today? “

Regarding the Real Climate stuff … the terseness comes, partly, I believe, from the fact that climate science is so under the microscope that the anti-science/pseudoscience and the rational people share vocabulary and background to such an extent that such terseness is perfectly clear to those of us who are fixated on it.

Not much different than the biology vs. genesis (in all its permutations) debate. We all can talk in code, now, and if you don’t know it, it can seem terse.

Oh, and I missed that Real Climate link to the 2008 paper, I’d found the D’Arrigo 2007 in press work via google …

BTW I hope you don’t think that I don’t think you or any working scientist isn’t human, and are incapable of making mistakes, or having human feelings, and all that :) Or that your response in any way reflects on your expertise in the stuff you work on.

Is there a way to get this posted? I’m pretty ignorant about how the whole blog-discussion thing is supposed to work.

The way it’s supposed to work is that working scientists are supposed to be shouted down and humiliated by torch-burning, castle-storming Rush Limbaugh-worshipping “true Americans”. Filmed in black-and-white like the original Frankenstein movie, appropriate for the anti-progress mindset of these people.

And if scientists don’t crawl away and hide their research … death threats, attempts to get them fired, censured, etc.

(I’m not kidding, one climate scientist in Texas was given a police bodyguard before giving a talk in the last couple of months because of death threats, and scientists at CRU and Ben Santer at LLNL have gotten death threats, Ben Santer as far back as 1996, and they’re not the only ones). At this week’s AGU, a scientist at Penn State said an alumni tried to get him fired for saying “there’s no peer reviewed papers that overturn mainstream climate science” (paraphrase). James Hansen reports he and his co-workers are now spending much of their time working on FOIA requests that ask for all their correspondence to be released into the public domain.

Fear for science, dudes. The far right, especially here in the US, wants to bury science in the name of both extreme biblical literalism and libertarianism.

Anyway, thanks again, Peter, for your response.

—-
Don Baccus
http://donb.photo.net
http://birdnotes.net
http://openacs.org