Oxygen Isotopes in Tree Rings a Poor Yardstick of Climate Change
For many years certain paleobotanists have claimed that the oxygen isotope ratios in tree rings are indicators of the temperature during the growing season that the ring developed. They have used the O isotope ratio to “reconstruct” past climates as evidence of climate change.
Now it turns out that theory is highly questionable. New findings, to be published in an upcoming issue of Nature, indicate that tree leaves photosynthesize at a constant temperature. From ScienceNews [here]:
Goldilocks tree leaves
By Susan Milius, ScienceNews, June 11th, 2008
Sweating in the heat or huddling in the cold keeps temperatures favorable
Tree leaves do a pretty good job of achieving temperatures that are just right for photosynthesis, even if it’s too hot or too cold where they live, a new study shows.
From roughly the top to the bottom of North America, across some 50 degrees of latitude, trees all do their photosynthesizing at leaf temperatures around 21.4° Celsius plus or minus 2.2 degrees, says physiological ecologist Brent Helliker of the University of Pennsylvania in Philadelphia. That conclusion was based on a broad survey of the ratios of two forms of oxygen that vary depending on the temperature and humidity of leaves. Those properties control evaporation and make a signature in the cellulose of the tree rings, Helliker and colleague Suzanna Richter report in an upcoming Nature.
Such temperature control undermines the assumption that the insides of leaves have the same temperature as the air, Helliker says. That’s an assumption underlying studies that check oxygen ratios in old tree tissue to reconstruct past climates, he says.
The tree-ring community is just starting to sort out what the finding means. “I, and I am sure my colleagues in isotope dendroclimatology, will welcome this paper because it improves our understanding of the complex relationship between climate and the stable isotope ratios in wood,” says Danny McCarroll of the University of Wales Swansea. However, he objects to Helliker’s claim that paleoclimatologists’ approaches have relied so heavily on whether leaf temperatures match those of the surrounding air.
McCarroll attempts to defend climate studies that use O isotopes as temperature proxies by saying that such studies don’t exist, that nobody “relied so heavily” on the O isotope proxies. However, numerous such studies do exist, and the authors of those indeed relied very heavily on the supposed correlation (which Helliker and Richter have shown to be spurious). A few examples of climate change studies that depend on O isotope ratio as a proxy for temperature are here, here, here, here, here, here, here, and here.
Far from being a rare thing, the O isotope-tree-ring-climate-change alleged correlations are quite popular in some scientific circles. But now the findings of scientists who followed that fad must be seriously doubted. Shock and awe has set in at the tree ring labs. More from the ScienceNews article:
Those paleoclimatology methods for using isotopes in tree rings to reconstruct climate have been validated by observations, says Jan Esper of the Swiss Federal Research Institute in Birmensdorf. “From this perspective, the findings by Helliker and Richter are indeed surprising, as I would have expected a closer association between leaf and surrounding air temperature,” he says.
That was the old theory, but now it must be discarded. The alleged “validation by observation” was faulty, if in fact it ever occurred at all. Evidently, the observers were fooling themselves. Brent Helliker and Suzanna Richter just monkey-wrenched all that nonsense:
Helliker says he has been bugged for years by the assumption that a tree leaf photosynthesized at whatever the local air temperature might be. Trees release water, and during hot times, that botanical sweat cools them down. And trees that grow in cold places tend to cluster their leaves. These tight formations can affect the rate at which leaves lose heat on cold days, just as fingers pressed together in mittens stay warmer than fingers separated by space in gloves.
Physiologists, of course, could measure the temperature on individual leaves, but measuring enough leaves to give a picture of the canopy has been difficult. Helliker estimates that scientists would need at least 140 leaves to get a valid reading for the temperature of photosynthesis of a single tree.
His colleague Richter, however, had collected tree ring data for another project, and Helliker realized it would be perfect to test his idea. Richter had not only recorded oxygen ratios in the tree rings, but had also collected data from nearby weather stations on relative humidity. Since she knew the humidity, the researchers could calculate what the leaf temperature must have been to produce particular ratios of oxygen isotopes.
When the leaf is photosynthesizing, the sugars it produces include oxygen in the temperature-sensitive ratio. The cellulose in tree rings made from these sugars thus indicates the leaf temperature during photosynthesis.
What Helliker and Richter found was a constant temperature of photosynthesis, not a variable one. That is a very significant new finding, one that challenges an old paradigm.
“What I like about this paper is the fact that it highlights the need to account for actual life conditions,” says Christian Körner of the University of Basel in Switzerland.
Empirical evidence, actual life conditions, trump the theoretical climate change models. Those models were based on a flawed theoretical premise. Now we know that the O isotope ratio in tree rings does not reflect or record the ambient air temperature of the growing season.
Empirical evidence is the smoking gun that throws the pretty theories out the window. In this case, the theories discarded are climate change models.
And logically, we must also throw out the dire predictions of those climate modelers regarding the alleged effects of alleged climate change on tree growth. It turns out trees are quite adaptive and grow about the same regardless of ambient air temperature.
When climate alarmists claim (as they are wont to do) that a one or two degree change in global temperature will devastate forests, they are engaging in non-scientific hysteria. Our forests have been growing where they have grown during the entire Holocene, despite 5-degree C swings in global temperature during our interglacial era.
When Tom Swetnam declared on 60 Minutes last August that half our forests will die off during the global warming he and Al Gore predict will occur this century, he was blowing non-scientific smoke. He was wrong-ola, which is very wrong. But you already knew that, right?
by cmb
The new findings are these: global warming is a hoax, and forest die-offs due to non-existent global warming are bogus predictions.
The old findings are that our current forest species occupied the land shortly after the retreat of the ice caps about 12,500 years ago. With few exceptions, the current forest species have survived through all the climate variation that has occurred in the Holocene, including the Climatic Optimums of 9,000 and 6,000 years ago when it was much warmer than today.
To review: (1) our forest species can survive in much warmer climates; (2) it’s not getting warmer anyhow, so it’s a moot point.
The only forest dieoffs we are experiencing are due to human-induced holocaust forest fires that have resulted from abandonment and unmanagement. It’s the lack of stewardship, not AGW, that’s killing our forests.
by cmb
The thing to remember here is that anyone telling anyone else that GW is a hoax is pulling their leg. It is now accepted as fact by every reputable scientific organization and national government planetwide.
And, of course, any claim that it’s not getting warmer goes against every verified scientific finding on that subject, from proxies to direct satellite measurements.
There’s certainly no need to take my word for any of the above, and it’s disappointing to see this sort of dishonest article on something calling itself an institute.
I’ll repeat my call for the gap between the research findings and the overblown posturings in the article to be fixed. Until they are, it is simply an example of willfully ignorant propaganda.
No, cmb, global warming is a hoax and every reputable scientific organization is today calling it so. Even the IPCC has backed off, claiming now that GW is, in fact, not happening, and will not happen for at least one more solar cycle (12 years), if ever.
The GW hoax is widely discussed on the Internet. I recommend ICECAP [here], Watt’s Up With That [here], Global Warming Hoax [here], Climate Skeptic [here], Climate Audit [here], and Global Warming Skeptics [here], just to name a few.
The consensus today is that solar cycles and solar irradiance drive global temperatures, not greenhouse gases, of which CO2 is a very minor component anyway. The direct satellite measurements are all in accord that there has not been any global warming since 1998, despite marginally rising CO2 concentrations (~10 parts per million). Indeed, 2008 has been the coldest year since the 1970’s, and every indication is that global temperatures will continue to fall due to the delayed Solar Cycle 24 and the decline in solar storms.
The propaganda, as you call it, emanates from political organizations, not scientific ones. That propaganda has many facets, but one which troubles me the most is that the GW hoax is being used as an excuse to murder forests. Our crisis of catastrophic forest fires has nothing to do with global temperatures and everything to do with deliberate destruction by federal land management agencies.
Instead of blaming a non-existent factor, we should be zeroing in on the real causes of forest destruction: an unwillingness to protect, maintain, and perpetuate America’s priceless heritage forests. Abandonment is not stewardship. That is the crux of the problem, and at W.I.S.E. we strive every day to eliminate the ignorance that underlies it.
Our Library is growing. In it we are posting the most advanced, cutting-edge, scientific research, papers, and books that represent the new paradigm in forestry and environmental science. They all acknowledge anthropogenic influences, not over climate but upon our landscapes by human residency and stewardship for the last few thousand years. That is the information you seek, and we are providing it free of charge to you. Please peruse the W.I.S.E. Library and our Colloquia to gain a better understanding of environmental science today.
by Joe B.
Anyone telling anyone that we are causing or can reverse global warming by exchanging our SUVs for a damn electric golf cart is doing more than pulling our leg, they are helping Marxists destroy freedom.
Look, I know MSNBC hasn’t caught on yet, so you and your information are behind the times, but Global Warming is a hoax. They created Climate Change terminology just in time to try to save the fact that every reputable scientist was coming to the conclusion that it is far left lunacy to put the entire onerous of the destruction of the earth on engines that run on fossil fuels.
cmb, I want you to use common sense and tell me what is a more likely factor as to the temperature on this planet. Is it more likely this planet’s temperature is controlled by a nearby star, a favorable atmosphere and the geothermal events that occur as this planet tries to realign the pieces of the puzzle that are the plates?
Or is it more likely that the popularization of sport utility vehicles has been driving up the planet’s temperature? Also, if this is so, please explain the lack of a temperature increase for the last decade? Also, please explain to me (without a Flintstone’s reference) just how in the hell this planet warmed up enough to melt the last glaciers of the last ice age; you may know of that time period as the time when mankind rose to prominence.
Also, while you are going into your dissertation of bunk, would you please explain to me how it is that your fictional bugaboo, global warming, is going to kill us all and while you are at it, please pay homage to Al Gore who consumes more energy at his house than 232 average American homes in a year, and to the Nobel Society for awarding the largest fraud in the history of the world, and for his Oscar where he did nothing but lie to people so he could pay his damn energy bill.
On second thought, why don’t you just continue to follow the pack that you wrongly believe has all the power, and while you are running with that crowd, you be sure to piss on every form of freedom you find unpalatable, change laws to control every aspect of human behavior, and if that doesn’t work file a lawsuit in the Ninth Circle of Hell, because they will listen to your drivel with a willing ear to erode liberty down to nothing.
But cmb, have you spent enough time at Al Gore’s party so that when you and yours take over, you won’t be cast aside to the bread line with the rest of us? Did you rub enough elbows to get in the good graces of the elite who have done nothing but ruin the scientific process in this country by politicizing it?
by delta18
I hate to have to be the one to point it out but the temperature of photosynthesis was never what scientists were relying on when using oxygen isotopes of tree-rings.
Firstly precipitation isotopic value is dependent on temperature thus the oxygen isotopic value is affected by temperature even before it enters the tree.
Next even if the temperature of photosynthesis is constant the amount of evaporation at the leaf is not and is still dependent on temperature.
So don’t leap to conclusions based on a single paper.
Don’t be shy. We appreciate knowledgeable input.
My understanding of tree physiology is that moisture enters a tree through its roots. Precipitation passes through the ground before entering the tree. Moreover, rain and/or snow falls at a variety of temperatures in any given year (or day, for that matter). And, moisture uptake is also variable throughout the year, hence across a range of temperatures. And, the ambient air temperature varies from microsite to microsite.
So the oxygen isotope ratio in any particular bit of wood is a point measure of a global phenomenon, meaning umpteen millions of samples would be necessary to derive “global” temperature with any degree of accuracy. And if the oxygen (in water) evaporated from the leaf, it would not even be there to measure.
One thing we know for sure is that both conifers and angiosperms evolved under global temperature regimes far warmer than today. The Holocene is an interglacial warm period between Ice Age glaciations that have been occurring like clockwork for about 2 million years. Tree genera are far, far older than that, and during the last 250 million years it has almost always been warmer than now on Planet Earth.
Heck, it was even warmer than now during the last interglacial 120,000 years ago. In fact, it has been warmer than now during almost all of the Holocene, except for the Little Ice Age of 1400-1800. We live in one of the coolest eras of all of Earth history.
Frankly, delta18, a little warming couldn’t hurt. Indeed, warmer is better, for a dozen reasons, not the least of which is that warmer is the normative condition for Life as we know it.
by justhinkin
How about this? Your SUVs and your what-have-you are burning up at a needlessly accelerated rate a finite resource (actually many of them) that should belong to the future as well as the present.
I find it most sad that people are such energy (and everything else) pigs that they will not listen to any reason to be caused to simply put their personal energy into conserving all resources.
And why should you do that? To be kind to all those progeny whom you insist on over-stuffing this poor earth with. If you don’t give a damn about them, put a hat on it so they at least won’t have to, quite so much, spread many fewer resources over a much larger slice of humanity.
You all seem to want to nit pick this and every other issue to death to simply preoccupy yourselves with the meaningless, all the while you screw humanity, literally, into a meaningless oblivion of living as if a sardine with too many can-mates. No one need count or measure tree rings or ice layers to realize that.
My GOD, people, cannot you ONCE peek over your own selfishness and preoccupations and see that this world doesn’t belong to you … it belongs to your children, and theirs. If YOU live and consume like pigs and breed like rabbits, then your children will try to do the same … but in a world left so delicate and so devastated that they will have to occupy all their time just COUNTING the disasters you caused.
Stop over-reproduction and “it’s all for me” consumption and NO one will have to worry so much about the disasters you are causing. Reduce your numbers and reduce our worries. Otherwise you have squandered your “intellect” on your own egocentricity for your “15 minutes” out of human history, and you will, collectively, bear most of the blame for the results (as the most consuming in history).
The search for intelligent life on Earth continues. Prospects so far are not good.
How about this? Hysterical rants, calling people pigs, having a cow about FALSE and HURTFUL MYTHS is not doing your progeny any good, notthinking.
Your apocalyptic presumptions do more harm than good. Inflict your nutty ideas upon yourself — leave the rest of us alone.
by Steve
Does anyone still think GW is true?!!!
I guess a few months makes a big difference what with Climategate, revelations about the Himalayian Glacer melt myth, etc.
I appreciate real scientific work not ideological fanaticism dressed up in scientific clothing.
by delta2
“My understanding of tree physiology is that moisture enters a tree through its roots. Precipitation passes through the ground before entering the tree. Moreover, rain and/or snow falls at a variety of temperatures in any given year (or day, for that matter).”
Yes and thus in northern forests the signal of 18O locked in wood of a tree-ring reflects the average winter temperature (because most of the water in the soil is derived from snow melt.
“And, the ambient air temperature varies from microsite to microsite.”
Correct but this is why researchers use more than one tree and generally from multiple sites to make conclusions. If a study doesn’t do this then you are right to look at it sceptically.
“So the oxygen isotope ratio in any particular bit of wood is a point measure of a global phenomenon, meaning umpteen millions of samples would be necessary to derive “global” temperature with any degree of accuracy.”
Also correct more data points is always good, however, 1. they measure 18O of a specific year derived from the tree-ring not “any bit of wood”. Some studies even look at sub-annual 18O. 2. if you have say hundreds of measurements of sites in different parts of the globe all showing warming then you could start to infer global changes even without having “millions” of points. That doesn’t mean you stop filling those gaps though.
“And if the oxygen (in water) evaporated from the leaf, it would not even be there to measure.”
You show your lack of knowledge of the subject here. delta 18O is the ratio of 16O/18O in a sample. When water evaporates (either from a leaf or lake or soil) the lighter oxygen molecules evaporate first so the 16O evaporates while the 18O is left behind. Thus the water left in the leaf is enriched in 18O and so heavier. That water then gets turned into sugar and then into wood by the tree. The result being more evaporation = more 18O enriched wood and a higher value of delta 18O. It is there to measure just as wood not as water.
“One thing we know for sure is that both conifers and angiosperms evolved under global temperature regimes far warmer than today.”
So using your logic is it good or bad for us that C4 plants (including corn) evolved to cope with low CO2 and that as CO2
Also does this negate their ability to record temperature? Not really.
“The Holocene is an interglacial warm period between Ice Age glaciations that have been occurring like clockwork for about 2 million years.”
The Holocene is only the last 10,000 years. Glaciations have a varied clockwork they were every 41,000 years then switched to every 100,000 years and the most recent ice ages only started ~3 million years ago. However, for the entire Quaternary atmospheric CO2 was between 190 and 280 ppm. Today it is 385 ppm and rising. The last time CO2 was that high was 3.5 million years ago, before the Ice Ages began, when global temperatures were ~5 degrees warmer than today.
“Tree genera are far, far older than that, and during the last 250 million years it has almost always been warmer than now on Planet Earth.”
By this logic is it good or bad that the entire existence of the human race global temperatures have been as warm as, or colder than they are now?
“Frankly, delta18, a little warming couldn’t hurt. Indeed, warmer is better, for a dozen reasons, not the least of which is that warmer is the normative condition for Life as we know it.”
delta18 made no mention of changing temperatures anywhere in his/her post so I find it interesting that you read that into it when he/she was only trying to correct some misconceptions about the specific study mentioned here.
If you have any friends in Miami ask them if they think a little warming (and melting of ice sheets) won’t hurt.
Ask your friends in Missoula if a little more bark beetles and catastrophic wildfire in town wouldn’t hurt. I mean, after all, the Sierra Club and Chad Hanson says “fires are a good thing” so…
There seems to be a problem in these studies with a “control group”. Is there a fudge factor to compensate for today’s increased tree densities, which certainly affects water uptake? I’m certainly not a paleo-botanist but, I would think that such variables would definitely affect the outcome of such studies.
What you haven’t shown is that the new findings actually invalidate the predictions you leap to at the end of your article.
Once you have confirmation that the new findings mean forest dieoffs will not occur, it would be good to add that information so that your article proves its point instead of ending in unproven speculation.