Dendroclimatology: thermometer or hygrometer?
Hot climate or cold, tree leaves stay in comfort zone
From the Google Climate Discussion Group, see an article also in Science News
Paris, June 11; Agence France-Presse
A new study that shows their internal temperature remains constant at 21.4deg could challenge the way trees are used to determine historical climate data
The internal temperature of leaves, whether in the tropics or a cold-clime forest, tends toward a nearly constant 21.4 degrees Celsius, reports a study released today.
It had long been assumed that actively photosynthesising leaves – using energy from sunlight to convert carbon dioxide and water into sugar – are nearly as cold or hot as the air around them.
The new findings not only challenge long-held precepts in plant biology, but could upend climate models that use tree rings to infer or predict past and present temperature changes.
For decades, scientists studying the impact of global warming have measured the oxygen isotope ratio in tree-rings to determine the air temperature and relative humidity of historical climates.
Oxygen atoms within water molecules evaporate more or less quickly depending on the number of neutrons they carry, and the ratio between these differently weighted atoms in tree trunk rings has been used as a measure of year-to-year fluctuations in temperatures and rainfall.
“The assumption in all of these studies was that tree leaf temperatures were equal to ambient temperatures,” lead researcher Brent Helliker told AFP. “It turns out that they are not.”
Helliker and University of Pennsylvania colleague Suzanna Richter turned those assumptions upside down in examining 39 tree species, across 50 degrees of latitude ranging from sub-tropical Columbia to boreal Canada.
They compared current observed records of humidity and temperature against the isotope ratios in the trees, and found that tree leaves were internally cooler than surrounding air temperatures in warm climes, and warmer in cool climes.
Even more startling was that in all cases the average temperature – over the course of a growing season – was about 21degC.
“It is not surprising to think that a polar bear in northern Canada and a black bear in Florida have the same internal body temperature,” because both animals have internal thermostats to prevent overheating or freezing to death, he said.
“But to think that a Canadian black spruce and a Caribbean Pine have the same average leaf temperature is quite astonishing,” he added.
Tree leaves keep cool through constant evaporation and reducing sun exposure through leaf angles or reflective qualities. Warmth is gained by decreasing evaporation and increasing the number of leaves per branch.
All these tricks should be seen as evolutionary adaptations that help the trees attain a maximum of nutrients through optimal photosynthesis, Helliker said.
The fact that part of this adaptation occurs at the level of entire forest canopies, and not just within individual leaves, is one reason direct measurements of tree temperatures have been so hard.
The new findings, published in the British journal Nature, are bolstered by a recent study of a mixed species forest in Switzerland based on infrared thermal imaging.
Measured across an entire growing season, the forest canopy temperatures were found to be 4degC to 5degC higher than the cool, ambient air in the Swiss Alps.
AFPar 12/06/08 08-05NZ
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I never thought about it before, but I suppose it isn’t that surprising given that humans have a relatively constant internal temperature despite geographical location.
How annoying! Is there no end to what we don’t know?
Trees are “warm-blooded”? Who’da thought?
WOW!!!
Just WOW!!!
I wonder how Gavin and Hansen will respond to this? If this avg temp efficiency turns out to be case for the trunk as well as the leaves (would also provide another mechanism for trees to resist freezing in the winter), it would certainly explain the “Hokey” Stick’s stick.
Ouch! There is just bad news every day for the alarmists. I have always thought tree rings were a better indication of moisture than temperature anyway.
Has ring width as a proxy for temperature never been benchmarked?
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Good to see someone still kicking the tires on this used model to see if they still hold good pressure. By all appearances they may be going flat.
Not to be a defender of tree ring climatology, but isn’t analysis of tree ring widths, not oxygen isotope ratios, the primary methodology relied on to produce the now discredited hockey sticks?
This is an astonishing discovery and illustrates how things that appear to be self evident quite often aren’t.
Also this discovery could have been made by anyone with an infrared camera. How many infrared pictures of trees have been taken and no one noticed that leaves were always the same color.
Or, they could have just asked any kid why he climbed up in his favorite tree in the summer.
That’s a great piece of information — truly non-intuitive, but it does makes sense when you think that work is being performed. Plants having a thermostatic mechanism; what concept. This just shows you how robust Nature is. Thanks for pointing it out. By the way, I am an avid gardener and I now see C02 as a fertilizer for plants; I don’t want C02 cuts: the biosphere seems to thrive — as you pointed in a previous post. Feed the plants! Keep the C02 coming.
I just assumed someone had already audited this basic feature of the proxy for temperatures.
Has someone bothered checking today’s tree rings versus temperature?
It’s amazing what gets overlooked in today’s world of science and politics.
The ring width to temperature relationship has always been based on an assumption. Its the manniacs of AGW that forgot about the problem with assumptions.
They found a curious statistical signal in the tree ring data that they thought allowed them to crow to the world that late 20th century warming was unprecedented.
It turns out that only thing that was unprecedented was their procedure, which either through naivety (ignorance) or malfeasance (possible but not likely) gave them the “smoking gun” the activists needed to raise the climate alarm.
I find it amazing that the hockey stick is still in use. I attended a public meeting just last March where a county official used it as part of a presentation on climate change in the PNW.
After the meeting I privately explained the facts. He hasn’t used it since, but the county remains stuck on stupid regarding AGW (this is the Seattle area).
Heh!
Another stab at the Hockey Stick.
Somewhere in the wooly wilds of Ontario, Steve McIntyre is smiling. I hope. It’s a gorgeous day today.
Oh heck.
Another inconvenient truth.
Didn’t these people get the message about what kind of results they were to come up with?
Just goes to show you what happens when real scientists actually study something and an assumption turns and bites the fashionably chic True Believers on their backsides.
Okay, enough venting. This is the sort of inquiry I always expect from science but too often am disappointed, most especially from the area of climatology.
The following is my own understanding, always open to new and improved insite:
Nutrients, light, and moisture. The big three.
Moisture: Tree rings demonstrate varying amounts of these essential ingredients. Note that a hot, dry, desert blooms infrequently, not because of temperature changes, but because it rains.
Temperature: Some plants withstand a great deal of temperature ranges, others are temp specific. Wine grapes in the PNW are an example of temp specific plant. GW encouraged growers to switch from temp insensitive orchards (like many kinds of plum, apple and cherry trees) to the glam of wine grapes. Hot dry summers in the inland NW prompted farmers to stop planting peas. The wine grower will have a much bigger downfall than the pea grower will. Interesting side note: Initial grape growers came from California. Pea farmers have ALWAYS been here. Pea fields have not been turned into grape fields. Orchards have. Not smart.
Nutrients: Bat poop makes the best fertilizer! Plus you can use it for gun powder when gas goes to $6.00 a gallon.
Does this represent another negative feedback mechanism to increasing temperatures from CO2? More atmospheric CO2 causes more plant growth – shouldn’t a global increase of plant matter at this constant temperature tend to pull the atmospheric temperature towards 21.4C?
Light: Some plants bloom at night, some during the day, some in shade, and some only in full sun. Some even bloom in spite of smog. Most plants show a preference for the sun. They bend towards the light in order to maximum benefit. Plants seem to have figured it all out. Without Gore. For me, I would like to say that I am at least as smart as a plant. Gore seems to have not risen to that level yet.
“For me, I would like to say that I am at least as smart as a plant.” Pam
“Pride goeth before a fall…” Proverbs
Why do I pick on Pam?
She makes it easy
and thus I can.
Plus her head, though not too green,
has quite a bit of red instead.
“shouldn’t a global increase of plant matter at this constant temperature tend to pull the atmospheric temperature towards 21.4C?”
Probably not. If the tree removes heat from it’s leaves it has to put that heat somewhere else, perhaps it dissipates the heat into the soil via the roots.
Terry,
I’ve been to the woolly wilds of Ontario. Steve lives about 300 km (200 mi) south of there in Toronto, a major urban centre (notice Canadian spelling) with over 3 million souls.
I’ll be up there again this summer (late July). Hoping that warming occurs before I get there. Black flies are nasty in cold summers. The summer of 1982 was one such year. I was working in central Labrador and nearly went nuts from the black flies.
I think that there was an article on rings vs temp on here a while back. The conclusion seemed to be that tree ring size was more related to moisture, as long as the temperature was withing the plants ‘acceptable’ range.
Philip_B (09:00:46) :
Maybe it’s because a typical IR photo looks like B&W. The ones that map IR to visible color are relatively recent and usually expensive. Here are more. The colors appearing in some of these were likely added using post-processing
DAV,
Actually, it is more likely because the kind of IR photograph that is commonplace is using “near-IR”, that is wavelengths just barely longer than visible red light. Temperature measurement with IR requires sensitivity to “far-IR” or much longer wavelengths. It is much more difficult to take meaningful photographs with far IR light. Until fairly recently, commercial cameras that could do this were tied up in military applications. FLIR is one of the primary patent holders, and their name reveals their military/aerospace origins.
At least part of the problem is that the sensor has to be carefully temperature controlled itself, or self heating distorts the image.
Also, one has to find materials that are transparent in the far IR range with which to construct the optics. I know that one material that works well is a KCl crystal, but it has problems with being both fragile and soluble in water. I am sure that the optical path in Anthony’s FLIR camera is not made of KCl…
Other than the absolutely astonishing and fascinating finding, I’m not sure what this will actually affect in the record, nor which way it will go. But it does bring into question yet again our understanding of the historical temp record.
Within the last few thousand years, were temps more or less variable than we thought? The warmists tend to say they were less variable, the skeptics more. And with the discovery (not quite the right word) that the sun’s irradiance varies less than thought, our entire understanding of this history is clouded. With all this new research going on, we know less than we ‘knew’ before.