Evapotranspiration

Here is an email exchange between me and Dr. Caldeira of Stanford. His responses are highlighted in yellow.

On Wed, May 5, 2010 at 2:29 PM, Wit's End <witsendnj@yahoo.com> wrote:

Dear Dr. Caldeira and Dr. Cao, I am writing in reference to your research as described in this Science Daily article. I have a couple of questions for you. The first regards the denier canard that "CO2 is food for trees." I have likened that to claims that the American diet rich in calories is beneficial for health, which is of course preposterous.

Yes, CO2 in general is good for trees at is allows them to use water more efficiently.

Aside from that though, I have read that naturally occurring CO2 and the CO2 released from burning fuels have a different isotope. So my first question is, is anyone investigating whether the fuel-emitted CO2 is actually food for plants, or could plants react to it differently because it is actually not quite the same?

Yes, this is being widely investigated. Plants can use fossil fuel CO2 just as well as regular CO2 (actually, just a tiny bit better because C12 diffuses faster than C13).

My other question is specific to your study. I have noticed that trees up and down the east coast of the US are in rapidly accelerating decline. In fact, there are reports from many locations around the world that trees are dying at an unprecedented rate. Foresters and others connected to the lumber industry almost universally attribute this to species-specific insects, bacteria, or fungus. Some acknowledge that climate change warming and drought plays a role. However, I believe the dying of trees is so widespread it cannot be explained by a sudden virulence of all sorts of pests. It cannot be primarily due to drought because young trees that are being watered in nurseries, and last year even decorative plants in pots as well as aquatic plants like lotus and waterlilies, exhibited the identical symptoms of exposure to toxic greenhouse gas emissions. Ozone is well known to damage the stomata of foliage, interfering with the ability to photosynthesize and produce chlorophyll. Since the background level of tropospheric ozone is inexorably rising, and traveling large distances from its point of origin, it seems likely to be the primary cause for trees to be dying. I have also considered the recent emissions of volatile organic compounds from ethanol, and the addition of nitrogen to gasoline. When I first became interested in this problem about two years ago I asked several scientists whether rising CO2 could in and of itself harm trees and I was told this was impossible.

I agree. CO2 is not harming trees but the climate effects of CO2 might harm trees. Another factor to consider is that humans are helping transport pathogens in a way this his historically unprecedented.

Your research indicating trees lose water as levels increase has made me wonder anew what role CO2 might play. Already this spring the leaves up and down the east coast are actually hanging limply, wilted, on the trees. They are smaller than normal, thin and transparent. Do you think this could this be a consequence of too much CO2, or would it be more like ozone? Whatever the precise mechanism, to me it is quite obvious from empirical evidence that our terrestrial ecosystem based on trees is collapsing, just as plainly as the coral reefs are bleaching in the oceans. It's ridiculous that the subject is virtually taboo, thus ensuring nothing will be done about it until we have no more fruit, nuts, wood, shade, habitat, or maple syrup. And of course already a critically important carbon sink is now a net emitter as the trees have stopped growing and instead are dropping branches. They only prayer we have to save the forests (and ourselves) is to stop burning fuel and switch to clean, renewable energy. If that means we all have to conserve and stop flying for holidays, so what? It's better than starving to death. I wish some scientists with authority would tackle this issue and raise the alarm with the public and the politicians.

Again, CO2 is not harming trees but the climate effects of CO2 might harm trees. I believe that transport of pathogens by humans could be presenting many organisms with unprecedented challenges

Look at humans -- we now have AIDS, West Nile Virus, etc, etc. as a result of an unprecedented change in global transportation systems.

I have been posting photographs and links to research at www.witsendnj.blogspot.com, if you're interested. Please feel free to ask any questions and thank you for reading. Sincerely, Gail Zawacki Oldwick, NJ

And yet in this article from Science Daily, the FACE project reports that in experiments in the real world, rising CO2 means crop yield is decreased by 50%! It was very nice of Dr. Caldeira to answer my questions, but with all due respect, I don't see how such a profound difference in the evapotranspiration of foliage - significant enough to warm the surface of the earth - can NOT have some corollated impact on the vegetation.

For instance, if humans lost 50% of the ability to sweat, what would happen to us in the heat?

I think perhaps Dr. Caldeira is more concerned about the warming effect on the climate than the impact on plants. He did not even address the potential of damage from ozone, although that is not in the scope of his study.

His observation about traveling pathogens is important of course. We have only to think of Dutch Elm disease, and smallpox brought to America by the Europeans. However in even more instances of species collapse, it isn't an introduced foreign disease but a native disease that has exploded for unknown reasons. Following are several links to studies about the effects of ozone on vegetation, one of which is to increase vulnerability to insects, disease, and fungi.

Here is an illuminating article in Science Daily from research published in 2007, indicating that ozone reduces crop yield, and this article in Science Daily from December 2008 says that tree growth is being reduced:

"Ozone is the third strongest greenhouse gas, directly contributing to global warming, and is the air pollutant considered to be the most damaging to plants. But more importantly, it has the potential to leave more carbon dioxide, ranked as the first strongest greenhouse gas, in the atmosphere by decreasing carbon assimilation in trees. Ozone pollution occurs when nitrogen oxides have a photochemical reaction with volatile organic compounds.

“This research quantifies the mean response of trees to ozone pollution measured in terms of total tree biomass, and all component parts such as leaf, root and shoot, lost due to ozone pollution,” said Dr. Victoria Wittig, lead author of the study. “Looking at how ozone pollution affects trees is important because of the indirect impact on carbon dioxide concentrations in the atmosphere which will further enhance global warming, in addition to ozone’s already potent direct impact.”

In addition to ozone pollution reducing the strength of trees to hold carbon in the northern temperate mid-latitudes by reducing tree growth, the research also indicates that broad-leaf trees, such as poplars, are more sensitive to ozone pollution than conifers, such as pines, and that root growth is suppressed more than aboveground growth.

“Beyond the consequences for global warming, the study also infers that in mixed forests conifers will be favored over broad-leaved trees, and that the decrease in root size will increase the vulnerability to storms,” said Wittig."

Has anyone noticed all the trees falling down and power outages lately?

While this related article Manning of Amherst reports that ozone is reducing the yield of important crops such as wheat and soy, contributing to world hunger.

“Plants are much more sensitive to ozone than people, and a slight increase in exposure can have a large impact on their productivity,” says Manning, a professor of plant, soil and insect sciences. “The new ozone standard set by the U.S. EPA in March 2008 is based on protecting human health, and may not be strict enough to protect plants.” Manning served on the Clean Air Science Advisory Committee for the EPA in 1997 when the previous air quality standard for ozone was developed.

According to Manning, emission controls on cars have been successful in reducing short periods of high ozone levels called peaks, but average concentrations of ozone in the atmosphere throughout the year, called the background level, is increasing as polluted air masses from Asia travel to the U. S. and then on to Europe. Background levels are now between 20 and 45 parts per billion in Europe and the United States, and are expected to increase to between 42 and 84 parts per billion by 2100.

Apparently the New Zealanders are fearful that a fungus will wipe out their giant kauri trees (found at the website TakeCover.) It isn't clear from the article if it is an introduced fungus, or indigenous. I will attempt to find out. Either way, it's very very sad. I would love to see a tree that big. There is a person in this photo, who is dwarfed!