TCS Daily

Tree Haze and Cool Days?

By Robert C. Balling - September 12, 2003 12:00 AM

Record temperatures in Europe have the greenhouse crusade whipped-up in a frenzy about global warming. As Europeans and North Americans leave their hot, crazy cities and seek some cooler weather in the lazy countryside, they encounter the hazy days of summer.


Much of the haze comes from trees that emit a phenomenal number and total volume of hydrocarbons into the atmosphere. The dinosaurs saw the haze, Columbus saw the haze, and if you venture into the countryside, you will see the haze. The plant vapors are the topic of an interesting article that recently appeared in the prestigious Journal of Geophysical Research.


A team of scientists from Canada and the University of Virginia measured phytogenic aerosols over a forested area in eastern Canada. At times, the Barr et al. team found the concentration of these particles to be above 5,000 particles per cubic centimeter. Furthermore, they reported that these naturally occurring particles "generated substantial attenuation of the incoming solar irradiance stream." They concluded that "this negative radiative influence could offset substantial fractions of the regional thermal forcing resulting from increased levels of greenhouse gases such as carbon dioxide. It is concluded that greater radiative influences (cooling) could be present over regions dominated by hydrocarbon productive forest ecosystems."


The vapors have another effect that could help slow down any global warming -- they likely produce more clouds. In 1998, a group of scientists studied a Eucalyptus forest in Portugal and the Kavouras et al. team found that gases produced by the trees were converted into particles that were perfectly suited as cloud condensation nuclei. Similarly, another team of scientists recently studied particles emitted by a boreal forest in Finland and organic cloud-droplets above the forest. O'Dowd et al. concluded that these particles may "affect climate by acting as nuclei for cloud condensation."


But the good news for the future is that trees all over the planet grow even faster and bigger given elevated levels of atmosphere CO2. In one recent week alone, two articles appeared in the professional literature reinforcing that ongoing lesson. In the first study, a team of scientists from the United States, Italy, and England grew poplar trees outdoors with ambient (370 ppm) and elevated (550 ppm) atmospheric CO2 concentrations. Bernacchi et al. concluded that "A 50% increase in [CO2] under these open-air field conditions resulted in a large and sustained increase in" light saturated photosynthesis. They developed a method for calculating total daily integrated photosynthesis and found up to an 86.5 percent increase given the higher levels of CO2. In the second article, a team of scientists from Finland grew 15-year-old Scots opine trees in various combinations of ambient and elevated temperature (AT and ET) and ambient and elevated atmospheric CO2 concentrations (AC and EC). Kilpeläinen et al. concluded that, "Absolute radial growth over the 3-year period was 54% greater in AT+EC trees and 30 and 25% greater in ET+AC and ET+EC trees, respectively, than in AT+AC trees."


The bigger trees and the more widespread forests of the future will produce astronomical amounts of organic compounds that will help cool the Earth by reducing solar radiation and increasing cloudiness. Mother Nature is no idiot, and the biosphere may be clever enough to stop any harmful global warming related to activities of the planet's most intelligent creatures. Those lazy, crazy, hazy days of summer may be critical in controlling the temperature of the Earth.



Barr, J.G., J.D. Fuentes, and J.W. Bottenheim. 2003. Radiative forcing of phytogenic aerosols. Journal of Geophysical Research, 108, 10.1029/2002JD002978.


Bernacchi, C.J., C. Calfapietra, P.A. Davey, V.E. Wittig, G.E. Scarascia-Mugnozza, C.A. Raines, S.P. Long. 2003. Photosynthesis and stomatal conductance responses of poplars to free-air CO2 enrichment (PopFACE) during the first growth cycle and immediately following coppice. New Phytologist; 159, 609-621.


Kavouras, I.G., Mihalopoulos, N. and Stephanou, E.G. 1998. Formation of atmospheric particles from organic acids produced by forests. Nature, 395, 683-686.


Kilpeläinen, A., H. Peltola, A. Ryyppö, K. Sauvala, K. Laitinen, and S. Kellomäki. 2003. Wood properties of Scots pines (Pinus sylvestris) grown at elevated temperature and carbon dioxide concentration. Tree Physiology, 23, 889-897.


O'Dowd, C.D., Aalto, P., Hameri, K., Kulmala, M. and Hoffmann, T. 2002. Atmospheric particles from organic vapours. Nature, 416, 497-498.


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