Sol: Destroyer of Worlds
The End of Life on Earth
The Loss of Flora
The current political debate over the influence of anthropogenic CO2 emissions is not without its ironies. One interesting possibility that is not likely to be on the minds of AGW proponants or deniers is that life on Earth may in fact be doomed by catastrophically low levels of CO2! In 1982, Lovelock and Whitfield explored how Earth's atmosphere would react to increased solar luminosity that will impact our planet in the future. They found that warming due to increased luminosity would increase rates of silicate rock weathering, a process which sequesters CO2 into Earth's crust.
It turns out that this decline in CO2 concentrations would likely spell the end of plant life as we know it on Earth. Photosynthesis, the mechanism by which plants utilize the Sun's energy (and in the process create oxygen), requires a certain concentration of CO2 in order to function, much as animal respiration requires a certain amount of oxygen. In Lovelock & Whitfield's model, the atmospheric concentration of CO2 will fall below 150ppm (parts per million) in 100 million years, which will eliminate plants that use solely C3 photosynthesis. Further studies have shown that this threshold will probably not be the end of the biosphere however. C4 pathway photosynthesis can persist to CO2 values as low as 10ppm. Those levels should persist for another 1 to 1.5 billion years. So don't go out and buy that 5mpg SUV to save the planet just yet... we're talking the distant future. This issue is quite distinct from the threat of near term CO2-caused warming!
Past, present, and future biological productivity changes related to CO2 and air temperature. (from Caldeira & Kasting)
Even when plant life is gone, simple life will probably persist on Earth. Biological enhancement of silicate weathering can reduce greenhouse atmospheric warming and extend the time frame in which the Earth is in the habitable zone. In addition, reduction of atmospheric pressure through biotic sequestration of atmospheric nitrogen could possibly extend the lifespan of the modern biosphere further to 2 billion years into the future. Eventually, however, the Sun will win out.
Lovelock, J.E. & Whitfield, M. Nature 296, 561-563 (1982).
Caldeira, K. & Kasting, J.F. Nature 360, 721-723 (1992).
Lenton, T.M. & von Bloh, W. GRL 28, 1715-1718 (2001).
Li, K., Pahlevan, K., Kirschvink, J.L. & Yung, Y.L. PNAS 106, 9576-9579 (2009).<< An Evolving Star Home The Desert Planet >>
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