Naik, V., C Delire, and D.J. Wuebbles (2004). Sensitivity of global biogenic isoprenoid emissions to climate variability and atmospheric CO2. Journal of Geophysical Research 109(D6), D06301, 10.1029/2003JD004236

Abstract:

Various geoengineering schemes have been proposed to counteract anthropogenically-induced climate change. Govindaswamy and Caldeira (2000) suggest that a 1.8% reduction in solar radiation incident on the Earth’s surface could noticeably reduce regional and seasonal climate change from increased atmospheric carbon dioxide (CO2). However, response of the terrestrial biosphere to reduced solar radiation in a CO2–rich climate was not explored. Atmospheric CO2 and incident solar radiation are critical for photosynthesis. Elevated CO2 in the atmosphere stimulates photosynthesis resulting in increased primary production of terrestrial ecosystems. In contrast, diminished irradiance limits photosynthesis and therefore, net carbon gain and plant growth. In this study, we used a dynamic global ecosystem model, Integrated Biosphere Simulator (IBIS), to investigate if reduced solar luminosity diminished the productivity of terrestrial ecosystems. Our analyses illustrated that there were spatial variations in the response of the terrestrial biosphere to engineered solar radiation because of complex interactions with the hydrologic cycle. While productivity decreased by less than 2% in the tropical and boreal forests as hypothesized, it increased by a similar percentage in the temperate deciduous forests and grasslands. This increase in productivity was attributed to a ~1% reduction in evapotranspiration in the Geoengineered scenario. Our initial hypothesis was rejected because of unanticipated effects of engineered solar radiation on the hydrologic cycle. However, any geoengineering approaches that reduce solar luminosity at the Earth’s surface need to be thoroughly analyzed in view of the implications on ecosystem productivity and the hydrologic cycle in addition to ethical and political reasons.