Caldeira Lab Research:Land Plants, Carbon, and Climate

Biogeophysical effects of CO2 fertilization on global climate

G. Bala, K. Caldeira, A. Mirin, M. Wickett, C. Delire, & T.J. Phillips

An investigation of the effects that CO2 fertilization's changes to plant growth have on the global climate. This was done through a comparison of a control model without emissions, and one with specified emissions but that did not include the greenhouse effect. The results indicate that CO2 fertilization has an overall warming effect in the long term.

Bala, G., K. Caldeira, A. Mirin, M. Wickett., C. Delire and T.J. Philips, Biogeophysical effects of CO2 fertilization on global climate. Tellus B 58 (5) 620-627, 2006.

CO2 concentration's effect on temperature without the greenhouse effect: Even when the greenhouse effect is taken out of play, the model showed that CO2 concentration still has a warming effect on the climate. This means that the CO2 fertilization aspect alone would warm the planet.

Decline in surface albedo: CO2 fertilization reduced surface albedo (brightness) by causing a rise of forests and a decline in savannahs and grasslands. Reduced albedo leads to higher temperatures.


CO2 fertilization affects plant growth, which modifies surface physical properties, altering the surface albedo, and fluxes of sensible and latent heat. We investigate how such CO2-fertilization effects on vegetation and surface properties would affect the climate system. Using a global three-dimensional climate-carbon model that simulates vegetation dynamics, we compare two multicentury simulations: a ‘Control’ simulation with no emissions and a ‘Physiol-noGHG’ simulation where physiological changes occur as a result of prescribed CO2 emissions, but where CO2-induced greenhouse warming is not included. In our simulations, CO2 fertilization produces warming; we obtain an annual, and a global-mean warming of about 0.65 K (and land-only warming of 1.4 K) after 430 yr. This century-scale warming is mostly due to a decreased surface albedo associated with the expansion of the Northern Hemisphere boreal forests. On decadal timescales, the CO2 uptake by afforestation should produce a cooling effect that exceeds this albedo-based warming; but if the forests remain in place, the CO2-enhanced greenhouse effect would diminish as the ocean equilibrates with the atmosphere, whereas the albedo effect would persist. Thus, on century timescales, there is the prospect for net warming from CO2 fertilization of the land biosphere. Further study is needed to confirm and better quantify our results.