Caldeira Lab Research:Land Plants, Carbon, and Climate

Quantifying the effects of CO2-fertilized vegetation on future global climate and carbon dynamics

Starley L. Thompson, Bala Govindasamy, Art Mirin, Ken Caldeira, Christine Delire, Jose Milovich, M. Wickett & David Erickson

The effect of atmospheric carbon dioxide on the land biosphere is not completely understood. This question is investigated here through two models: one where CO2 emissions continue vigorously and land uptake continues indefinitely via CO2 fertilization, and another where such fertilization becomes saturated in 2000 and ends early. The results differ greatly, showing that it is currently impossible to determine whether the biosphere's role in carbon uptake will curtail or amplify global warming.

Thompson SL, Govindasamy B, Mirin A, K. Caldeira, C. Delire, J. Milovich, M. Wickett, and D. Erickson. Quantifying the effects of CO2-fertilized vegetation on future global climate and carbon dynamics. Geophysical Research Letters 31 (23): Art. No. L23211 DEC 11 2004

Effect of early saturation on temperature and CO2 concentration: When CO2 fertilization is saturated early, it provokes an increase in temperature and CO2 from situations where fertilization is allowed to continue indefinitely. This change happens because saturation prevents land uptake and causes it to be a source of CO2 by 2050.


Climate and the global carbon cycle are a tightly coupled system where changes in climate affect exchange of atmospheric CO2 with the land biosphere and the ocean, and vice-versa. In particular, the response of the land biosphere to the ongoing increase in atmospheric CO2 is not well understood. To evaluate the approximate upper and lower limits of land carbon uptake, we perform simulations using a comprehensive climate-carbon model. In one case the land biosphere is vigorously fertilized by added CO2 and sequesters carbon throughout the 21st century. In a second case, CO2 fertilization saturates in year 2000; here the land becomes an additional source of CO2 by 2050. The predicted atmospheric CO2 concentration at year 2100 differs by 40% between the two cases. We show that current uncertainties preclude determination of whether the land biosphere will amplify or damp atmospheric CO2 increases by the end of the century.