Another Recognized Vegetation Feedback Within The Climate System

Anthony Watts has alerted us to an important new paper which documents another climate feedback. See his post

NASA climate model shows plants slow Global Warming by creating a new negative feedback in response to increased CO2.

The paper is

Bounoua, L., F. G. Hall, P. J. Sellers, A. Kumar, G. J. Collatz, C. J. Tucker, and M. L. Imhoff (2010), Quantifying the negative feedback of vegetation to greenhouse warming: A modeling approach, Geophys. Res. Lett., 37, L23701, doi:10.1029/2010GL045338.

The abstract reads

“Several climate models indicate that in a 2 × CO2 environment, temperature and precipitation would increase and runoff would increase faster than precipitation. These models, however, did not allow the vegetation to increase its leaf density as a response to the physiological effects of increased CO2 and consequent changes in climate. Other assessments included these interactions but did not account for the vegetation down‐regulation to reduce plant’s photosynthetic activity and as such resulted in a weak vegetation negative response. When we combine these interactions in climate simulations with 2 × CO2, the associated increase in precipitation contributes primarily to increase evapotranspiration rather than surface runoff, consistent with observations, and results in an additional cooling effect not fully accounted for in previous simulations with elevated CO2. By accelerating the water cycle, this feedback slows but does not alleviate the projected warming, reducing the land surface warming by 0.6°C. Compared to previous studies, these results imply that long term negative feedback from CO2‐induced increases in vegetation density could reduce temperature following a stabilization of CO2 concentration.”

Excerpts from the conclusions are

“As an additional feedback to water availability caused by CO2‐induced water use efficiency and changes in climate, we postulate that the excess photosynthetic capacity following down‐regulation of the vegetation physiological activity would stimulate vegetation growth much more than previously simulated. When we include these feedbacks in climate simulations with 2 × CO2, the associated increase in precipitation contributes primarily to increase evapotranspiration rather than surface runoff. This results in an additional cooling effect not fully accounted for in previous elevated CO2 climate simulations…….results from this study suggest that long term negative feedbacks from increases in LAI could act to reduce temperature for years following a stabilization of atmospheric CO2 concentration.”

This study reinforces what we found in our papers; e.g. see

Eastman, J.L., M.B. Coughenour, and R.A. Pielke, 2001: The effects of CO2 and landscape change using a coupled plant and meteorological model. Global Change Biology, 7, 797-815.

Our abstract included the findings

“Results indicate that the biological effect of enriched CO2, and of land-use change exhibit dominant effects on regional meteorological and biological fields, which were observed for daily to seasonal time scales and grid to regional spatial scales….Model results highlight the importance of including 2 X CO2 biological effects when simulating possible future changes in regional weather.”

Our other papers on this subject include

Alpert, P., D. Niyogi, R.A. Pielke Sr., J.L. Eastman, Y.K. Xue, and S. Raman, 2006: Evidence for carbon dioxide and moisture interactions from the leaf cell up to global scales: Perspective on human-caused climate change. Global and Planetary Change, Special Issue, 54, 202-208, http://dx.doi.org/10.1016/j.gloplacha.2006.03.015

Marland, G., R.A. Pielke, Sr., M. Apps, R. Avissar, R.A. Betts, K.J. Davis, P.C. Frumhoff, S.T. Jackson, L. Joyce, P. Kauppi, J. Katzenberger, K.G. MacDicken, R. Neilson, J.O. Niles, D. dutta S. Niyogi, R.J. Norby, N. Pena, N. Sampson, and Y. Xue, 2003: The climatic impacts of land surface change and carbon management, and the implications for climate-change mitigation policy. Climate Policy, 3, 149-157.

Narisma, G.T., A.J. Pitman, J. Eastman, I.G. Watterson, R. Pielke Sr., and A. Beltran-Przekurat, 2003: The role of biospheric feedbacks in the simulation of the impact of historical land cover change on the Australian January climate. Geophys. Res. Letts., 30(22), 2168, doi:10.1029/2003GL018261

Pielke Sr., R.A., G. Marland, R.A. Betts, T.N. Chase, J.L. Eastman, J.O. Niles, D. Niyogi, and S. Running, 2002: The influence of land-use change and landscape dynamics on the climate system- relevance to climate change policy beyond the radiative effect of greenhouse gases. Phil. Trans. A. Special Theme Issue, 360, 1705-1719.

While the authors of the Bounoua et al paper was not aware of our earlier studies, I am pleased that the important effect of vegetation dynamics on the climate system continues to be better recognized.

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