Caldeira Lab Research:Ocean acidification and ocean carbon cycle

Forests, climate, and silicate rock weathering

K. Caldeira

Carbonate–silicate cycle models have helped us to gain a quantitative understanding of the potential impacts of a wide range of factors on the long-term global carbon cycle. Here we investigate how to represent these factors in carbonate-silicate cycle models.

Caldeira, K., Forests, climate, and silicate rock weathering. Journal of Geochemical Exploration 88 (1-3) 419-422 Special Issue, 2006.

Figure 1: Atmospheric CO2 content (relative to pre-industrial) (a) and temperature change (K) (b) as a function of the bclimate feedback factorQ in the GEOCARB III model for the present day and 300 Ma. (The 300 Ma results reduce solar intensity, but all other factors are as for today.) The thick solid line is the result for the GEOCARB III model (Berner and Kothavala, 2001). The thin solid line adds the direct warming effect of CO2-fertilization using the linear Eq. (2). The thin dashed line adds the effect using the Michaelis-Menten equation described by Eq. (4). Consideration of direct warming induced by CO2-fertilization of vegetation affects atmospheric CO2 predictions, but has little impact on predicted temperatures.


Over time periods of 10^6 years and longer, atmospheric carbon dioxide content is largely controlled by a balance between silicate rock weathering and CO2 sources (degassing from the Earth plus net organic carbon oxidation). Vegetation cover can affect silicate rock weathering rates by increasing soil CO2 content, stabilizing soil cover, and producing organic acids. Forests absorb more solar radiation than most other ecosystems; this tends to warm Earth's climate, especially outside of the tropics; this warmth would tend to increase silicate rock weathering rates. Here, we develop preliminary parameterizations of this effect that could be incorporated into carbonate–silicate cycle models, based on the results of general circulation model simulations.