The Impact of Life on Climate Stabilization Over Different Timescales

Surface life has been argued to be crucial in keeping a planet habitable in the long term. Biologically enhanced weathering compensates for increasing solar luminosity, and temperature-dependent plant productivity weakens climate perturbations. Furthermore, a reduced calcification rate of marine organisms provides a negative feedback to rising atmospheric CO₂. Here, I present a model of the long-term carbon cycle including biological enhancement of weathering and marine calcification. Climate oscillations of periods from thousands to millions of years arise from a simple model of mountain uplift and erosion. I systematically study the influence of the biologically driven feedbacks on damping these oscillations. For oscillations of periods <2 Myr, the marine calcification feedback yields surface temperature amplitudes that are approximately 1/3 lower compared to a model that ignores this feedback. Abiotic oceans, however, would not necessarily imply a less stable climate on short timescales, due to a higher pH and thereby a higher buffer capacity. On longer timescales, the higher ocean pH would reduce climate stability, since the seafloor weathering feedback would work less efficiently. Biological enhancement of weathering helps stabilizing the climate against oscillations of periods >0.5 Myr. These findings are sensitive to the ratio of land to oceans, however. Furthermore, the mantle carbon degassing rate plays a role, since the temperature dependence of biological primary productivity may be smaller at higher temperatures. Altogether, life can be argued to stabilize the climate on timescales longer than some 100 kyr, while details depend on the geological state of the planet.