Soil Carbon Dioxide Planetary Thermostat.

Abstract

Biological regulation of planetary temperature has been explained with the Daisyworld model, in which reflective-cooling white daises balance absorbing-warming black daisies. This article advances the proposition that cooling "daisies" of Daisyworld represent carbon sequestration and consumption by productive soils and ecosystems, such as grasslands expanding into deserts and tropical forests migrating toward the poles. On the other hand, warming "daisies" represent continued CO2 emissions from volcanoes and springs allowed by unproductive frigid and desert ecosystems. Greenhouse spikes of CO2 in deep time from large perturbations, such as flood basalt eruptions and asteroid impacts, did not continue as lethal runaway greenhouses, such as Venus, nor did low CO2 of ice ages decline to a sterile global snowball, such as Mars. These hypotheses are quantified and tested by new global soil maps derived from paleosols of the last extremes of atmospheric CO2: middle Miocene (16 Ma) and last glacial maximum (20 ka), when CO2 levels were 588 ± 72 and 180 ppm, respectively. Observed expansion of productive soils curbed large atmospheric injections of CO2 in deep time and observed expansion of unproductive soils during ice ages of low CO2 was thwarted by continued metamorphic and volcanic degassing. This short-term Soilworld thermostat of biogeographic redistribution of ecosystems supplemented long-term evolution of terrestrial carbon sequestration curbing solar radiation increases over billions of years. Similar agricultural management of ecosystems has potential for short-term carbon sequestration.