Alkalinity responses to climate warming destabilise the Earth's thermostat

Alkalinity generation from rock weathering modulates Earth's climate at geological time scales. Although lithology is thought to dominantly control alkalinity generation globally, the role of other first-order controls appears elusive. Particularly challenging remains the discrimination of climatic and erosional influences. Based on global observations, here we uncover the role of erosion rate in governing riverine alkalinity, accompanied by areal proportion of carbonate, mean annual temperature, catchment area, and soil regolith thickness. We show that the weathering flux to the ocean will be significantly altered by climate warming as early as 2100, by up to 68% depending on the environmental conditions, constituting a sudden feedback of ocean CO2 sequestration to climate. Interestingly, warming under a low-emissions scenario will reduce terrestrial alkalinity flux from mid-latitudes (-1.6 t(bicarbonate) a(-1) km(-2)) until the end of the century, resulting in a reduction in CO2 sequestration, but an increase (+0.5 t(bicarbonate) a(-1) km(-2)) from mid-latitudes is likely under a high-emissions scenario, yielding an additional CO2 sink. The weathering alkalinity flux from mid-latitudes to the ocean will be strongly altered by climate warming by 2100. Under different emissions scenarios either a strengthening or a weakening of the flux and thus of the oceanic CO2 buffer is predicted.

Automated summary

Alkalinity generation from rock weathering has a significant impact on Earth's climate on geological time scales. This study finds that erosion rate plays a crucial role in determining riverine alkalinity, along with carbonate proportion, mean annual temperature, catchment area, and soil regolith thickness. Climate warming will significantly alter the weathering flux to the ocean by 2100, with the potential for a strengthening or weakening effect on the oceanic CO2 buffer, depending on emissions scenarios.