Alkalinity responses to climate warming destabilise the Earth's thermostat

Alkalinity generation from rock weathering modulates Earth’s climate on geological timescales. Although lithology is often considered the dominant control on global alkalinity generation, other first-order controls are less clear, particularly disentangling climatic versus erosional influences. Using global river observations paired with in situ 10Be-derived erosion rates across multiple climate zones, the study identifies erosion rate as a first-order control on riverine alkalinity, alongside areal carbonate proportion, mean annual temperature (MAT), catchment area, and soil regolith thickness. A generalized linear model reveals an “efficient erosion rate regime” (~10–1000 mm ka⁻¹) that maximizes alkalinity, with peaks near ~100 mm ka⁻¹, and shows optimal MAT for alkalinity in temperate climates (~7.5–15 °C). Projections indicate substantial changes in weathering fluxes under climate warming by 2100: mid-latitude alkalinity fluxes may decrease under a low-emissions scenario (SSP1-2.6) but increase under a high-emissions scenario (SSP5-8.5), with regional changes up to 68% depending on conditions. These alterations imply a rapid feedback of ocean CO₂ sequestration to climate.

Nele Lehmann, Tobias Stacke, Sebastian Lehmann, Hugues Lantuit, John Gosse, Chantal Mears, Jens Hartmann, Helmuth Thomas