Future climate forcing potentially without precedent in the last 420 million years

TLDR

Earth’s climate over geological timescales is mainly driven by changes in total solar irradiance and atmospheric greenhouse gas concentrations. We find that the ~50 W m⁻² increase in total solar irradiance over the last ~420 Myr was largely offset by a long‑term decline in CO₂, likely due to silicate weathering and land‑plant expansion, but future fossil‑fuel‑driven CO₂ rises could produce radiative forcing and Earth‑system responses unprecedented in the last half‑billion years.

Abstract

Abstract The evolution of Earth’s climate on geological timescales is largely driven by variations in the magnitude of total solar irradiance (TSI) and changes in the greenhouse gas content of the atmosphere. Here we show that the slow ∼50 Wm −2 increase in TSI over the last ∼420 million years (an increase of ∼9 Wm −2 of radiative forcing) was almost completely negated by a long-term decline in atmospheric CO 2 . This was likely due to the silicate weathering-negative feedback and the expansion of land plants that together ensured Earth’s long-term habitability. Humanity’s fossil-fuel use, if unabated, risks taking us, by the middle of the twenty-first century, to values of CO 2 not seen since the early Eocene (50 million years ago). If CO 2 continues to rise further into the twenty-third century, then the associated large increase in radiative forcing, and how the Earth system would respond, would likely be without geological precedent in the last half a billion years.