Seafloor Weathering and Stochastic Outgassing Unlikely to Significantly Shorten the Future Lifespan of Earth's Terrestrial Biosphere

TL;DR

This study models Earth's future biosphere lifespan considering seafloor weathering and stochastic outgassing, finding that these factors can influence but are unlikely to shorten it below 1 billion years, supporting a potentially longer future lifespan.

Contribution

It extends previous climate-weathering models by incorporating seafloor weathering and stochastic outgassing effects to refine estimates of Earth's biosphere longevity.

Findings

Seafloor weathering can shorten biosphere lifespan if it has a strong feedback.

Stochastic outgassing fluctuations impact lifespan if variability exceeds past 1 Gyr.

Weak seafloor weathering and low variability have minor effects.

Abstract

Current understanding suggests that as the Sun brightens in the far future, Earth's carbonate-silicate cycle will offset increasing temperatures by drawing CO$_2$ out of the atmosphere, ultimately leading to the extinction of all terrestrial plant life via either overheating or CO$_2$ starvation. Most previous estimates put the future lifespan of Earth's terrestrial biosphere at $\sim$1 billion yr, but recent work used a new coupled climate-continental weathering model with up-to-date parameter constraints to revise this estimate upward to 1.6-1.86 billion yr. In this study, we extend the model to examine the impacts of seafloor weathering and stochastic variations in CO$_2$ outgassing rates on the remaining lifespan of Earth's terrestrial biosphere. We find that if seafloor weathering has a stronger feedback than continental weathering and accounts for a large portion of global silicate weathering, then the remaining lifespan of the terrestrial biosphere can be shortened, but a lifespan of more than 1 billion yr (Gyr) remains likely. Similarly, stochastic fluctuations in outgassing rates can have a significant impact if the size of the fluctuations exceed those observed over the last 1 billion yr. The impact of weak seafloor weathering and lower variability stochasticity are minor. Our work provisionally supports a lengthened lifespan of Earth's terrestrial biosphere, suggests robustness of this lengthened lifespan to planetary parameters that may vary among exoplanets, and identifies seafloor weathering as a key process that requires further study and constraint.