Future diversity and lifespan of metazoans under global warming and oxygen depletion

Abstract

The diversification of metazoans began approximately 700–500 million years ago, evolving from cnidarian-like ancestors into complex groups such as arthropods and vertebrates under dynamic environmental conditions. Throughout Earth's history, abrupt climate fluctuations-driven by large-scale volcanism and meteorite impacts-have repeatedly reshaped global biodiversity. Understanding these historical patterns provides critical insights into the long-term future of life under ongoing and future climate change. Here, I model the future ecosystem diversity of terrestrial metazoans-including insects and tetrapods-and marine metazoans by integrating multiple environmental drivers: solar-luminosity–induced warming, alternating icehouse–greenhouse cycles, progressive declines in atmospheric CO2 and O2, abrupt climate fluctuations, and anthropogenic impacts. The results indicate that family-level diversity of terrestrial insects, tetrapods, and marine metazoans-including subterranean and deep-water taxa-will begin to decline approximately 0.5 billion years from now, and ultimately vanish at around 0.9, 0.9, and 1.0 billion years, respectively. These projections hold across models both with and without evolutionary adaptation to extremely low CO2 and O2 conditions. The difference in extinction timing between land and ocean reflects lower maximum temperatures in marine environments. The primary driver of gradual biodiversity loss is the long-term reduction of atmospheric CO2 and O2 due to the steady increase in solar luminosity. However, extinction is completed by episodic warming events-primarily volcanic in origin-that exceed the thermal tolerance limits of metazoans when superimposed on gradual solar-driven warming. These findings offer a unified quantitative framework for understanding the far-future trajectory and ultimate limits of metazoan biodiversity on Earth.