Uncooling the planet: Rewilding for function in a post-Pleistocene climate

Area of Science:

• Paleoclimatology
• Ecology
• Evolutionary Biology

Background:

• Pleistocene and Holocene epochs shaped ecosystems and human evolution under varying carbon dioxide (CO2) levels.
• The Holocene, often seen as stable, was naturally progressing towards a glacial phase before anthropogenic CO2 emissions altered this trajectory.
• Low CO2 conditions historically supported specific flora and fauna, defined here as low-CO2 dependents.

Purpose of the Study:

• To analyze the impact of rising atmospheric CO2 on ecosystems, particularly African savannas, where Homo sapiens evolved.
• To highlight the threat to biodiversity adapted to open ecosystems due to CO2-driven woody encroachment and reforestation.
• To propose integrating climate-fitness tests with prehistoric analogues for rewilding initiatives.

Main Methods:

• Comparative analysis of Pleistocene and Holocene climate conditions and their ecological impacts.
• Assessment of CO2-driven vegetation changes, specifically woody encroachment in African savannas.
• Review of evolutionary pressures on Homo sapiens and other large mammals during different CO2 regimes.

Main Results:

• Anthropogenic CO2 emissions have reversed the natural trend towards glaciation, preventing a return to cyclic glacial climates for millennia.
• Rising CO2 concentrations exceed the adaptive capacities of many species and ecosystems, accelerating global warming.
• African savannas, historically maintained by fire and carbon scarcity, are experiencing significant woody encroachment due to elevated CO2.

Conclusions:

• The current Holocene baseline is transient; conservation and agriculture must adapt to a dynamic, CO2-driven future.
• Rewilding efforts need to incorporate climate-fitness tests anticipating future CO2 trajectories.
• Systemic policy reforms and local interventions are crucial to address biodiversity loss and ecosystem shifts caused by rapid climate change.