Pliocene and Eocene provide best analogs for near-future climates

Area of Science:

• Paleoclimatology and Climate Modeling
• Earth System Science
• Climate Change Adaptation

Background:

• Global warming is driving Earth's climate toward unprecedented states.
• Past geological climate states can serve as analogs for future warming.
• Societal adaptation is challenged by these novel climate trajectories.

Purpose of the Study:

• To quantitatively compare projected future climate states with six geohistorical climate benchmarks.
• To assess the emergence of geologically novel climates under different emission scenarios.
• To evaluate the potential for climate system reversion to past states.

Main Methods:

• Utilized simulations from three Earth system models: HadCM3, GISS Model E2-R, and CCSM (v3 & v4).
• Analyzed climate states under Representative Concentration Pathway 4.5 (RCP4.5) and RCP8.5 scenarios.
• Quantitatively assessed similarity between future projections and geohistorical analogs (Eocene, Pliocene, etc.).

Main Results:

• Under RCP8.5, future climates resemble Mid-Pliocene conditions by 2030 CE and Eocene conditions by 2150 CE.
• RCP4.5 stabilizes climate at Pliocene-like conditions by 2040 CE, with novel climates affecting <1% of the globe.
• RCP8.5 leads to novel climates across 8.7% of the globe, characterized by extreme temperatures and precipitation.

Conclusions:

• Stabilizing emissions at RCP4.5 levels may allow climate to reach Pliocene-like conditions.
• Unmitigated emissions (RCP8.5) risk reversing millions of years of cooling rapidly, potentially exceeding adaptive capacity.
• The emergence of novel and rapidly reverting climates poses significant challenges for evolutionary and societal adaptation.