Pliocene and Eocene provide best analogs for near-future climates

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 115; no. 52; pp. 13288 - 13293
• Main Authors: Burke, K. D., Williams, J. W., Chandler, M. A., Haywood, A. M., Lunt, D. J., Otto-Bliesner, B. L.
• Format: Journal Article
• Language: English
• Published: Goddard Space Flight Center National Academy of Sciences 26.12.2018
• Subjects: Benchmarks; Biological Sciences; Climate; Climate change; Climate models; Climate system; Computer simulation; Earth; Earth science; Ecosystem; Emission; Eocene; Greenhouse effect; Greenhouse gases; High temperature; Holocene; Meteorology And Climatology; Models, Theoretical; Paleoclimate science; Paleontology; Physical Sciences; Planetary boundary layer; Pliocene; Precipitation; Rainfall; Reversion; Temperature; Paleoclimate; Climate Analog; Climate Change; No Analog; Planetary Boundary; no analog; climate analog; planetary boundary; paleoclimate; climate change
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1809600115

As the world warms due to rising greenhouse gas concentrations, the Earth systemmoves toward climate states without societal precedent, challenging adaptation. Past Earth system states offer possible model systems for the warming world of the coming decades. These include the climate states of the Early Eocene (ca. 50 Ma), the Mid-Pliocene (3.3–3.0 Ma), the Last Interglacial (129–116 ka), the Mid-Holocene (6 ka), preindustrial (ca. 1850 CE), and the 20th century. Here, we quantitatively assess the similarity of future projected climate states to these six geohistorical benchmarks using simulations from the Hadley Centre Coupled Model Version 3 (HadCM3), the Goddard Institute for Space Studies Model E2-R (GISS), and the Community Climate System Model, Versions 3 and 4 (CCSM) Earth system models. Under the Representative Concentration Pathway 8.5 (RCP8.5) emission scenario, by 2030 CE, future climates most closely resemble Mid-Pliocene climates, and by 2150 CE, they most closely resemble Eocene climates. Under RCP4.5, climate stabilizes at Pliocene-like conditions by 2040 CE. Pliocene-like and Eocene-like climates emerge first in continental interiors and then expand outward. Geologically novel climates are uncommon in RCP4.5 (<1%) but reach 8.7% of the globe under RCP8.5, characterized by high temperatures and precipitation. Hence, RCP4.5 is roughly equivalent to stabilizing at Pliocene-like climates, while unmitigated emission trajectories, such as RCP8.5, are similar to reversing millions of years of long-term cooling on the scale of a few human generations. Both the emergence of geologically novel climates and the rapid reversion to Eocene-like climates may be outside the range of evolutionary adaptive capacity.