An assessment of the Pliocene as an analogue for our warmer future

The Pliocene has been considered a possible palaeoclimate analogue for over four decades and is often referred to as the “best” analogue for the end-of-century future. Using elements of a newly proposed palaeoclimate analogy framework, we critically assess the Pliocene as an analogue for our warmer future using data from the Pliocene Model Intercomparison Project (PlioMIP) and Shared Socioeconomic Pathway (SSP) scenarios from the Sixth Assessment Report (AR6) of the Intergovernmental Panel on Climate Change (IPCC). Three future intervals are considered: near term (2021–2040), medium term (2041–2060), and long term (2081–2100). The strength of the Pliocene as an analogue is found to be highly dependent on a number of factors, including the climate variable and the spatial and temporal scales of interest. Warming under medium emission scenarios (SSP2-4.5 and SSP3-7.0) by the end of this century is found to be the most analogous to the Pliocene, though there is significant variation both between models and between regions on the level of analogy. While increases in Pliocene surface air temperature are found to be analogous to some future scenarios, changes in precipitation are less analogous between the Pliocene and projected futures, particularly in terms of the spatial patterns of change. Using sensitivity experiments, we show that the regions of greatest difference between the Pliocene and projected future(s) are largely attributable to non-CO2 Pliocene boundary conditions, such as reduced land ice and closed Arctic Ocean gateways.