Arctic amplification: can the past constrain the future?

Arctic amplification, the observation that surface air temperature changes in the Arctic exceed those of the Northern Hemisphere as a whole, is a pervasive feature of climate models, and has recently emerged in observational data relative to the warming trend of the past century. The magnitude of Arctic amplification is an important, but poorly constrained variable necessary to estimate global average temperature change over the next century. Here we evaluate the mechanisms responsible for Arctic amplification on Quaternary timescales, and review evidence from four intervals in the past 3 Ma for which sufficient paleoclimate data and model simulations are available to estimate the magnitude of Arctic amplification under climate states both warmer and colder than present. Despite differences in forcings and feedbacks for these reconstructions compared to today, the Arctic temperature change consistently exceeds the Northern Hemisphere average by a factor of 3–4, suggesting that Arctic warming will continue to greatly exceed the global average over the coming century, with concomitant reductions in terrestrial ice masses and, consequently, an increasing rate of sea level rise.