Paleoclimate Implications for Human-Made Climate Change

TL;DR

Paleoclimate data reveal Earth's climate sensitivity and feedbacks, indicating that current warming could lead to rapid ice sheet loss and sea level rise, emphasizing the urgency to reduce fossil fuel emissions.

Contribution

This paper integrates paleoclimate evidence with recent observations to highlight the nonlinear nature of ice sheet disintegration and the inadequacy of current warming limits.

Findings

Earth's warmest interglacials were less than 1°C warmer than Holocene.

Ice sheet mass loss may double every 10 years, risking multi-meter sea level rise.

Current temperature exceeds Holocene average, indicating accelerated climate change.

Abstract

Paleoclimate data help us assess climate sensitivity and potential human-made climate effects. We conclude that Earth in the warmest interglacial periods of the past million years was less than 1{\deg}C warmer than in the Holocene. Polar warmth in these interglacials and in the Pliocene does not imply that a substantial cushion remains between today's climate and dangerous warming, but rather that Earth is poised to experience strong amplifying polar feedbacks in response to moderate global warming. Thus goals to limit human-made warming to 2{\deg}C are not sufficient - they are prescriptions for disaster. Ice sheet disintegration is nonlinear, spurred by amplifying feedbacks. We suggest that ice sheet mass loss, if warming continues unabated, will be characterized better by a doubling time for mass loss rate than by a linear trend. Satellite gravity data, though too brief to be conclusive, are consistent with a doubling time of 10 years or less, implying the possibility of multi-meter sea level rise this century. Observed accelerating ice sheet mass loss supports our conclusion that Earth's temperature now exceeds the mean Holocene value. Rapid reduction of fossil fuel emissions is required for humanity to succeed in preserving a planet resembling the one on which civilization developed.