The overshoot integral can inform climate science and policy beyond 1.5 °C of warming
- 1University of Exeter
- 2International Institute for Applied Systems Analysis
- 3Department of Earth System Science, Tsinghua University
Abstract
The carbon budget framework has served as the dominant organising principle for climate science and policy, linking cumulative emissions to peak warming and providing a tractable scalar constraint for international negotiations. With 1.5 °C exceedance now imminent and virtually all mitigation scenarios involving substantial temperature overshoot before net-negative emissions could return temperatures to target, the budget framework’s utility for evaluating and minimising risk generated by warming risks becoming diminished. We propose a complementary organising principle: the overshoot integral, defined as the time-integrated temperature exceedance above a policy-relevant threshold, with units of °C·years. Analogous to degree-heating weeks in coral bleaching prediction and positive degree-days in glaciology, the overshoot integral captures both the magnitude and duration of exceedance in a single scalar quantity. Applying this metric to future climate pathways, we show that pathways with similar peak temperatures can differ by more than two orders of magnitude in their cumulative degree-year burden. Applied to CMIP7 ScenarioMIP/FaIR (Finite Amplitude Impulse Response simple climate model) trajectories, calculating overshoot integrals reveal substantial differences in cumulative thermal exposure across pathways. For Earth-system impacts whose response dynamics integrate forcing over time, spanning marine habitat, permafrost carbon and mountain glaciers, we show that cumulative thermal exposure captured by the overshoot integral contains impact-relevant information not captured by peak warming alone. A simple risk formulation combining peak and cumulative exposure improves out-of-sample prediction across all three systems. That the overshoot integral is best understood not as a reversible account that can be debited and credited, but as a cumulative dose should inform climate policy and science in the increasingly warmer future.
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BibTeX
@article{dyke2026overshoot,
title = {{The overshoot integral can inform climate science and policy beyond 1.5 °C of warming}},
author = {James G Dyke and Jesse F Abrams and Hans Joachim Schellnhuber},
journal = {Environmental Research Letters},
year = {2026},
month = oct,
doi = {10.1088/1748-9326/aeb55a},
url = {https://iopscience.iop.org/article/10.1088/1748-9326/aeb55a},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - The overshoot integral can inform climate science and policy beyond 1.5 °C of warming
AU - James G Dyke
AU - Jesse F Abrams
AU - Hans Joachim Schellnhuber
PY - 2026
DA - 2026/10/27
JO - Environmental Research Letters
DO - 10.1088/1748-9326/aeb55a
UR - https://iopscience.iop.org/article/10.1088/1748-9326/aeb55a
AB - The carbon budget framework has served as the dominant organising principle for climate science and policy, linking cumulative emissions to peak warming and providing a tractable scalar constraint for international negotiations. With 1.5 °C exceedance now imminent and virtually all mitigation scenarios involving substantial temperature overshoot before net-negative emissions could return temperatures to target, the budget framework’s utility for evaluating and minimising risk generated by warming risks becoming diminished. We propose a complementary organising principle: the overshoot integral, defined as the time-integrated temperature exceedance above a policy-relevant threshold, with units of °C·years. Analogous to degree-heating weeks in coral bleaching prediction and positive degree-days in glaciology, the overshoot integral captures both the magnitude and duration of exceedance in a single scalar quantity. Applying this metric to future climate pathways, we show that pathways with similar peak temperatures can differ by more than two orders of magnitude in their cumulative degree-year burden. Applied to CMIP7 ScenarioMIP/FaIR (Finite Amplitude Impulse Response simple climate model) trajectories, calculating overshoot integrals reveal substantial differences in cumulative thermal exposure across pathways. For Earth-system impacts whose response dynamics integrate forcing over time, spanning marine habitat, permafrost carbon and mountain glaciers, we show that cumulative thermal exposure captured by the overshoot integral contains impact-relevant information not captured by peak warming alone. A simple risk formulation combining peak and cumulative exposure improves out-of-sample prediction across all three systems. That the overshoot integral is best understood not as a reversible account that can be debited and credited, but as a cumulative dose should inform climate policy and science in the increasingly warmer future.
SN - 1748-9326
ER -