Abstract
The observed trend in Earth’s energy imbalance (TEEI), a measure of the acceleration of heat uptake by the planet, is a fundamental indicator of perturbations to climate. Satellite observations (2001–2020) reveal a significant positive globally-averaged TEEI of 0.38 ± 0.24 Wm−2decade−1, but the contributing drivers have yet to be understood. Using climate model simulations, we show that it is exceptionally unlikely (<1% probability) that this trend can be explained by internal variability. Instead, TEEI is achieved only upon accounting for the increase in anthropogenic radiative forcing and the associated climate response. TEEI is driven by a large decrease in reflected solar radiation and a small increase in emitted infrared radiation. This is because recent changes in forcing and feedbacks are additive in the solar spectrum, while being nearly offset by each other in the infrared. We conclude that the satellite record provides clear evidence of a human-influenced climate system.
Highlights
The observed trend in Earth’s energy imbalance (TEEI), a measure of the acceleration of heat uptake by the planet, is a fundamental indicator of perturbations to climate
The observed ΔEEI time series yields a significant positive trend of 0.38 ± 0.24 Wm−2decade−1 (Figs. 1a, 2, 3a, 4 and Supplementary Fig. 1a; uncertainty given by 95% confidence interval (CI); hereafter all mentions of uncertainty are given by CI unless otherwise specified)
The model-observation discrepancies and uncertainty are further examined in the Discussion The satellite-observed positive EEI trend over the 2001–2020 period is exceptionally unlikely (
Summary
The observed trend in Earth’s energy imbalance (TEEI), a measure of the acceleration of heat uptake by the planet, is a fundamental indicator of perturbations to climate. TEEI is driven by a large decrease in reflected solar radiation and a small increase in emitted infrared radiation This is because recent changes in forcing and feedbacks are additive in the solar spectrum, while being nearly offset by each other in the infrared. A trend in EEI measures the acceleration of heat uptake by the planet and is an indicator of perturbations to the coupled atmosphere-ocean-land-ice system[4,5,6,7,8]. Satellite observations by Clouds and the Earth’s Radiant Energy System Energy Balance and Filled (CERES EBAF) have provided an uninterrupted two-decade-long time series (January 2001–December 2020) of EEI along with S0, RSW, and OLR, allowing the study of TEEI17. While we know that TEEI is influenced by internal variability in the climate system, external forcings, and climate feedbacks, the extent of the contribution from each has not been previously determined[19,20,21,22,23,24,25,26,27,28,29,30]
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