Updated attribution of GSAT changes and implications

The observed increase of global air surface temperature (GSAT) has long been attributed to human activities. However, updating estimates of human-induced changes, and changes induced by specific subsets of forcings (e.g., green-house gases) remains of high interest to better understand recent changes and also produce refined projections.

Here, we use the newest climate model ensemble (CMIP6), improved observations, and a new statistical method to narrow uncertainty on the response to historical forcings. In addition, we focus on estimating the total warming since the pre-industrial (using 1850-1900 as a reference baseline), while most previous studies considered shorter periods.

Results suggest that most of the observed warming since the pre-industrial (+1.22°C +/-0.15°C in 2020) is human-induced (+1.15°C +/-0.15°C) and that a substantial fraction of GHG-induced warming (+1.54°C +/-0.33°C) has been offset by other anthropogenic factors (-0.39°C +/-0.28°C). We also quantify the contribution of specific forcings to the 2010-2019 warming rate, suggesting that the current rate of human-induced warming is +0.22°C/decade (+/-0.05°C/decade). We then derive implications of these findings in terms of future climate change, i.e., the response to a range of scenarios. Our results suggest that historical observations and historical climate change are already very informative about future changes and the property of the Earth System in general.