Indicators of Global Climate Change 2023: annual update of key indicators of the state of the climate system and human influence
Authors: Forster Piers M. , Smith Chris , Walsh Tristram , Lamb William F. , Lamboll Robin , Hall Bradley , Hauser Mathias , Ribes Aurélien , Rosen Debbie , Gillett Nathan P. , Palmer Matthew D. , Rogelj Joeri , von Schuckmann Karina , Trewin Blair , Allen Myles , Andrew Robbie , Betts Richard A. , Borger Alex , Boyer Tim , Broersma Jiddu A. , Buontempo Carlo , Burgess Samantha , Cagnazzo Chiara , Cheng Lijing , Friedlingstein Pierre , Gettelman Andrew , Gütschow Johannes , Ishii Masayoshi , Jenkins Stuart , Lan Xin , Morice Colin , Mühle Jens , Kadow Christopher , Kennedy John , Killick Rachel E. , Krummel Paul B. , Minx Jan C. , Myhre Gunnar , Naik Vaishali , Peters Glen P. , Pirani Anna , Pongratz Julia , Schleussner Carl-Friedrich , Seneviratne Sonia I. , Szopa Sophie , Thorne Peter , Kovilakam Mahesh V. M. , Majamäki Elisa , Jalkanen Jukka-Pekka , van Marle Margreet , Hoesly Rachel M. , Rohde Robert , Schumacher Dominik , van der Werf Guido , Vose Russell , Zickfeld Kirsten , Zhang Xuebin , Masson-Delmotte Valérie , Zhai Panmao 
Published: June 2024

Abstract. Intergovernmental Panel on Climate Change (IPCC) assessments are the trusted source of scientific evidence for climate negotiations taking place under the United Nations Framework Convention on Climate Change (UNFCCC). Evidence-based decision-making needs to be informed by up-to-date and timely information on key indicators of the state of the climate system and of the human influence on the global climate system. However, successive IPCC reports are published at intervals of 5–10 years, creating potential for an information gap between report cycles. We follow methods as close as possible to those used in the IPCC Sixth Assessment Report (AR6) Working Group One (WGI) report. We compile monitoring datasets to produce estimates for key climate indicators related to forcing of the climate system: emissions of greenhouse gases and short-lived climate forcers, greenhouse gas concentrations, radiative forcing, the Earth's energy imbalance, surface temperature changes, warming attributed to human activities, the remaining carbon budget, and estimates of global temperature extremes. The purpose of this effort, grounded in an open-data, open-science approach, is to make annually updated reliable global climate indicators available in the public domain (https://doi.org/10.5281/zenodo.11388387, Smith et al., 2024a). As they are traceable to IPCC report methods, they can be trusted by all parties involved in UNFCCC negotiations and help convey wider understanding of the latest knowledge of the climate system and its direction of travel. The indicators show that, for the 2014–2023 decade average, observed warming was 1.19 [1.06 to 1.30] °C, of which 1.19 [1.0 to 1.4] °C was human-induced. For the single-year average, human-induced warming reached 1.31 [1.1 to 1.7] °C in 2023 relative to 1850–1900. The best estimate is below the 2023-observed warming record of 1.43 [1.32 to 1.53] °C, indicating a substantial contribution of internal variability in the 2023 record. Human-induced warming has been increasing at a rate that is unprecedented in the instrumental record, reaching 0.26 [0.2–0.4] °C per decade over 2014–2023. This high rate of warming is caused by a combination of net greenhouse gas emissions being at a persistent high of 53±5.4 Gt CO2e yr−1 over the last decade, as well as reductions in the strength of aerosol cooling. Despite this, there is evidence that the rate of increase in CO2 emissions over the last decade has slowed compared to the 2000s, and depending on societal choices, a continued series of these annual updates over the critical 2020s decade could track a change of direction for some of the indicators presented here.