Indicators of Global Climate Change 2023: annual update of key indicators of the state of the climate system and human influence

AR6 WGI Chap. 2 assessed the 2001–2020 globally averaged surface temperature change above an 1850–1900 baseline to be 0.99 [0.84 to 1.10] °C and 1.09 [0.95 to 1.20] °C for 2011–2020 (Gulev et al., 2021). Updated estimates to 2022 of 1.15 [1.00–1.25] °C were given in AR6 SYR (Lee et al., 2023), matching the estimate in Forster et al. (2023).

There are choices around the methods used to aggregate surface temperatures into a global average, how to correct for systematic errors in measurements, methods of infilling missing data, and whether surface measurements or atmospheric temperatures just above the surface are used. These choices, and others, affect temperature change estimates and contribute to uncertainty (IPCC AR6 WGI Chap. 2, Cross Chap. Box 2.3, Gulev et al., 2021). The methods chosen here closely follow AR6 WGI and are presented in Sect. S6. Confidence intervals are taken from AR6 as only one of the employed datasets regularly updates ensembles (see Sect. S6).

\hack{\newpage}Based on the updates available as of March 2024, the change in global surface temperature from 1850–1900 to 2014–2023 is presented in Fig. 5. These data, using the same underlying datasets and methodology as AR6, give 1.19 [1.06–1.30] °C, an increase of 0.10 °C within 3 years from the 2011–2020 value reported in AR6 WGI (Table 5) and 0.09 °C from the 2011–2020 value in the most recent dataset versions. The change from 1850–1900 to 2004–2023 was 1.05 [0.90–1.16] °C, 0.07 °C higher than the value reported in AR6 WGI from 3 years earlier. These changes, although amplified somewhat by the exceptionally warm 2023, are broadly consistent with typical warming rates over the last few decades, which were assessed in AR6 as 0.76 °C over the 1980–2020 period (using ordinary-least-squares linear trends) or 0.019 °C per year (Gulev et al., 2021). They are also broadly consistent with projected warming rates from 2001–2020 to 2021–2040 reported in AR6, which are on the order of 0.025 °C per year under most scenarios (Lee et al., 2021). See Sect. 7.4 for further discussion of trends.

The global surface temperature in 2023 was 1.43 [1.32 to 1.53] °C above the 1850–1900 average in the multi-dataset mean used here. This is similar to the combined estimate from six datasets quoted in the 2023 WMO State of the Global Climate report, 1.45 [1.33 to 1.57] °C (WMO, 2024). As seen in Fig. 5 and discussed in Sect. 7.3, this is considerably above the human-induced warming estimate, indicating a significant role of internal variability.