Indicators of Global Climate Change 2025: annual update of key indicators of the state of the climate system and human influence

Abstract. In a rapidly changing climate, evidence-based decision-making benefits from up-to-date and timely information. We track twelve key sets of indicators of the state of the climate system, closely following Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment report (AR6) methods, to produce our fourth annual publication. One of the indicators, the Earth's energy imbalance (EEI) provides a crucial integrative measure of the pace of climate change – this has more than doubled since the 1976–1995 period. A newly updated indicator of temperature extremes, the number of days experiencing marine heatwaves, has more than tripled between 1991 and 2025. For the 2016–2025 decade average, observed warming relative to 1850–1900 was 1.26 [1.13 to 1.36] °C, of which 1.24 [1.0 to 1.5] °C was human-induced. Human-induced warming reached 1.37 °C relative to 1850-1900 in the year 2025, increasing at a rate of 0.27 [0.2–0.4] °C per decade over 2016–2025. This high rate of warming, which matches the all-time high seen last year in the instrumental record, was caused by a combination of greenhouse gas emissions being at an all-time high of 54.6 ± 5.5 GtCO2e per year over the last decade (2015–2024), as well as reductions in the strength of aerosol cooling. Despite this, there is evidence that CO2 emission growth is slowing. The continuation of these annual updates could track decreases or increases in the rate of human influence and climatic changes presented here, reflecting the outcomes of societal choices during the critical 2020s decade. In total, we employ analysis from over 40 global datasets (https://doi.org/10.5281/ZENODO.7883757 Smith et al., 2026a) These data are threatened by geopolitical and public funding decisions that are cutting support for key satellite and in-situ observing programs critical for the monitoring of the atmosphere, ocean, cryosphere and land surface, including long-term data preservation and provision that is key to understanding our changing climate for today and for future generations. Overall, the Global Climate Observing System (GCOS) framework, which supports much of our international capability, is under threat. Our ability to monitor effectively many of the indicators presented herein is not guaranteed without concerted international action to ensure the continuity of observation programs and coordination mechanisms, including the GCOS program, that enable their effective integration and use.