James Hansen, Pushker Kharecha, Dylan Morgan and Jasen Vest 18 December 2025
Abstract. Global temperature in 2025 declined 0.1°C from its El Nino-spurred maximum in 2024, making 2025 the second warmest year. The 2023-2025 mean is +1.5°C relative to 1880-1920. The 12-month running-mean temperature should decline for the next few months, reaching a minimum about +1.4°C. Later in 2026, we expect the 12-month running-mean temperature to begin to rise, as dynamical models show development of an El Nino. We project a global temperature record of +1.7°C in 2027, which will provide further confirmation of the recent global warming acceleration.
Global temperature of +1.47°C in 2025 relative to 1880-1920 is the 2nd highest in the period of instrumental data, about 0.1°C cooler than the 2024 record high (Fig. 1) in the GISS (Goddard Institute for Space Studies) analysis.[1] (We assume the remainder of this month will be about 0.1°C cooler than the same period in 2024; this uncertainty in the exact December temperature has imperceptible effect on the 2025 temperature in Fig. 1). The 3-year (2023-2025) temperature is +1.5°C relative to 1880-1920. We will provide details on the geographical and temporal temperature change in a communication in early 2026.
Two years ago (29 March 2024) we projected[2] that global warming in the then-ongoing El Nino would rise much more than in prior El Ninos, raising global temperature to at least +1.6°C, and that temperature after the El Nino would fall only to +1.4°C (see Fig. 2). (Expectation of unusual warming was based on realization that a long-term global cooling effect of aerosols had recently shifted to warming, as we will discuss further in an upcoming post.) Consistent with this prior projection, we expect a minimum 12-month running-mean temperature of about +1.4°C to be reached in the first half of 2026, after which global temperature should begin a rise that will continue into 2027, reaching a new record high, as discussed below…
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