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2025 Global Temperature - James Hansen and Pushker Kharecha - 15 April 2025
https://www.columbia.edu/~jeh1/mailings/2025/2025GlobalTemperature.15April2025.pdfFigure 1. Global Temperature Anomaly Near Past Three El Nino Events¹
2025 Global Temperature
James Hansen and Pushker Kharecha. 15 April 2025
Global temperature in February and March 2025 fell below the record highs for those months in 2024 (Fig. 1) and such relative decline is likely in most of the next few months. However, the decline has been modest and the 2024 vs 2025 ranks of several months later in the year might be reversed.
Expectation of continuing global temperature change is aided by understanding of the accelerated global warming that began in about 2015. As noted in our “Acceleration” paper, ² the leap of global temperature in 2023-24, in part, had an earlier origin. Interpretations of the 2023 warming are bookended by Raghuraman et al. ³ and Schmidt. ⁴ Raghuraman et al. conclude that the 2023 warming is explained by the El Nino, while Schmidt concludes that the extreme warming cannot be explained by even the full array of mechanisms in global models. Raghuraman et al. note that the 2023 El Nino rose from a deep La Nina, so, despite the El Nino being modest, the Nino4.4 (equatorial Pacific temperature used to characterize El Nino status) change may be sufficient to explain the extreme 2023-24 warming. Here, based on the Acceleration paper, we show that the El Nino accounts for only about half of the 2023-24 warming, and thus Schmidt is partially right: something else important is occurring.
We first (Fig. 2a) remove the long-term trend of global temperature (0.18°C per decade) by subtracting it from the global temperature record since 1970. (The long-term trend is caused by the net greenhouse gas plus aerosol forcing.) What remains is the blue curve in Fig. 2a, which is global temperature change due to other forcings and natural variability. The main source of natural variability is the tropical El Nino cycle, shown by the temperature anomaly in the tropical Nino3.4 region (red curve). Thus, as a second step, we subtract the El Nino variability from the blue curve, ⁵ obtaining the green curve in Fig. 2b. Fingerprints of climate forcings are apparent in the green curve. Most obvious is the 0.3°C global cooling caused by the Pinatubo volcanic eruption, but even the maxima of solar irradiance (a forcing of only ± 0.12 W/m²) cause detectable warmings consistent with prior analyses.⁶
Figure 2. Detrended global and Nino3.4 temperatures (°C) and difference⁷
…
2025 Global Temperature
James Hansen and Pushker Kharecha. 15 April 2025
Abstract. Global temperature for 2025 should decline little, if at all, from the record 2024 level. Absence of a large temperature decline after the huge El Nino-spurred temperature increase in 2023-24 will provide further confirmation that IPCC’s best estimates for climate sensitivity and aerosol climate forcing were both underestimates. Specifically, 2025 global temperature should remain near or above +1.5C relative to 1880-1920, and, if the tropics remain ENSO-neutral, there is good chance that 2025 may even exceed the 2024 record high global temperature.
Global temperature in February and March 2025 fell below the record highs for those months in 2024 (Fig. 1) and such relative decline is likely in most of the next few months. However, the decline has been modest and the 2024 vs 2025 ranks of several months later in the year might be reversed.
Expectation of continuing global temperature change is aided by understanding of the accelerated global warming that began in about 2015. As noted in our “Acceleration” paper, ² the leap of global temperature in 2023-24, in part, had an earlier origin. Interpretations of the 2023 warming are bookended by Raghuraman et al. ³ and Schmidt. ⁴ Raghuraman et al. conclude that the 2023 warming is explained by the El Nino, while Schmidt concludes that the extreme warming cannot be explained by even the full array of mechanisms in global models. Raghuraman et al. note that the 2023 El Nino rose from a deep La Nina, so, despite the El Nino being modest, the Nino4.4 (equatorial Pacific temperature used to characterize El Nino status) change may be sufficient to explain the extreme 2023-24 warming. Here, based on the Acceleration paper, we show that the El Nino accounts for only about half of the 2023-24 warming, and thus Schmidt is partially right: something else important is occurring.
We first (Fig. 2a) remove the long-term trend of global temperature (0.18°C per decade) by subtracting it from the global temperature record since 1970. (The long-term trend is caused by the net greenhouse gas plus aerosol forcing.) What remains is the blue curve in Fig. 2a, which is global temperature change due to other forcings and natural variability. The main source of natural variability is the tropical El Nino cycle, shown by the temperature anomaly in the tropical Nino3.4 region (red curve). Thus, as a second step, we subtract the El Nino variability from the blue curve, ⁵ obtaining the green curve in Fig. 2b. Fingerprints of climate forcings are apparent in the green curve. Most obvious is the 0.3°C global cooling caused by the Pinatubo volcanic eruption, but even the maxima of solar irradiance (a forcing of only ± 0.12 W/m²) cause detectable warmings consistent with prior analyses.⁶
Figure 2. Detrended global and Nino3.4 temperatures (°C) and difference⁷
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