The Tropics

This is the authors' abstract. We don't add key points for this paper.

In 2024, the Oceanic Niño Index (ONI; Fig. 4.1) transitioned from El Niño during the early part of the year to a neutral phase of the El Niño-Southern Oscillation (ENSO) during the Northern Hemisphere spring of 2024. El Niño developed in boreal spring 2023, strengthened steadily through the summer and autumn, and then peaked in November 2023-January 2024. In April-June (AMJ) 2024, El Niño transitioned to ENSO-neutral, where it continued through October-December 2024. For the global tropics (defined here as 20°S-20°N), the NOAA Merged Land Ocean Global Surface Temperature Analysis (NOAA GlobalTemp; Vose et al. 2021) indicates that the combined average land and ocean surface temperature was 1.20°C above the 1991-2020 average, making 2024 the warmest year for the tropics in the 175-year data record. The seven warmest years in the tropics since 1850 have all occurred from 2015 onward. Data from the Global Precipitation Climatology Project indicate a mean annual total precipitation value of 1377 mm across the tropics over land. This is 50 mm below the 1991-2020 average and was the eighth lowest for the 1979-2024 period of record.