In 2024, the alternation of El Niño and La Niña phenomena had significant impact on global climate conditions. Strong El Niño conditions prevailed at the beginning of 2024, which turned into neutral conditions by the boreal spring and by the end year developed into La Niña-like conditions.

Here are the key influences on global climate conditions in 2024:

• Global temperatures
  • Global average temperature was a record high for the second year in a row in 2024, despite the El Niño quickly waning. The last time temperature records were broken back-to-back was in 2015 and 2016, which were also associated with a strong El Niño event spanning two years.
  • Monthly global surface temperatures were exceptionally high throughout the year, with each month ranking as either the warmest or second warmest on record.
  • Average lake surface water temperature (LSWT) was the largest in 2024 since records began in 1995, with positive anomalies in 79% out of 1944 lakes studied. In regions such as Canada and Europe, average LSWT anomalies were also the largest since 1995.
  • Record high global lower troposphere temperature (LTT) values, which persisted from the second half of 2023 until the boreal summer of 2024, make 2024 the warmest year for global LTT in all nine datasets considered.
  • Anomalies of surface and lower-tropospheric temperatures, near-surface specific humidity, and total column water vapor (TCWV) were record high in 2024, consistent with the presence of El Niño for part of the year.
• Oceans
  • Sea surface temperatures (SST) broke records in 2023 and persisted into 2024, with daily global average SSTs in 2024 significantly above normal throughout the year.
  • Temperature anomalies at sea level, they showed a typical El Niño pattern during the boreal winter (December 2023–February 2024), which weakened in the spring and transitioned into a weak La Niña pattern in the eastern and central equatorial Pacific in the summer and autumn.
  • Maritime heat waves were more extensive, longer-lasting and more severe in 2024 than in previous years.
  • Ocean heat content (OHC) from 0 to 2000 dbar reached record high levels in 2024, with a strong El Niño signature during the boreal winter of 2023/24. The transition from El Niño to a neutral phase led to a decrease in OHC across the entire equatorial Pacific.
  • Global Mean Sea Level (GMSL) increased by 4.6 (±1.4) mm and reached record high levels in 2024, with its anomalies peaking in March as strong El Niño conditions were ending. In the second half of the year, GMSL anomalies decreased due to the transition to neutral ENSO conditions and subsequently to La Niña-like conditions.
  • Surface currents in the equatorial Pacific, they were significantly anomalous westerly in 2024, reflecting a shift from strong El Niño to weak La Niña conditions.
  • Ocean carbon sequestration was estimated to be about 2.7 Pg C per year in 2024, below the 2014–2023 average, due to reduced outflow and lower CO₂ emissions in the eastern equatorial Pacific due to El Niño in the early months of the year.
  • Global ocean phytoplankton showed chlorophyll-a anomalies low in the central and eastern equatorial Pacific but high just beyond this band, consistent with initially strong but waning El Niño conditions.
• Atmospheric composition and humidity
  • Concentrations of major greenhouse gases – carbon dioxide, methane and nitrous oxide – continued to rise to record high levels. The annual increase in CO₂ of 3.4 ppm from 2023 to 2024 matched the increase in 2015/16, the highest increase since the 1960s. This increase is likely driven by record high global temperatures and large-scale carbon emissions from fires, influenced by ENSO.
  • Total Column Water Vapor (TCWV) 2024 was the wettest on record for all six datasets and for all three domains (global, ocean, and land), surpassing 2023, which had already set records in some datasets.
  • Upper Tropospheric Humidity (UTH) was slightly below normal in 2024, especially in the first half of the year, as expected during an El Niño. The anomalies decreased substantially in late 2024 as El Niño dissipated.
  • Tropospheric ozone reached the highest tropospheric ozone (TOB) load in 2024 since OMI/MLS records began in 2004. In the tropics, lower stratospheric ozone values were very low due to a strong El Niño and the easterly phase of the QBO.
  • Stratospheric water vapor (WV) was still strongly influenced by the January 2022 eruption of Hunga Volcano. However, the WV anomalies in the tropical lower stratosphere in 2024 followed a typical pattern influenced by tropical tropopause temperature anomalies that are correlated with ENSO and QBO.
• Rainfall and drought
  • Global precipitation: 2024 was the third wettest year globally since 1983, with precipitation over the oceans much higher than normal, likely due to above-average sea surface temperatures and the El Niño phenomenon.
  • Regional precipitation: Excess precipitation was observed in most of the tropics, Asia and the northwest Pacific, as well as in the northern and southern subtropical Atlantic. Precipitation deficit was recorded in southern Africa, the southeastern Indian Ocean, the subtropical Pacific, South America and the North Atlantic.
  • The impact of ENSO on regional precipitation patterns: El Niño conditions early in the year led to below-normal rainfall in southern Africa and above-normal rainfall in East Africa, East Asia, southwestern North America, and the northern Gulf of Mexico. These conditions dissipated in the second half of 2024.
  • Drought: 2024 was again a dry year in terms of river flows and runoff, continuing a four-year trend of below-normal global runoff and a six-year trend of below-normal global river flow.
  • Soil moisture anomalies were more extensive and intense in many areas, including widespread dry anomalies in the Amazon, central and southern Africa, and Mexico, which persisted from 2023. On the other hand, particularly extensive and pronounced positive anomalies were recorded in East Africa, the Arabian Sea, central India, northeastern Australia, and adjacent areas of the western Pacific.
• Ice and water bodies
  • Ice cover of lakes: Lakes in the Northern Hemisphere tended to freeze later, melt earlier, and have shorter ice cover durations, consistent with long-term trends. The Laurentian Great Lakes had 31.8 % less maximum ice cover during the winter of 2023/24 compared to the 1991–2020 average.
  • Lake levels and water reserves: Globally, there was a slight increase in lake water levels and reserves in 2024, with 57.8 % lakes experiencing an increase and 42.2 % decreasing compared to the 1993–2020 base period.
  • Greenland Ice Sheet: Mass losses were dampened in the summer of 2024 by anomalous polar air inflow from the north and snowfall. The extremely positive Arctic Oscillation Index (AOI) contributed to this by keeping cold air in the Arctic, shielding Greenland from warm southern air.
• Vegetation and land surface
  • Vegetation optical density (VOD): Negative anomalies prevailed in the Southern Hemisphere, especially in the first quarter, during a strong El Niño. Extensive positive anomalies were observed in Australia and parts of East Africa.

These changes are evidence of a complex link between the ENSO cycle and global climate conditions, with El Niño having a dominant influence at the beginning of the year and its transition to La Niña-like conditions influencing further developments in the second half of 2024. JRi

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