Ocean temperatures in March reached near-record highs, the European Union’s Copernicus Climate Change Service reported, and current conditions point toward “a likely transition toward El Niño conditions.” By comparison, the warmest March on record was 2024, when an El Niño phase drove global temperatures upward.
The World Meteorological Organization has issued a similar outlook: the ongoing La Niña cooling is expected to ease into neutral conditions before shifting to El Niño later this year. El Niño and La Niña are opposite phases of a tropical Pacific climate cycle that produce short-term global temperature swings; El Niño episodes tend to amplify heat extremes on top of long-term warming.
In the United States, federal data show March was the most abnormally hot month in 132 years of records. The Associated Press cited Shel Winkley of Climate Central, who highlighted “the sheer volume of records” after what the agency called the worst snow year and the hottest winter on record. Climate Central also estimated that on March 20–21 roughly one-third of the U.S. experienced unseasonable heat that would have been virtually impossible without human-caused climate change.
Under the 2015 Paris Agreement, countries aim to limit warming to well below 2°C and pursue efforts to stay near 1.5°C. Copernicus reports that global surface air temperatures have risen about 1.3–1.4°C since the pre-industrial era, leaving less room to absorb additional short-term warming from cycles like El Niño.
Polar indicators reflect the broader warming trend. Arctic sea ice extent in March was 5.7% below the 1991–2020 average—the lowest March extent on record, Copernicus said—continuing a steady year-to-year decline in ice cover.
Oceans absorb the majority of excess heat from human activities and play a central role in climate regulation. Warmer seas expand thermally and accelerate polar ice melt, both contributing to sea level rise. Higher ocean temperatures also intensify storms and increase heavy rainfall, trends that have become more frequent in recent years.
Edited by Kieran Burke