From mid-March The world's oceans are warmer than at any time since at least 1982, raising concerns among some climate experts about accelerated warming. Why is this important: Warming oceans have a huge impact on land, as they can contribute to more frequent and severe extreme weather and climate events, from floods to heat waves. In addition, the temperature jump could be a sign that warming is accelerating in ways that climate models have failed to predict. Zoom in: While the record for global average sea surface temperatures is remarkable and far-reaching, that’s no reason to lose sight of the bigger picture, climatologists told Axios. The rise in sea surface temperatures, captured by a network of ships, buoys and satellites, is likely driven by a combination of an emerging El Niño in the tropical Pacific and another trend that has scientists far more concerned. When a La Niña event gives way to an El Niño, as is happening now, a large amount of ocean heat that was hidden beneath the ocean’s surface is pulled up, according to Michael Mann, a climate scientist at the University of Pennsylvania. The result, Mann told Axios via email, is a “significant increase” in tropical Pacific and global ocean temperatures during the transition. “La Niña buries some ocean heat beneath the surface, and El Niño brings that heat back to the surface,” Mann said. Context: El Niño events are defined by above-average ocean temperatures in the equatorial tropical Pacific, along with myriad changes in weather patterns. Such ocean-atmosphere cycles occur naturally and help temporarily accelerate or, in the case of La Niña, slow the rate of climate change. This is one reason why the long-term record of surface temperatures resembles a staircase rather than a straight line. Threat level: The steady and record-breaking accumulation of ocean heat in the water column, not just at the surface, is actually more concerning to climate scientists than the recent rise in sea surface temperatures. Researchers like Mann and Kevin Trenberth of the National Center for Atmospheric Research (NCAR) told Axios that this is a clearer sign of human-caused global warming than the ongoing record sea surface temperatures. The oceans absorb more than 90 % of additional heat from the Earth’s atmosphere due to greenhouse gas emissions from fossil fuel burning and other causes. The ocean’s heat content, measured in the water column from the surface to a depth of 2,000 meters (6,561 feet), reached a record high in 2022. A recent study found that this is changing the vital ocean currents that distribute heat and nutrients around the world. (Andrew Freedman, author of Axios Generate)