Hurricanes, heatwaves and rising seas: The impacts of record ocean heat
Record ocean temperatures suggest the seas are warming faster than expected, and the impacts will be felt from polar ice shelves to coastal cities across the globe.
The world's oceans are like a planet-sized battery: they absorb huge amounts of heat, which is then released slowly. So far, our oceans have soaked up over 90% of the heat trapped in the Earth's atmosphere by rising greenhouse gas emissions. But recently, their rate of warming has been dramatic.
Every day since late March 2023, global ocean surface temperatures have set new records for the hottest temperature ever recorded on that date. On 47 of those days, temperatures have also surpassed previous highs by the largest margin seen in the satellite era, according to data from the European Union's Copernicus Climate Change Service. (Read the analysis of the data in this article by the BBC News Climate and Science team.)
In February 2024, the world had breached 1.5C warming of surface air temperatures for a full year. But in some regions last year, ocean temperatures were similar to those expected if overall global warming of surface air temperatures reached 3C above pre-industrial levels – suggesting quicker ocean heating than expected.
This rapid heating raises a puzzle for scientists: why is recent ocean warming even greater than models suggest?
What is clear, however, is that ocean warming is already having damaging effects on people and ecosystems alike. In summer 2023, buoys off the coast of Florida recorded temperatures that were warmer than a hot tub. Coral reefs are currently undergoing their fourth planet-wide bleaching event, set to be the most extensive yet.
Other impacts are less talked about: from de-oxygenation of the deep seas, to more intense rain in the skies above. All indicate that record ocean temperatures are destabilising the planet.
What's causing record ocean warming?
Two factors are primarily responsible for the past year's record ocean heat, says Michael McPhaden, an oceanographer at the National Oceanic and Atmospheric Administration (Noaa) in the US. The first is the atmosphere's ever-rising greenhouse gas concentrations.
The second was 2023's major El Niño event, in which warmer-than-average surface waters in the tropical Pacific Ocean led to increased evaporation – and a vast transfer of heat to the atmosphere.
Even accounting for these factors, their inputs still don't quite add up to the amount of ocean warming some areas are currently experiencing, says McPhaden. Parts of the northern Atlantic, for instance, are currently "extraordinarily" warm, for reasons still not well understood.
Researchers are just beginning to investigate other factors. In one early study that has yet to be peer reviewed, Noaa oceanographer Boyin Huang attempts to explain the shortfall by pointing to another long-term (50-70 year) cycle of ocean heating and cooling in the higher latitudes.
While the causes of today's record ocean heat are still to be understood, its impacts are already making themselves felt around the world.
bbc.com
