Oceans are warming – what does it mean for the world?
The world’s oceans are hotter than ever before, as climate change combines with a powerful El Niño.
Why do sea surface temperatures matter?
The oceans cover more than 70% of the Earth’s surface. They absorb the majority of solar heat and retain it longer than the land or the atmosphere.
Sea surface temperature – also known as SST – is a significant component of the Earth’s climate system as it impacts the exchanges of energy and gases between the ocean and the atmosphere. SST is an essential tool in weather forecasting and atmospheric model simulations, as well as ecosystem and marine life monitoring and management, and even tourism. In particular, SST helps to identify the El Niño and La Niña cycles, which impact global weather patterns, ocean circulation, and marine ecosystems. We are currently entering a new El Niño, which means that the sea temperatures in the Pacific near the equator are warmer than average.
SST is measured with the use of remote sensing instruments like satellites, and direct measurement instruments, like buoys and ships.
What’s unusual about sea surface temperatures this year?
The daily global average SST reached its highest temperature on record in August this year. The Copernicus Climate Change Service, which has been monitoring SST since 1979, confirmed that the temperature reached 21.1°C on 22 August, compared to the previous record of 21.09°C in March 2024. The timing of this record is unusual too, as typically global ocean temperatures reach their highest peak in March and April.
As El Niño – set to be the hottest in at least a century – continues to develop, oceans are expected to continue to warm.
How do ocean temperatures affect the UK and the world?
From damaged fisheries to extreme weather events, the rise in ocean temperatures has consequences that spread across the whole world.
A warmer ocean contributes to sea level rise since warm water takes up more space. This increases risk of flooding, endangering coastal communities.
Warmer water transfers more heat and moisture to the atmosphere, intensifying rainfall and storms. Warmer oceans can also amplify heatwaves by reducing the cooling effect of sea breezes.
Warmer oceans increase the likelihood of marine heatwaves, which can lead to coral bleaching and reef loss, disruption of fish populations, and harmful algae blooms, among other effects.
A warmer ocean becomes less efficient at absorbing carbon dioxide (CO2). Oceans store most of the CO2 that gets released into the atmosphere from the burning of fossil fuels, which means that a reduced capacity to absorb CO2 can lead to accelerated global warming.
Is there a trend of seas getting warmer across recent years?
This new SST record reflects the continued long-term warming of the global ocean. Due to human-induced climate change, warm ocean events are not only becoming more frequent, but they are also more severe and last longer.
According to the National Oceanography Centre, the number of marine heatwaves has doubled since 1982. At the same time, cold marine conditions have become increasingly rare.