Global ocean surface temperature hit a new record high this month, and scientists do not fully understand why.
From April 1 the temperature hit 21.1C for six successive days, the highest since records began, topping the previous figure of 21.0C set in 2016.
Warmer seas cause a number of concerns for scientists, not least their effect on overall global temperature. Combined with a strong El Niño forecast over the next few months, the phenomenon could push the world closer to the 1.5C global temperature increase international governments have pledged not to exceed.
The world’s oceans help regulate climate change by absorbing both carbon and heat. However, seas cannot continue to absorb heat indefinitely without consequence. Around the world, marine life is showing signs of heat stress, from headline-making coral reef bleaching and melting sea ice to the loss of sea kelp forests – another critical player in carbon removal.
‘It’s not yet well established why such a rapid change [occurred],’ said Karina Von Schuckmann, oceanographer at the research group Mercator Ocean International that produced the latest data.
Speaking to the BBC, she added: ‘We have doubled the heat in the climate system in the last 15 years. I don’t want to say this is climate change, or natural variability or a mixture of both, we don’t know yet – but we do see this change.’
Ironically, a reduction in shipping pollution could be contributing to the warming.
A 2020 treaty by the International Maritime Organisation reduced the amount of sulphur in fuel used by ships. This has resulted in a rapid reduction in the volume of pollutant particles in the atmosphere, which previously helped reflect heat back into space. With a lower concentration of aerosol particles, more heat is reaching the Earth’s surface, but the team has not been able to confirm the link.
However, meteorologists are predicting a strong El Niño will contribute to further ocean warming.
‘Sea-surface temperatures have seen a sudden rise in March with global datasets showing figures well above normal levels continuing into April,’ said Dr Simon Good, a marine analyst at the Met Office.
‘Later this year we expect an El Niño to occur, which is part of a cycle of natural variability within the climate system involving both the ocean and the atmosphere. It is said to have occurred if sea surface temperatures in the tropical eastern Pacific rise 0.5C above the long-term average.
‘For the last three years the tropical Pacific has been in the opposing phase with a La Niña bringing cooler conditions.
‘With the strong potential for an El Niño event in the mix we can expect sea surface temperatures to temporarily rise further, with a consequent knock-on effect for global temperature as a whole.’
Warmer oceans also lead to more intense storms, posing a further risk to humans on land.
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