Alarming ocean temperatures helped make 2023 the hottest year

Last year was Earth’s hottest on record by a significant margin and possibly the world's warmest in the last 100,000 years, the European Union's Copernicus Climate Change Service (C3S) said earlier this week. Now, a new study has found that alarming levels of ocean temperatures intensified 2023's extreme heat.

The study, led by an international team of scientists from China, the United States, New Zealand, Italy, and France, aimed to highlight the concerning trends in global warming, specifically those related to ocean temperatures.

Also read: How the climate crisis hit critical stage in 2023

Oceans cover 70% of the planet and absorb about 90% of the heat generated by global warming, which significantly impacts atmospheric conditions. In 2023, the oceans soaked up around 9 to 15 zettajoules more than in 2022, according to the respective estimates from the US National Oceanic and Atmospheric Administration (NOAA) and the Chinese Institute of Atmospheric Physics (IAP). One zettajoule of energy is roughly equivalent to ten times the electricity generated globally in a year, an AFP report said. 

"Annually the entire globe consumes around half a zettajoule of energy to fuel our economies", the researchers explained in a press statement. "Another way to think about this is 15 zettajoules is enough energy to boil away 2.3 billion Olympic-sized swimming pools."

The study, published in the journal Advances in Atmospheric Sciences, further added that in 2023, sea surface temperature and the energy stored in the upper 2000 metres of the ocean both reached record highs. According to AFP, the amount of energy stored in the oceans is a crucial indicator of global warming because it is less affected by natural differences in climate than sea surface temperature.

The study showed that the massive amounts of energy stored in the ocean helped make 2023, the hottest year on record with severe heatwaves, droughts and wildfires. This is linked to a key factor that the warmer the oceans get, the more heat and moisture enter the atmosphere. This results in increasingly erratic weather. Notably, warmer sea surface temperatures are driven mostly by global warming, which is primarily caused by the burning of fossil fuels.

Rising water temperatures and ocean salinity – which was also at an all-time high – contribute to a process of "stratification", where water separates into layers that no longer mix, AFP’s report explains. This impacts the exchange of heat, oxygen and carbon between the ocean and atmosphere, resulting in loss of oxygen in the ocean.

Currently, scientists are worried about the long-term capacity of the Earth’s oceans to absorb more heat.

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