A recent episode of rapid ocean warming is causing growing concern, and scientists are unsure of the consequences of this phenomenon.
This month, the surface temperature of the oceans reached a new record. It has never grown so rapidly. Scientists don’t fully understand why this happened. But they fear that, combined with other weather events, the global temperature could reach a worrying level by the end of next year. Experts believe that a strong El Niño weather event, a weather system that warms the ocean, will also set in over the next few months.
An important new study, released last week without much fanfare, highlights a worrying development. Over the past 15 years, the Earth has accumulated almost as much heat as in the previous 45 years, with most of the additional energy being absorbed by the oceans. This has real consequences – not only did global ocean temperature hit a new record high in April this year, but in some regions the deviation from the long-term average was huge. In March, sea surface temperatures off the east coast of North America were up to 13.8°C warmer than the 1981-2011 average.
“It is not yet well established why such a rapid and significant change is occurring,” said Karina Von Schuckmann, the lead author of the new study and an oceanographer with the Mercator Ocean International research group. “We’ve doubled the heat in the climate system in the last 15 years. I don’t want to say whether it’s climate change or natural variability, or a mix of the two, we don’t know yet. But we’re seeing this change.”
One factor that could influence the amount of heat absorbed by the oceans is, curiously, a reduction in pollution from shipping. In 2020, the International Maritime Organization introduced regulations to reduce the sulfur content of fuel burned by ships. This had a quick impact, reducing the amount of aerosol particles released into the atmosphere. But the aerosols that dirty the air also help reflect heat back into space – removing them may have caused more heat to enter the waters.
Another major factor worrying scientists is the weather phenomenon known as the El Niño Southern Oscillation. For the past three years, this natural event has been in a colder phase called La Niña, and has helped contain rising global temperatures.
However, researchers now believe that a strong El Niño is forming, which will have significant implications for the world. “The Australian Bureau’s model strongly leans towards a strong El Niño. And it’s moving in that direction, and all climate models are moving towards a stronger event,” said Hugh McDowell of the Australian Bureau of Meteorology. McDowell said predictions at this point in the year are less reliable. Other researchers are more optimistic.
A coastal El Niño has already developed off the coasts of Peru and Ecuador, and experts believe a fully formed event will follow with implications for global temperatures. “If a new El Niño is added to this, we will probably have an additional global warming of 0.2 to 0.25°C,” said Dr Josef Ludescher of the Institute for Climate Research in Potsdam. “The impact on temperature dissipates a few months after El Niño peaks, which is why 2024 is likely to be the hottest year on record.”
“And we could approach 1.5°C and maybe even exceed it temporarily.” But there are more fundamental concerns: as the heat in the ocean increases, the waters may be less able to store excess energy. And there are concerns that the heat contained in the oceans does not stay there.
Some research has shown that the world warms in leaps, with little change over a period of years, then sudden upward leaps, like stair steps, closely linked to the development of El Niño. According to Karina Von Schuckmann, there is hope in this scenario. Temperatures could drop again after the end of the El Niño. “We still have a window of action to reduce the consequences, and we should use it,” she told BBC News.