Global monthly-mean ocean temperatures are currently at an all-time high; 27% global ocean saw a marine heatwave as of August 15, 2023
There’s a 50-80 per cent chance that marine heatwaves affecting oceans globally will extend to boreal winter 2023, meaning December 2023 through February 2024, according to an analysis by World Meteorological Organization agency World Climate Research Programme (WCRP).
Climate change has contributed to the intensity and widespread coverage of current marine heatwaves, said the programme looking into record warming trends observed globally in recent months.
Marine heatwaves can develop when ocean temperatures in a specific region are significantly higher than average for an extended period of time. The researchers looked into observed basin-wide warming of the ocean and an increase in marine heatwaves.
Instrumental records show global monthly-mean ocean temperatures are currently at an all-time high, said WCRP, potentially extending even further into the past. About 27 per cent of the global ocean experienced a marine heatwave as of August 15, 2023.
The analysis pointed out three main reasons the oceans are heating — El Nino, north Atlantic Oscillation and oceans absorbing a majority of excess heat caused by human activities induced global warming.
El Nino conditions have recently emerged for the first time in seven years — redistributing the upper ocean heat content from west to east across the Pacific and warming it. This explains the intense warming in the eastern equatorial Pacific and the northeast Pacific.
The negative phase of the north Atlantic Oscillation, a natural pattern of atmospheric variability that can impact surface winds and influence ocean temperatures is behind the heating of the North Atlantic, the analysis further said.
However, to definitively pinpoint the precise mechanisms underlying the current marine heatwaves that are occurring in various regions, more information and study are required, the WCRP said.
About 90 per cent of the excess heat associated with global warming has been absorbed by the ocean, causing the global ocean surface temperature to increase by about 0.9 degrees since pre-industrial times.
Long-term warming causes the intensification and persistence of ocean temperature extremes by amplifying the impact of internal climate variations such as El Nino and the north Atlantic Oscillation.
Therefore, it is very likely that climate change has contributed to the intensity and widespread coverage of current marine heatwaves, the WCRP said.
Continuing widespread warming were predicted for coming months by long-range seasonal forecasts and experimental marine heatwave forecasts.
Regionally, the latter forecasts indicate that marine heatwaves in the tropical Atlantic have a 50-80 per cent chance of persisting into boreal winter 2023, although confidence in these forecasts generally decreases with increasing lead time.
Furthermore, as the current El Nino continues to strengthen, models predict an increased risk of marine heatwave conditions along the United States west coast in boreal spring 2024, as events typically peak in austral summer.
The heatwaves are expected to impact marine ecosystems around the globe, resulting in billions of US dollars in damages to marine ecosystems and to industries such as fisheries or tourism. Ocean heat is also an important fuel source for developing tropical cyclones.
The marine heatwaves could lead to rapidly intensifying cyclones and fluctuations in the monsoon rainfall and extreme warming in the tropical Atlantic could contribute to stronger storms, the WCRP researchers further said.
Extreme ocean warming is expected to increase in frequency, duration, and intensity as a result of ongoing global warming caused by unabated greenhouse gas emissions.
If drastic mitigation and adaptation efforts are not undertaken, each increment of future warming may have serious consequences for biodiversity, the structure, and function of marine ecosystems, the analysis added.
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The researchers looked into observed basin-wide warming of the ocean and an increase in marine heatwaves. Photo: iStock.png)
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