Global warming: oceans reach record heat levels

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The fever refuses to subside. After terrestrial temperatures, it is now global ocean temperatures that are shattering all records, with devastating consequences for marine ecosystems. Since March 2023, the oceans have been suffocating under extreme temperatures over a period of 450 days. A phenomenon that exceeds the most pessimistic projections of climatologists.

Thanks to a study by the University of Reading (England), we now know why. It was published on January 28 in the journal Environmental Research Letters, and the results are frankly alarming.

A thermal runaway that is accelerating

Thanks to the analysis of satellite data since 1985, researchers have come to this conclusion: the speed of heat absorption has quadrupled in 40 years. Researchers have established a clear correlation between the increase in ocean temperatures and the intensification of the Earth's radiation budget (the difference between the solar radiation absorbed by the Earth and the infrared radiation it emits into space).

It is the latter that determines the Earth's average temperature and it now displays a surplus that has doubled since 2010. This means that more solar energy is absorbed by our planet than infrared energy is reflected back into space. The oceans, which are thermal reservoirs, now absorb 90% of this excess heat.

To illustrate the acceleration of ocean warming, Christopher Merchant, professor of oceanography at Reading, uses the image of a bathtub. In the 1980s, the warming was comparable to a thin stream of hot water. Today, the flow has increased considerably: the tap is open at full capacity, and the water temperature is rising very quickly.

The oceans, victims of a triple punishment

This accelerated warming results from several converging factors. First, greenhouse gases, mainly from the fossil fuel industry, are the main cause, accounting for 44% of excess heat during El Niño years. Warm phases of a natural climate cycle in the Pacific Ocean, characterized by abnormally high water surface temperatures.

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In an unexpected reversal, air pollution control efforts have had a perverse effect: the reduction of sulfur aerosols, particularly in international shipping and Chinese industry, has reduced the formation of marine clouds, which act as our planet's reflective shields. This change in ocean albedo (the proportion of solar radiation reflected by the ocean surface back into space) was combined with the effects of El Niño, which itself injected an additional 0.1 to 0.2°C into the global system.

Merchant explains: ” It is the oceans that dictate the tempo of global warming “.

The repercussions of this thermal disturbance are already under our control. eyes. April 2024 marked a dramatic tipping point: 77% of the world's coral reefs have suffered massive bleaching, endangering not only a quarter of marine biodiversity, but also the livelihoods of a billion people who depend on these ecosystems.

In tropical areas, superheated water masses fuel weather events of formidable intensity. Remember Hurricane Helene?? It was a perfect example: in the space of 24 hours, this tropical system drew on these thermal reservoirs to transform itself from a Category 1 storm into a Category 4 monster before slamming into the Florida coastline. Two weeks later, Hurricane Milton ravaged everything in its path, in the same place.

Climate models for the 2045 horizon are no brighter: the oceanic thermal accumulation of the next two decades could surpass that of the previous forty years. While these simulations contain uncertainties, they are rarely wrong about major trends. In such a situation, the institutional inertia of policymakers is one of our worst enemies, because it jeopardizes our ability to adapt to changes already underway and to limit irreversible damage. And this is precisely what is happening. “The cascading consequences – fires, droughts, floods – will only get worse. It is urgent to become aware of this, but above all for governments to understand that the upheavals to come are likely to be much faster than they anticipate” Merchant alert

• The oceans are experiencing unprecedented warming, accelerated by the massive absorption of excess heat.
• Several factors, including rising greenhouse gases and decreasing marine clouds, are exacerbating this trend.
• The consequences will be catastrophic: endangered marine ecosystems, more violent hurricanes and destructive climate impacts to come in the next decade.

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