Recent studies indicate that global warming has not only increased the temperatures of the seas but also accelerated the speed at which this was happening. In 2019, the highest temperature, since data became available, was recorded. Specifically in the area between the surface and the first 2,000 metres deep.
According to a study published in the journal Advances and Atmospheric Sciences, the temperature of the ocean in 2019 is approximately 0.075 °C above the average temperature recorded between 1981- 2010. In order to explain this figure, the authors use a chilling analogy claiming that: in the last 25 years the oceans have received a quantity of heat equivalent to 3.6 billion explosions from atomic bombs such as Hiroshima.
The work that was carried out by scientists, from eleven institutions around the world, used a new analysis system to examine two independent sets of ocean water temperature data. This way they were able to examine changes in ocean temperatures since the 1950s. They discovered that in the last three decades (1987-2019) global warming has been 450% greater than in the previous three decades (1955-1986).
Why is ocean warming relevant (and worrying)?
It is estimated that, since 1970, the oceans have absorbed more than 90% of the heat produced by the emission of greenhouse gases, while less than 4% of the heat would have been absorbed by land and the atmosphere. Therefore, if we only take into account the increase in atmospheric temperatures we will only see the tip of the iceberg. "If we want to understand global warming, we have to study ocean warming," stresses John Abraham, professor at St. Thomas University in the United States and co-author of the paper.
We don't live in the sea, but what happens there affects us because the relationship between the ocean and the atmosphere goes hand in hand. The warming of the oceans causes changes in atmospheric circulation that can lead to droughts, floods and changes in the rainfall regime at any point on the planet. Not to mention sea-level rise, which threatens to wipe out some of the world's most densely populated cities.
Marine life is also affected by warming waters. The authors cite the example of what has been called "the blob", a huge body of warm water detected in the Pacific in 2013. "The blob caused very serious damage to marine life and affected phytoplankton, zooplankton, fish and whales," recalls Kevin Trenberth, a researcher at the U.S. National Center for Atmospheric Research and co-author of the study. "These manifestations of global warming have serious consequences.”
The team of scientists is now investigating the implications of this ocean warming on issues such as water buoyancy, a characteristic that in turn determines the distribution of nutrients and heat in the oceans.
In September 2019, the Intergovernmental Panel on Climate Change (IPCC) published its special report on oceans, in which it recalled that very profound changes are taking place in the oceans and in the cryosphere, some of which are irreversible, even if the most optimistic scenarios for reducing greenhouse gas emissions were to come true.
Allies in the face of climate change
As we have already seen, global warming is specially primed by the oceans, but the oceans can also be part of the solution. The oceans are known to function as a CO2 sink and have an enormous capacity to absorb CO2 - up to 31% of all anthropogenic CO2, according to a study published in the journal Science in 2019. They do not have that reputation, but the oceans are certainly the true lungs of the planet.
The authors of the paper recently published in the journal Advances in Atmospheric Sciences conclude that it is urgent to act because, if we do so, we can mitigate many of the negative effects of global warming. "The price we pay for the rise in ocean temperature is high: reduction of dissolved oxygen in the water, loss of marine biodiversity, increase in storms, reduction of fishing and of the economies that depend on the sea," reflects Lijing Cheng, a researcher at the Institute of Atmospheric Physics of the Chinese Academy of Sciences and lead author of the paper. "However, the more we reduce greenhouse gases, the less the ocean will be heated. The way forward is clear: reduce, reuse, recycle and make the transition to clean energy systems," he concludes.
Reference: Cheng et al. 2020. Record-Setting Ocean Warmth Continued in 2019. Advances in Atmospheric Sciences 37 (2) 137-142