Not only on land, but also in the world’s oceans, global warming is causing new maximum temperatures. Compared to the 1981-2010 average, ocean heat has increased by over 200 zettajoules. Because the oceans absorb more than 90 percent of the excess heat that accumulates in the climate system.
An international team of 24 scientists evaluated data from the US climate agency NOAA and the Institute for Atmospheric Physics of the Chinese Academy of Sciences (CAS). The values for 2022 continue the steady increase in sea temperatures: Since the 1980s, the heat content in the seas has been increasing particularly sharply, and the rate of warming has at least tripled since then.
The authors write that this is due to the increasing concentration of greenhouse gases: “The inexorable rise in sea temperatures is the inevitable result of the energy imbalance on earth, driven by greenhouse gas emissions,” according to the study, which is published in the journal “Advances in Atmospheric Sciences” was published.
Central measurement of the greenhouse effect
The records of the heat content of the oceans form a central measurement for recording the climate crisis, because the ocean heat content is less influenced by internal climate fluctuations, the researchers explain in the study. “It’s a parameter from which the man-made greenhouse effect can be read even better than from the temperature of the earth’s surface,” explains Leopold Haimberger from the Institute for Meteorology and Geophysics at the University of Vienna.
In addition to heat content, salinity is also a key parameter for measuring how the climate crisis is affecting the oceans and vice versa. In the course of the study, the researchers also found that regions that already have a high salt content become even saltier. Conversely, regions that are less saline lose salt concentration.
Feedback effect from ocean stratification
The warming and salinization of the seas, in turn, has a significant impact on the exchange of heat, oxygen and carbon dioxide with the atmosphere. Normally, there is a regular exchange of water masses, cold water sinks, warm water rises. Due to the warming, layers are formed in the seas, the water no longer mixes.
This leads to a kind of feedback effect: the surface temperature rises, causing the atmosphere to warm up as well. The stratification triggered by climate change reinforces this additionally. From 1960 to 2018, this stratification of the oceans increased by more than five percent.
In addition to the heat, the oceans also absorb around a third of the additional carbon dioxide from the atmosphere – not without impacting marine ecosystems such as coral reefs. Because only a few corals survive such an increased concentration of CO2, by the year 2035 half of all coral reefs could be gone.
More rain, less snow
In general, the sea is losing oxygen, according to the study. This is “a nightmare, not only for life and ecosystems in the sea, but also for people and our ecosystems on land,” explain the researchers involved. For a quarter of humanity, 2022 was the warmest year since records began, as determined by the European earth observation program Copernicus.
Due to rising sea temperatures, extreme weather events are also increasing – and this also in Austria. “If the upper water layers warm up, more water can evaporate, and that in turn means more intense precipitation events,” Haimberger said in an interview with ORF.at. In Austria, too, the Mediterranean Sea, the Baltic Sea and the Atlantic are not far away.
The warming of the oceans also has an indirect effect on the snow line: “When the oceans are warm, the air above tends to be warmer too. The air masses bringing precipitation that are brought to the Alps are therefore warmer, and then the precipitation tends to fall as rain up to higher layers,” Haimberger outlines.
The fact that warmer water means that less carbon dioxide can be stored in the ocean basically affects all countries, including Austria: “When the ocean is warm, it can absorb less carbon dioxide, which increases the effects of CO2 emissions,” says the expert .
What happens when the energy storage tips over
At some point, climate changes – on land and at sea – could lead to unstoppable chain reactions that would increase global warming uncontrollably. Because different regions and ecosystems that are in danger of tipping over are closely linked. These climate tipping points describe the irreversible effects of global warming on the climate system. As soon as a tipping point of a system is exceeded, the system rearranges itself – including the air conditioning system.
As a store of energy and CO2, the ocean is, so to speak, the motor and mediator of the climate. Warmer oceans are also directly related to sea level rise, and the volume of the sea expands as a result of warming. But the melting of ice bodies is also promoted by the heat of the sea. The slowing of the Atlantic overturning current and the coral die-off are also directly related to global warming.
“Greenland, for example, is of course also massively affected by the warming of the oceans,” says Haimberger. Warmer water near the island means it rains more often, causing the ice to melt faster. “It’s the same with glaciers,” adds the expert.
Call for solidarity in all areas
According to the International Union for Conservation of Nature (IUCN), around eight percent of the ocean is currently covered by marine protected areas. The High Seas in particular are often interpreted as a legal vacuum, writes the Climate Change Center Austria (CCCA) in a press release. There is a gap between countries in the global north and south – in many areas.
The USA, Germany, France, Great Britain, Japan and South Korea, for example, have the infrastructure and scientific data needed to manage marine protected areas and carry out environmental impact assessments. But the distribution of economic opportunities that result from this is also unequal – as is the state of research itself.
The South Atlantic, for example, has received only a fraction of the scientific attention that the North Atlantic has, writes Regina Rodrigues, professor of physical oceanography and climate at Brazil’s Santa Catarina University in Carbon Brief. Among other things, because the ocean is surrounded by countries with lower incomes that cannot finance the high costs of oceanographic research.
However, the South Atlantic directly affects the climate of many South American and African countries and can lead to extreme events such as heat waves, droughts and floods, leaving millions of people water and food insecure.
Changes in the oceans as a result of the climate crisis also go hand in hand with social issues. It is the poorest countries that contribute the least to global warming, but feel the effects most severely and earliest. As a landlocked country, Austria should therefore also show solidarity with the populations of countries directly affected by global warming, said Haimberger. Also because Austria is already experiencing global warming and sea heating with all its effects.
