The world’s oceans were the hottest ever recorded in 2022, demonstrating the profound and widespread changes that human-caused emissions have wrought on the planet’s climate.
More than 90% of the excess heat trapped by greenhouse gas emissions is absorbed by the oceans. Records, beginning in 1958, show an inexorable rise in ocean temperatures, with warming accelerating after 1990.
Sea surface temperatures are a major influence on global climate. Warmer oceans help fuel extreme weather, leading to more intense hurricanes and typhoons, and more moisture in the air, leading to more intense rain and flooding. The warmer water is also expanding, raising sea levels and endangering coastal cities.
The temperature of the oceans is much less affected by natural climate variability than the temperature of the atmosphere, making the oceans an undeniable indicator of global warming.
Last year is expected to be the fourth or fifth warmest on record for surface air temperatures when final data is collated. During 2022, we saw the third consecutive La Niña event, which is the coldest phase of an irregular Pacific-centered weather cycle that affects global weather patterns. When El Niño returns, global air temperatures will rise even more.
The international team of scientists that produced the new analysis of ocean heat concluded: “Earth’s water and energy cycles have been profoundly disrupted due to the emission of greenhouse gases from human activities, leading to widespread changes in the Earth’s climate system.
Professor John Abraham, from the University of St Thomas in Minnesota and part of the study team, said: “If you want to measure global warming, you have to measure where the warming is going, and over 90% of it goes to the oceans.
“Measuring the oceans is the most accurate way to determine how out of balance our planet is.
“We are having more extreme weather because of the warming of the oceans, and that has tremendous consequences around the world.”
Professor Michael Mann, from the University of Pennsylvania, also part of the team, said: “Warmer oceans mean there is more potential for larger precipitation events, as we have seen in the past year in Europe, Australia and currently off the coast. west”. from United States.”
He said the analysis showed a deeper and deeper layer of warm water at the ocean surface: “This leads to more and more rapid intensification of hurricanes, something we’ve also seen in the past year as the winds no longer stir cold underground. surface water that would otherwise buffer intensification.”
Research published Monday by the US National Oceanic and Atmospheric Administration showed that many extreme weather events in 2022 they had been made more likely and intense by the climate crisis, such as the heavy rains that caused devastating floods in Chad, Niger and Nigeria.
Reliable measurements of ocean temperature date back to 1940, but it is likely that the oceans are now at their hottest in 1,000 years and warming faster than at any time in the last 2,000 years.
The analysis, published in the journal Advances in Atmospheric Sciencesit used temperature data collected by a variety of instruments in the oceans and combined separate analyzes from Chinese and US teams to calculate the heat content of the upper 2,000 meters, where most of the warming occurs.
The oceans absorbed about 10 zettajoules more heat in 2022 than in 2021, which is equivalent to every person on Earth using 40 hair dryers all day, every day.
The researchers also looked at salinity, which along with temperature determines the density of water and is a vital driver of ocean circulation. An index of salinity variability in the oceans hit a record in 2022, showing a continued amplification of the global hydrological cycle.
Another important feature of the oceans is stratification, where the stratification of water by density becomes stronger. This restricts the mixing of deeper, cooler, nutrient-rich waters with surface waters.
The long-term trend of increasing stratification continued in 2022, according to the scientists, with “important scientific, social and ecological consequences.”
One consequence, Abraham said, is that less mixing in the ocean means the surface layer absorbs less carbon dioxide from the atmosphere, increasing global warming.
The researchers also said: “There are more and more record-breaking heat waves and droughts in the Northern Hemisphere, consistent with intense ocean warming in the mid-latitude Pacific and Atlantic oceans.”
Ocean warming and extreme weather impacts will increase until humanity reaches net zero emissions.
In October, the World Meteorological Organization reported that the atmospheric concentration of all major greenhouse gases: carbon dioxide, methane and nitrous oxide – had reached record levels. WMO chief Professor Petteri Taalas said: “We are going in the wrong direction.”