According to research, 2014 marked the “point of no return” for extreme heat in the world's oceans, and has now become the new normal level.
Scientists analysed sea surface temperatures from the last 150 years and found that extreme temperatures occurring only 2% of the time a century ago, have now occurred at least 50% of the time across the global ocean since 2014, with some hot spots seeing a 90% occurrence, which has severely affected wildlife.
The ocean plays a critical role in maintaining a stable climate, with more than 90% of the heat trapped by greenhouse gases absorbed by the ocean.
Monterey Bay Aquarium employee and one of the research team, Kyle Van Houtan, said "By using this measure of extremes, we’ve shown that climate change is not something that is uncertain and may happen in the distant future – it’s something that is a historical fact and has occurred already".
"Extreme climate change is here, it’s in the ocean, and the ocean underpins all life on Earth".
Both Van Houtan and colleague Kisei Tanaka are ecologists, who began the study because they wanted to assess how heat extremes were related to the loss of kelp forests off the coast of California.
"Ecology teaches us that extremes have an outsized impact on ecosystems", Van Houtan said, "we are trying to understand the dramatic changes that we’ve seen along our coasts and in the ocean, on coral reefs, kelp, white sharks, sea otters, fish, and more.”
In 2019, other scientists reported that the number of heat waves affecting the planet's oceans had sharply increased, resulting in swathes of sea life being killed like "wildfires that take out huge areas of forest".
When researching, Van Houtan and Tanaka found that no measure of extreme heat existed, and so they extended their work globally. The final study, published in the Plos Climate Journal, examined the monthly temperature in each one-degree-by-one-degree part of the ocean, and set up the highest temperature in the 50 year period as the benchmark for extreme heat.
They then examined temperature records from 1920 to 2019 and discovered that by 2014, more than 50% of the monthly records across the entire ocean had surpassed their set-up benchmark. The researchers claimed the year when the percentage passed 50% and did not fall below it as the "point of no return".
The proportion of the global ocean suffering extreme heat by 2019 was 57% and Van Houtan expect this to keep on going up, though they noted that the extreme heat was particularly severe in some parts of the ocean. The South Atlantic passed this "point of no return" in 1998.
The proportion of the ocean that is experiencing the extreme heat in some large ecosystems is now 80% to 90%. The five worst affected includes areas off the North East coasts of both the US and Canada, off Somalia and Indonesia, and in the Norwegian Sea.
Commenting on the 14 fisheries in Alaska who have recently been declared federal disasters, Van Houtan said: "You should care about turtles, seabirds and whales, but even if you don’t, the two most lucrative fisheries in the US, lobster and scallops, are in those exact spots".
The heat content on the top 2,000 metres of the ocean set a new record in 2021 for the sixth year in a row. One of the team behind the assessment, Professor John Abraham at the University of St Thomas in Minnesota, said that the ocean heat content was the most relevant to the global climate, while surface temperatures were most relevant to weather patterns.
He added: "Oceans are critical to understanding climate change. They cover about 70% of the planet’s surface and absorb more than 90% of global warming heat. The new study is helpful because the researchers look at the surface temperatures. It finds there has been a big increase in extreme heat at the ocean’s surface and that the extremes are increasing over time".
