The world's oceans hit their warmest level in recorded history in 2019, according to a study published Monday that provides more evidence that Earth is warming at an accelerated pace.
The analysis, which also found that ocean temperatures in the last decade have been the warmest on record, shows the impact of human-caused warming on the planet's oceans and suggests that sea-level rise, ocean acidification and extreme weather events could worsen as the oceans continue to absorb so much heat.
"The pace of warming has increased about 500 percent since the late 1980s," said one of the study's authors, John Abraham, a professor of thermal sciences at the University of St. Thomas in St. Paul, Minnesota. "The findings, to be honest, were not unexpected. Warming is continuing, it has accelerated, and it is unabated. Unless we do something significant and quickly, it's really dire news."
Abraham and his colleagues found that the rate of ocean warming accelerated from 1987 to 2019 to nearly 4½ times the rate of warming from 1955 to 1986.
According to the study, published Monday in the journal Advances in Atmospheric Sciences, average ocean temperatures in 2019 were 0.075 degrees Celsius (0.135 degrees Fahrenheit) above the 1981-2019 average. While that may seem minuscule, it represents an enormous amount of heat spread out across the world's oceans, according to the study's lead author, Lijing Cheng, an associate professor at the Institute of Atmospheric Physics in Beijing.
"The amount of heat we have put in the world's oceans in the past 25 years equals to 3.6 billion Hiroshima atom bomb explosions," Cheng said in a statement.
The study, conducted by an international team of 14 scientists, found that oceans have absorbed more than 90 percent of the heat trapped on Earth from greenhouse gas emissions since 1970.
"Oceans are the biggest reservoir of heat and therefore the best indicator of climate change," Abraham said. "If you want to know how fast the Earth is warming, look at the oceans."
Scientists are worried by the trend because warmer oceans can increase severe weather and intensify storms.
"It's like putting weather on steroids," Johnson said. "We did a study a few years ago that showed Hurricane Harvey in Texas passed over a very warm body of water, and that greatly increased the amount of rainfall."
Harvey unleashed more than 60 inches of rain over southeastern Texas in 2017, and scientists have said climate change will make storms rainier overall.
Warmer oceans also expand and melt ice, speeding the rise in sea levels and increasing the risk to coastal communities and low-lying infrastructure, said Nick Bond, a professor of atmospheric sciences at the University of Washington in Seattle, who wasn't involved with the new study. According to the U.N. Intergovernmental Panel on Climate Change, average global sea levels could rise by 0.95 feet to 3.61 feet by the end of the century.
"From Miami Beach to Bangladesh — as sea levels continue to creep up, it's just going to become less viable to live in these places," Bond said.
He added that there are other significant societal implications, such as the effect that warming oceans may have on the chemistry and biology of the world's oceans.
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When carbon dioxide is absorbed and mixes with ocean water, chemical reactions make the water more acidic. Some sea creatures and ecosystems, such as corals, struggle with this type of acidification, but Bond said scientists don't yet know the extent of the potential fallout.
"There are going to be winners and losers, but we don't know how that will all play out," he said. "It's a very complicated system, and we don't fully understand which species will have to shift their range, which ones may go extinct or which ones may prosper."
Katie Matthews, chief scientist at Oceana, an ocean conservation organization in Washington, D.C., said ocean warming could have enormous impacts on fisheries around the world, particularly in the tropics.
"The tropics are the areas that have the largest number of people reliant on fish for nutrition, food security and livelihood," she said. "It's really unfortunate that the most vulnerable and at-risk populations are going to be the ones most affected."
The study, which incorporated measurements from the National Oceanic and Atmospheric Administration, used data on ocean temperatures dating to the 1950s. The measurements included recordings of temperatures extending from the sea surface to depths of more than 6,500 feet.
Average ocean temperatures over the years have followed the warming trend, but Abraham said some of the most pronounced warming has taken place in the South Atlantic Ocean, in the Pacific Ocean off the coast of Japan, and in the waters south of Australia.
Abraham said he hopes the findings will spark climate action around the world.
"This isn't a political issue," he said. "This is a science issue, and our measurements are telling us that this is a problem and we need to take action."