PARIS, FRANCE —
The world's oceans were the warmest in recorded history in 2019, scientists said on Tuesday, with man-made emissions warming the seas at an ever-increasing rate, with potentially disastrous impacts on Earth's climate.
Oceans absorb over 90% of the excess heat created by greenhouse gas emissions and quantify how much they have warmed in recent years, giving scientists an accurate reading of the global warming rate.
A team of experts from around the world analyzed data compiled by China's Institute of Atmospheric Physics (IAP) to get a clear picture of ocean heat at a depth of 2,000 meters over several decades.
They found that the oceans last year were by far the warmest ever recorded and said the effects of ocean warming were already being felt in the form of more extreme weather, rising sea levels and damage to marine life.
The study, published in Advances in Atmospheric Sciences Magazine, said last year the ocean was 0.075 Celsius warmer than the historical average between 1981-2010.
This means that the world's oceans have absorbed 228 Zetta Joules (228 billion trillion Joules) of energy in recent decades.
"Too many zeros," said Cheng Lijing, lead author of the article and associate professor at IAP's International Center for Climate and Environmental Sciences.
"The amount of heat we have placed in the world's oceans over the past 25 years is equal to 3.6 billion atomic bomb explosions in Hiroshima."
The last five years are the warmest five years to the ocean, according to the study.
In addition to the medium-term warming trend, the data showed that the ocean absorbed 25 additional Zetta Joules in 2019 compared to 2018.
"This is roughly equivalent to everyone on the planet who uses one hundred hair dryers or one hundred microwaves continuously throughout the year," Michael Mann, director of Penn State's Earth System Sciences Center, told AFP.
– Centuries of warming –
The 2015 Paris agreement aims to limit global temperature rises to "well below" 2 ° C and to 1.5 ° C if possible.
With only 1 ° C of warming since the preindustrial period, Earth experienced a cascade of droughts, superstorms, floods and forest fires, most likely due to climate change.
The study's authors said there was a clear link between climate-related disasters – such as the fires that have been plaguing southeast Australia for months – and warming ocean.
Warmer seas mean more evaporation, Mann said.
"This means more rainfall but also more evaporative demand from the atmosphere," he said.
"This, in turn, leads to drying of the continents, a major factor behind recent forest fires from the Amazon to the Arctic, including California and Australia."
Warmer oceans also expand, leading to rising sea levels.
The United Nations Intergovernmental Panel on Climate Change, in a major report on oceans last year, warned that tens of millions could be displaced from coastal areas by the end of the century because of the invasion of the seas.
And given that the ocean has a much higher heat absorption capacity than the atmosphere, scientists believe they will continue to warm up even if humanity can reduce its emissions according to the Paris goals.
"As we continue to heat the planet with carbon emissions, we expect about 90% of the warming to continue to go to the oceans," said Mann.
"If we stop warming the planet, heat will continue to diffuse into the depths of the ocean for centuries until eventually it stabilizes."