1 Nov 2018 - BBC News - The world has seriously underestimated the amount of heat soaked up by our oceans over the past 25 years, researchers say. Their study suggests that the seas have absorbed 60% more than previously thought. They say it means the Earth is more sensitive to fossil fuel emissions than estimated. This could make it much more difficult to keep global warming within safe levels this century.
What have the researchers found?
According to the last major assessment by the Intergovernmental Panel on Climate Change (IPCC), the world's oceans have taken up over 90% of the excess heat trapped by greenhouse gases.
But this new study says that every year, for the past 25 years, we have put about 150 times the amount of energy used to generate electricity globally into the seas - 60% more than previous estimates.
That's a big problem.
Scientists base their predictions about how much the Earth is warming by adding up all the excess heat that is produced by the known amount of greenhouse gases that have been emitted by human activities.
This new calculation shows that far more heat than we thought has been going into oceans. But it also means that far more heat than we thought has been generated by the warming gases we have emitted.
Therefore more heat from the same amount of gas means the Earth is more sensitive to CO2.
What are the implications of the finding?
The researchers involved in the study believe the new finding will make it much harder to keep within the temperature rise targets set by governments in the Paris agreement. Recently the IPCC spelled out clearly the benefits to the world of keeping below the lower goal of 1.5C relative to pre-industrial levels.
This new study says that will be very difficult indeed.
"It is a big concern," said lead author Dr Laure Resplandy from Princeton University in New Jersey.
"If you look at the IPCC 1.5C, there are big challenges ahead to keep those targets, and our study suggests it's even harder because we close the window for those lower pathways."
The report suggests that to prevent temperatures rising above 2C, carbon emissions from human activities must be reduced by 25% more than previously estimated.
What does it mean for the oceans?
As well as potentially making it more difficult to keep warming below 1.5 or even 2C this century, all that extra heat going into the oceans will prompt some significant changes in the waters.
"A warmer ocean will hold less oxygen, and that has implications for marine ecosystems," said Dr Resplandy.
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