Climate change: Oceans have gone up 60% more heat than estimated

Researchers say that the world has seriously underestimated the amount of heat soaked up by our oceans over the past 25 years.

Their new studies show that they 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.

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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 been around 150 times the amount of energy used to generate electricity globally in the world – 60% more than previous estimates.

That's a big problem.

Scientists base their predictions on how much the earth is warming up by adding up 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 think has been going into the oceans. But it also means that we are more excited by the warming gases we have emitted.

Therefore more heat from the earth is more sensitive to CO2.

What are the implications of finding?

The researchers involved in the study believe that it will be much easier to meet the target audience in the Paris agreement. Recently, the IPCC has clearly shown the benefits of 1.5C relative to pre-industrial levels.

This new study says that it will be very difficult indeed.

"It is a big concern," said lead author Dr. Laure Resplandy from Princeton University in New Jersey, US.

"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?

It is more important to keep warming than 1.5 or even 2C this century, all that extra heat going into the oceans.

"A warmer ocean will hold less oxygen," said Dr. Resplandy.

"There is also a need for more sea level expansion and more sea level rise."

What do these scientists do differently?

Since 2007, scientists have been able to rely on a system of almost 4,000 Argo floats that record temperature and salinity in the oceans around the world.

But prior to this, the methods used to measure the heat in the ocean had many flaws and uncertainties.

Now, researchers have developed what they say is a highly accurate method of detecting the temperature of the ocean by measuring the amount of oxygen and carbon dioxide in the air. This allows for global measurement of global data, dating back to 1991, when accurate data from a global network of stations became available.

The key element is the fact that the waters get warmer they release more carbon dioxide and oxygen into the air.

"When the ocean warms, the amount of these gases that the ocean is able to hold goes down," said Dr. Resplandy.

"So what we measured was the amount lost by the oceans, and then we can calculate how much warming we need to explain that change in gases."

Will the heat ever come back out?

Yes, say the authors, but over a very long time.

"The heat stored in the ocean will eventually come back to us," said Dr. Resplandy.

"The fact that the ocean holds so much heat that it can be used in the future.

"The ocean circulation that controls the ocean heat uptake / release operates on time scales of centuries, meaning that ocean heat would be released for the centuries to come."

How have other people responded to the findings?

With some concern.

"The authors have a very strong track record and very solid reputation, however, which lends the story credibility," said Prof Sybren Drijfhout at the UK's National Oceanography Center in Southampton.

"The expectations are as likely to be as likely to be as society can meet 1.5 and 2 degree targets as it shifts the lower bound of climate sensitivity upward."

Others say that further work is required.

"The uncertainty in the ocean is still large, even when using this new independent method, which also has uncertainties," said Thomas Froelicher from the University of Bern, Switzerland.

"The conclusion on a potential higher temperature sensitivity and possible less carbon emissions 2C should stimulate further investigation."

The study has been published in the journal Nature.