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Climate change: Oceans 'soaking up more heat than estimated' Climate change: Concerns over report on ocean heating
(12 days later)
The world has seriously underestimated the amount of heat soaked up by our oceans over the past 25 years, researchers say. Errors have been found in a recent study suggesting the oceans were soaking up more heat than previously estimated.
Their study suggests that the seas have absorbed 60% more than previously thought. The initial report suggested 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. But a re-examination by a mathematician showed that the margin of error was larger than in the published study.
This could make it much more difficult to keep global warming within safe levels this century. The authors have acknowledged the problem and have submitted a correction to the journal.
What have the researchers found? What had the researchers initially claimed?
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. According to the last major assessment by the Intergovernmental Panel on Climate Change (IPCC), the world's oceans have taken up more than 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. But the new study claimed 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. The authors suggested that this had huge implications for the way that the world is warming.
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. If far more heat than previously believed was going into oceans, it also meant that far more heat than we thought has been generated by the warming gases we have emitted in the world to date.
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.Therefore more heat from the same amount of gas means the Earth is more sensitive to CO2.
What are the implications of the finding? What had these scientists done differently?
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.
"There is also sea level, if you warm the ocean more you will have more thermal expansion and therefore more sea level rise."
What have these scientists done 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.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.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 precise method of detecting the temperature of the ocean by measuring the amount of oxygen and carbon dioxide in the air. This allows them to accurately measure ocean temperatures globally, dating back to 1991, when accurate data from a global network of stations became available. The team involved in the study used a new approach to measuring the amount of oxygen and carbon dioxide in the air. They believed that this allowed them to accurately measure ocean temperatures globally, dating back to 1991, when data from a global network of stations became available.
The key element is the fact that as waters get warmer they release more carbon dioxide and oxygen into the air. The key element in this methodology is the fact that, as 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. "When the ocean warms, the amount of these gases that the ocean is able to hold goes down," said lead author Dr Laure Resplandy from Princeton University.
"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.""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? So how were the errors detected?
Yes, say the authors, but over a very long time. They were discovered by a mathematician, Nicholas Lewis, who has long been critical of climate models, arguing that they are over-sensitive to emissions of carbon dioxide.
"The heat stored in the ocean will eventually come back out if we start cooling the atmosphere by reducing the greenhouse effect," said Dr Resplandy. He reviewed the paper when it was published and found what he termed "serious (but surely inadvertent) errors in the underlying calculations."
"The fact that the ocean holds so much heat that can be transferred back to the atmosphere makes it harder for us to keep the Earth surface temperature below a certain target in the future. The key element deals with the amount of uncertainty in the measurements. As a result of the increased margin of error, the findings on the amount of heat being absorbed by the oceans can't be definitively supported.
"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 the authors reacted?
How have other scientists responded to the findings? They've put their hands up and acknowledged the error.
With some concern. Ralph Keeling, who co-authored the study said in a statement that he takes responsibility for the "oversights" and would like to "thank Nicholas Lewis for bringing an apparent anomaly in the trend calculation to our attention."
"The authors have a very strong track record and very solid reputation... which lends the story credibility," said Prof Sybren Drijfhout from the University of Southampton. "These problems do not invalidate the methodology or the new insights into ocean biogeochemistry on which it is based, but they do influence the mean rate of warming we infer, and more importantly, the uncertainties of that calculation."
"The updated estimate is indeed worrying in terms of how likely it is that society can meet 1.5 and 2 degree targets as it shifts the lower bound of climate sensitivity upward." The authors say they have now reworked their calculations and submitted a correction to the journal, Nature, which originally published the study.
Others say that further work is required. What have the publishers of the report said?
"The uncertainty in the ocean heat content change estimate is still large, even when using this new independent method, which also has uncertainties," said Thomas Froelicher from the University of Bern, Switzerland. They have issued an editor's note about the issue.
"The conclusion about a potential higher climate sensitivity and potentially less allowable carbon emission to stay below 2C should stimulate further investigation." "We would like to alert readers that the authors have informed us of errors in the paper. An implication of the errors is that the uncertainties in ocean heat content are substantially underestimated. We are working with the authors to establish the quantitative impact of the errors on the published results, at which point in time we will provide a further update."
The study has been published in the journal Nature. What does all this mean for ocean warming?
According to the scientists involved in the original study, the ocean is still probably warming more than the estimate used by the Intergovernmental Panel on Climate Change. But the errors mean that it has a larger range of probability - between 10% and 70%. This is in line with other studies.
"Our error margins are too big now to really weigh in on the precise amount of warming that's going on in the ocean," Ralph Keeling said. "We really muffed the error margins."
UPDATE: The original version of this story was published before the errors in the study came to light.