New framework accounts for conflicting estimates of global temperature increases

July 5, 2017
Credit: CC0 Public Domain

Harvard University researchers have resolved a conflict in estimates of how much the Earth will warm in response to a doubling of carbon dioxide in the atmosphere.

That conflict—between temperature ranges based on and paleoclimate records and ranges generated from historical observations—prevented the United Nations' Intergovernmental Panel on Climate Change (IPCC) from providing a best estimate in its most recent report for how much the Earth will warm as a result of a doubling of CO2 emissions.

The researchers found that the low range of temperature increase—between 1 and 3 degrees Celsius—offered by the historical observations did not take into account long-term patterns. When these patterns are taken into account, the researchers found that not only do temperatures fall within the canonical range of 1.5 to 4.5 degrees Celsius but that even higher ranges, perhaps up to 6 degrees, may also be possible.

The research is published in Science Advances.

It's well documented that different parts of the planet warm at different speeds. The land over the , for example, warms significantly faster than water in the Southern Ocean.

"The historical pattern of warming is that most of the warming has occurred over land, in particular over the northern hemisphere," said Cristian Proistosescu, PhD '17, and first author of the paper. "This pattern of warming is known as the fast mode—you put CO2 in the atmosphere and very quickly after that, the land in the northern hemisphere is going to warm."

But there is also a slow mode of warming, which can take centuries to realize. That warming, which is most associated with the Southern Ocean and the Eastern Equatorial Pacific, comes with positive feedback loops that amplify the process. For example, as the oceans warm, cloud cover decreases and a white reflecting surface is replaced with a dark absorbent surface.

The researchers developed a mathematical model to parse the two different modes within different models.

"The models simulate a warming like today's, but indicate that strong feedbacks kick in when the Southern Ocean and Eastern Equatorial Pacific eventually warm, leading to higher overall temperatures than would simply be extrapolated from the warming seen to date," said Peter Huybers, Professor of Earth and Planetary Sciences and of Environmental Science and Engineering at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and co-author of the paper.

Huybers and Proistosescu found that while the slow mode of warming contributes a great deal to the ultimate amount of , it is barely present in present-day warming patterns. "Historical observations give us a lot of insight into how climate changes and are an important test of our ," said Huybers, "but there is no perfect analogue for the changes that are coming."

Explore further: Models, observations not so far apart on planet's response to greenhouse gas emissions

More information: C. Proistosescu el al., "Slow climate mode reconciles historical and model-based estimates of climate sensitivity," Science Advances (2017). DOI: 10.1126/sciadv.1602821 , http://advances.sciencemag.org/content/3/7/e1602821

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aksdad
1 / 5 (3) Jul 06, 2017
Uh huh. Suuure. It couldn't be something so simple as the climate models being wrong because they don't completely and accurately model all the non-linear, linked chaotic processes that influence climate. Naaah. They just need a tiny bit of tweaking and they'll be good.

So far they have utterly failed to even come close to predicting global temperatures. All the models overstate warming. Even the IPCC noticed this in their Fifth Assessment report in 2013. See here:

https://www.ipcc....S-14.jpg
Da Schneib
5 / 5 (3) Jul 06, 2017
It is the nature of physical models that they become more and more accurate over time. This is both because more information becomes available, and more and more work is done to make the model as close as possible to observation. This is how real science gets done. Hey, don't knock it, it invented transistors, didn't it? Not to mention refrigerators and jet aircraft.

Just sayin'.

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