New framework accounts for conflicting estimates of global temperature increases

July 5, 2017, Harvard John A. Paulson School of Engineering and Applied Sciences
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 ,

Related Stories

Historical records miss a fifth of global warming: NASA

July 22, 2016

A new NASA-led study finds that almost one-fifth of the global warming that has occurred in the past 150 years has been missed by historical records due to quirks in how global temperatures were recorded. The study explains ...

Cloudy feedback on global warming

October 31, 2016

Lawrence Livermore National Laboratory researchers have identified a mechanism that causes low clouds - and their influence on Earth's energy balance - to respond differently to global warming depending on their spatial pattern.

Recommended for you

Sahara dust may make you cough, but it's a storm killer

July 20, 2018

The bad news: Dust from the Sahara Desert in Africa—totaling a staggering 2 to 9 trillion pounds worldwide—has been almost a biblical plague on Texas and much of the Southern United States in recent weeks. The good news: ...

Human influence detected in changing seasons

July 20, 2018

For the first time, scientists from Lawrence Livermore National Laboratory (LLNL) and five other organizations have shown that human influences significantly impact the size of the seasonal cycle of temperature in the lowest ...


Adjust slider to filter visible comments by rank

Display comments: newest first

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:

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'.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.