Warmer world may bring more local, less global, temperature variability

September 5, 2017, Duke University
A new study finds temperature variability will increase in some regions (shown in red) as Earth warms, even as global variability declines. Credit: Duke University, Nature Climate Change

Many tropical or subtropical regions could see sharp increases in natural temperature variability as Earth's climate warms over coming decades, a new Duke University-led study suggests.

These local changes could occur even though Earth's global mean surface air (GMST) is likely to become less variable, the study shows.

"This new finding runs counter to the popular notion that as the climate warms, will increase and weather will get more volatile everywhere," said Patrick T. Brown, a postdoctoral research scientist at the Carnegie Institution for Science, who led the study while he was a doctoral student at Duke's Nicholas School of the Environment.

"Our research suggests a different scenario: Global unforced temperature variability will actually decrease, not increase, as Earth warms, but local decade-to-decade variability could increase by as much as 50 percent in some places," Brown said.

Unforced, or natural, temperature variability can be caused by interactions between the atmosphere, ocean currents and sea ice. These fluctuations can either mask or exacerbate human-caused climate change for a decade or two at a time, he noted.

Because billions of people live in tropical or subtropical regions that may experience increased temperature variability, and because these regions are critical for biodiversity, food production and climate regulation, "it's vital that we understand the magnitude of unforced decade-to-decade variability that could occur there, and the mechanisms that drive it," he said.

Brown and his colleagues published their peer-reviewed paper Sept. 4 in the journal Nature Climate Change.

To conduct the study, they first inspected a climate model run under pre-industrial conditions. The model, which was developed at NOAA's Geophysical Fluid Dynamics Laboratory, simulates climate under perpetual atmospheric conditions similar to those experienced on Earth before the widespread emission of industrial greenhouse gasses. This allows scientists to get a clearer picture of the forces that cause variability in the absence of human drivers.

"To isolate unforced variability, we looked at the model's output without changing any of its environment parameters, such as atmospheric carbon dioxide levels, solar radiation or volcanic activity, over a theoretical 900-year timespan," Brown explained.

On the second run, the scientists doubled the model's atmospheric carbon dioxide levels to simulate projected future conditions.

"In the doubled-CO2 run, we saw a 43 percent decrease in global temperature variability, but with local increases of up to 50 percent in many land regions of the tropics and subtropics," Brown said.

Consistent results were obtained using similar experiments on other climate models.

What's happening, Brown said, is as Earth warms because of increasing CO2, there is less ice at high latitudes, which means less albedo - the less reflection of solar energy back into space.

"Albedo feedback is a large contributor to decade-to-decade unforced variability. When Earth's atmosphere naturally gets a bit warmer, more of the reflective sea ice at high latitudes melts. This exposes more water, which absorbs solar energy and amplifies the initial warming, enhancing the GMST variability," he explained. "But we found that when you double the CO2 levels in a climate model to mimic future conditions, the sea ice melts so much that this albedo feedback can no longer play a large role in amplifying natural temperature variability."

The end result is less variability globally - especially in the - but more variability in the tropics.

"This suggests that the pre-industrial control runs we have been using are not ideal for studying what unforced variability will look like in the future," said Wenhong Li, associate professor of at Duke's Nicholas School. "But it might inspire more modeling groups to run models under perpetual conditions that reflect what we expect in the future."

Explore further: Climate models disagree on why temperature 'wiggles' occur

More information: Patrick T. Brown et al, Change in the magnitude and mechanisms of global temperature variability with warming, Nature Climate Change (2017). DOI: 10.1038/nclimate3381

Related Stories

Climate models disagree on why temperature 'wiggles' occur

January 26, 2015

A new Duke University-led study finds that most climate models likely underestimate the degree of decade-to-decade variability occurring in mean surface temperatures as Earth's atmosphere warms. The models also provide inconsistent ...

Long-term global warming not driven naturally

February 1, 2016

By examining how Earth cools itself back down after a period of natural warming, a study by scientists at Duke University and NASA's Jet Propulsion Laboratory confirms that global temperature does not rise or fall chaotically ...

Central European summer temperature variability to increase

December 18, 2012

More extreme heat waves have been observed in central Europe in recent years as summer temperature variability has increased on both daily and interannual timescales. Models project that as the climate warms throughout the ...

Will temperature extremes increase in Northeast Asia?

November 4, 2016

Northeast Asia includes the areas of Northeast China, the Russian Far East, Japan and the Korean Peninsula. Climate variability and change impose enormous challenges for this region, with its rapidly developing economy and ...

Recommended for you

After a reset, Сuriosity is operating normally

February 23, 2019

NASA's Curiosity rover is busy making new discoveries on Mars. The rover has been climbing Mount Sharp since 2014 and recently reached a clay region that may offer new clues about the ancient Martian environment's potential ...

Study: With Twitter, race of the messenger matters

February 23, 2019

When NFL player Colin Kaepernick took a knee during the national anthem to protest police brutality and racial injustice, the ensuing debate took traditional and social media by storm. University of Kansas researchers have ...

Researchers engineer a tougher fiber

February 22, 2019

North Carolina State University researchers have developed a fiber that combines the elasticity of rubber with the strength of a metal, resulting in a tougher material that could be incorporated into soft robotics, packaging ...

2 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

omegatalon
1.8 / 5 (5) Sep 05, 2017
Given how old Earth is and what scientist at best are speculating, it's difficult to consider anything that scientists are saying now as being factual.
PTTG
4 / 5 (4) Sep 05, 2017
The final collapse of cognitive integrity: "I don't agree with what the experts say; therefore, the experts are wrong."

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.