Nav: Home

Tropics are widening as predicted by climate models, research finds

September 17, 2018

BLOOMINGTON, Ind. -- Scientists have observed for years that the Earth's tropics are widening in connection with complex changes in climate and weather patterns. But in recent years, it appeared the widening was outpacing what models predicted, suggesting other factors were at work.

A new paper co-authored by Indiana University Bloomington researcher Paul Staten, however, finds that the most up-to-date models and the best data match up reasonably well.

"If we compare the observed trends of how the tropics have widened to modeling trends, it's actually not outside of what the models predict," said Staten, assistant professor of atmospheric sciences in the College of Arts and Sciences.

Staten is an affiliated researcher with the IU Environmental Resilience Institute, which was established under Prepared for Environmental Change, the second initiative funded by the university's Grand Challenges Program.

The paper, "Re-examining Tropical Expansion," was published in the journal Nature Climate Change. Additional authors include Jian Lu of the Pacific Northwest National Laboratory, Kevin Grise of the University of Virginia, Sean Davis of the National Oceanic and Atmospheric Administration in Colorado and Thomas Birner of Ludwig Maximilians University Munich in Germany.

Staten said the research should add confidence to predictions based on current climate models.

"Climate change should continue to expand the tropics over the next several decades," he said. "But the expansion may not continue at the rapid rate we've seen; at times it may even temporarily contract."

The authors conclude that the tropics have been widening at an average rate of about 0.2 degrees latitude, or about 17 miles, per decade in both the Northern and Southern hemispheres. The rate varies widely from year to year and from location to location.

Widening of the tropics is important because it could be associated with severe changes in climate, Staten said. The world's hot, dry deserts tend to be located in bands along the northern and southern edges of the tropics, so widening of the tropics could lead to expansion of the subtropical deserts. At sea, the edges of the tropics are zones of high salinity and low marine productivity.

About half of the world's population lives in or near subtropical semi-arid climate zones, the researchers write, so changes in the subtropical climate could affect billions of people.

The researchers focus on five factors that may influence the widening of the tropics:
  • Increases in greenhouse gas emissions, which lead to a warmer global climate.
  • Depletion of ozone in the stratosphere over the South Pole, which probably shifts the edge of the tropics, especially in the Southern Hemisphere.
  • Aerosols from volcanic eruptions.
  • Pollution, including soot and ozone in the troposphere.
  • Natural variation, including changes in sea surface temperatures tied to the El Niño and La Niña phenomena.
Given the complexity of the factors, the authors say, it is difficult for now to tease out differences in natural and human-caused influences on the widening of the tropics. But if greenhouse gas emissions and pollution continue to increase, they write, human causes will become more obvious.
-end-


Indiana University

Related Climate Change Articles:

Fairy-wrens change breeding habits to cope with climate change
Warmer temperatures linked to climate change are having a big impact on the breeding habits of one of Australia's most recognisable bird species, according to researchers at The Australian National University (ANU).
Believing in climate change doesn't mean you are preparing for climate change, study finds
Notre Dame researchers found that although coastal homeowners may perceive a worsening of climate change-related hazards, these attitudes are largely unrelated to a homeowner's expectations of actual home damage.
Older forests resist change -- climate change, that is
Older forests in eastern North America are less vulnerable to climate change than younger forests, particularly for carbon storage, timber production, and biodiversity, new research finds.
Could climate change cause infertility?
A number of plant and animal species could find it increasingly difficult to reproduce if climate change worsens and global temperatures become more extreme -- a stark warning highlighted by new scientific research.
Predicting climate change
Thomas Crowther, ETH Zurich identifies long-disappeared forests available for restoration across the world.
Historical climate important for soil responses to future climate change
Researchers at Lund University in Sweden, in collaboration with colleagues from the University of Amsterdam, examined how 18 years of drought affect the billions of vital bacteria that are hidden in the soil beneath our feet.
Can forests save us from climate change?
Additional climate benefits through sustainable forest management will be modest and local rather than global.
From crystals to climate: 'Gold standard' timeline links flood basalts to climate change
Princeton geologists used tiny zircon crystals found in volcanic ash to rewrite the timeline for the eruptions of the Columbia River flood basalts, a series of massive lava flows that coincided with an ancient global warming period 16 million years ago.
Think pink for a better view of climate change
A new study says pink noise may be the key to separating out natural climate variability from climate change that is influenced by human activity.
Climate taxes on agriculture could lead to more food insecurity than climate change itself
New IIASA-led research has found that a single climate mitigation scheme applied to all sectors, such as a global carbon tax, could have a serious impact on agriculture and result in far more widespread hunger and food insecurity than the direct impacts of climate change.
More Climate Change News and Climate Change Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

Risk
Why do we revere risk-takers, even when their actions terrify us? Why are some better at taking risks than others? This hour, TED speakers explore the alluring, dangerous, and calculated sides of risk. Guests include professional rock climber Alex Honnold, economist Mariana Mazzucato, psychology researcher Kashfia Rahman, structural engineer and bridge designer Ian Firth, and risk intelligence expert Dylan Evans.
Now Playing: Science for the People

#540 Specialize? Or Generalize?
Ever been called a "jack of all trades, master of none"? The world loves to elevate specialists, people who drill deep into a single topic. Those people are great. But there's a place for generalists too, argues David Epstein. Jacks of all trades are often more successful than specialists. And he's got science to back it up. We talk with Epstein about his latest book, "Range: Why Generalists Triumph in a Specialized World".
Now Playing: Radiolab

Dolly Parton's America: Neon Moss
Today on Radiolab, we're bringing you the fourth episode of Jad's special series, Dolly Parton's America. In this episode, Jad goes back up the mountain to visit Dolly's actual Tennessee mountain home, where she tells stories about her first trips out of the holler. Back on the mountaintop, standing under the rain by the Little Pigeon River, the trip triggers memories of Jad's first visit to his father's childhood home, and opens the gateway to dizzying stories of music and migration. Support Radiolab today at Radiolab.org/donate.