Tropics are widening as predicted by climate models, research finds

Tropics are widening as predicted by climate models, research finds
Australia's Lake Hume is on the fringes of the tropics and could be affected by the expansion of desert areas associated with widening of the tropics.  Credit: Tim J. Keegan

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 .
  • 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 and pollution continue to increase, they write, human causes will become more obvious.


Explore further

Climatologists offer explanation for widening of tropical belt

More information: Paul W. Staten et al, Re-examining tropical expansion, Nature Climate Change (2018). DOI: 10.1038/s41558-018-0246-2
Journal information: Nature Climate Change

Provided by Indiana University
Citation: Tropics are widening as predicted by climate models, research finds (2018, September 17) retrieved 20 May 2019 from https://phys.org/news/2018-09-tropics-widening-climate.html
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Sep 17, 2018
Where are the Anti-Science Republican scumbags who claim that Global Warming isn't happening and that the Earth is actually cooling?


Sep 18, 2018
Sad... old rightwing climate deniers losing their marbles slowly on phys.org I suspect.

Sep 18, 2018
I was also waiting for the 7000 comments with "No it's not 'cause it's just not also soy boys, socialists, Gore something something, money, Jesus, I'm totally a Russian, LIES".
It's almost disappointing.

Sep 19, 2018
I was also waiting for the 7000 comments with "No it's not 'cause it's just not also soy boys, socialists, Gore something something, money, Jesus, I'm totally a Russian, LIES".
It's almost disappointing.....HAWW...HEE....HAWW..HEE

The leetenant jackass brays again.
This is the Chicken Little jackass who boasted about his, CO2 spewing, pleasure cruise to watch the ice in the Antarctic and his plans to do the same to the Arctic. Then, blind to his hypocrisy, he has the audacity to come here and pretend that he cares, by braying at the heretics.
Now. that's NOT almost disappointing......RIGHTTTT JACKASS.

Sep 19, 2018
Well @leetennant, you did just get called a chicken little jackass by an anti-Al Gore type. So at least you got something out of it.haha. I guess as long as nature is agreeing with all of our science models the poor science numb individuals can only complain bitterly when they are wrong (and they know that), So my good friend anti-Al Gore just needs to sharpen his pencils a little bit so that he can tackle his first-grade homework with those big thick first grade pencils.

Sep 20, 2018
Well @leetennant, you did just get called a chicken little jackass by an anti-Al Gore type. So at least you got something out of it.haha. I guess as long as nature is agreeing with all of our science models the poor science numb individuals can only complain bitterly when they are wrong (and they know that), So my good friend anti-Al Gore just needs to sharpen his pencils a little bit so that he can tackle his first-grade homework with those big thick first grade pencils.


Did I? I muted him a loooong time ago.
*runs off to read to some AG comments*
OMG, dude is obsessed with me! Half his recent comments are about me. Anti-G my friend, I just don't feel that way about you. Let's just be friends. It's not me, it's you.

Sep 20, 2018
Well @leetennant, you did just get called a chicken little jackass by an anti-Al Gore type. So at least you got something out of it.haha. I guess as long as nature is agreeing with all of our science models the poor science numb individuals can only complain bitterly when they are wrong (and they know that), So my good friend anti-Al Gore just needs to sharpen his pencils a little bit so that he can tackle his first-grade homework with those big thick first grade pencils...HAWW...HEE...HAWW....HEE...

howhot3..AKA...howShat da Turd, brays again.
This is the jackass who boasts that he knows the "science", yet he rode into NYC, spewing CO2 all the way, just to get a sniff of the methane from his False "Profit", Al Gore's rectum and pretend to care for the planet.

Sep 21, 2018
Nearly did a spit take with my coffee, leetennant. That is hilarious.

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