ADVERTISEMENT
  About the SA Blog Network













Observations

Observations


Opinion, arguments & analyses from the editors of Scientific American
Observations HomeAboutContact

Soot May Help Shift Tropics North


Email   PrintPrint



tropicsSoot may be responsible for the tropics expanding north, according to an analysis involving multiple computer models of the climate. By absorbing sunlight and trapping extra heat in the atmosphere, the tiny, black particles may be helping the poleward march of tropical conditions.

The research will be published in Nature on May 17. (Scientific American is part of Nature Publishing Group.)

The tropics—the belt of land around the equator characterized by abundant rainfall and torrid temperatures —have been expanding for at least 40 years. In fact, the tropics have widened by roughly 0.7 degrees of latitude per decade in recent years, or more than two degrees of latitude since 1979.

The tropics are hot and wet because the sun warms the air more near the equator thanks to a more direct shine. This warmed air rises and then cools, condensing its water vapor, which falls as rain. This zone of heat and wetness has been spreading south thanks to ozone pollution but the cause of its northward spread had been mysterious. But the computer simulations suggest that it is soot (with an assist from the greenhouse gas ozone again) that is helping make the northern subtropics nearly as hot as the tropics themselves.

Only by adding the warming from soot to these computer models did the results begin to mimic what is actually happening, including increased dryness in the subtropics. At present, air raised by the sun’s heat in the tropics often sinks back down as hot dry air at roughly 30 degrees latitude, creating a global belt of deserts. That belt is also beginning to move, along with the jet stream and its attendant storms.

The extra soot and ozone driving this shift in the north is coming from the increase in fossil fuel burning in the northern hemisphere. Eliminating that pollution would not only slow this tropical shift, it would also curb climate change and improve human health—and reducing fossil fuel burning can be accomplished by such simple steps as using cleaner cookstoves or improved internal combustion engines. After all, the soot that doesn’t make it to the atmosphere, often finds a final resting place in human lungs.

Image: Courtesy of Wikimedia Commons

About the Author: David Biello is the associate editor for environment and energy at Scientific American. Follow on Twitter @dbiello.

The views expressed are those of the author and are not necessarily those of Scientific American.





Rights & Permissions

Comments 12 Comments

Add Comment
  1. 1. Carlyle 4:53 pm 05/16/2012

    Another simple step would be to ban bio fuel previously promoted by environmentalists. Slash & burn farming to grow palm oil leaves a massive smoke cloud over the tropics.
    If environmentalists were genuine, they would be promoting nuclear energy.

    Link to this
  2. 2. Owl905 5:37 pm 05/16/2012

    Environmentalists weren’t the driving force in bio-fuels. Economic security in the form of dependence on imported oil was the driving force in bio-fuels. Then President Bush was targeting a 15% reduction in oil imports.

    Link to this
  3. 3. geojellyroll 6:32 pm 05/16/2012

    “The tropics—the belt of land around the equator characterized by abundant rainfall and torrid temperatures ‘

    Actually no. One needs to look at many variables…altitude, prevailing winds,currents, closeness to the ocean, etc. SOME of it has ‘torrid’ temperatures and SOME of it has abundant rainfall.

    Link to this
  4. 4. Carlyle 8:43 pm 05/16/2012

    Owl905 5:37 pm 05/16/2012
    Environmentalists were touting the benefits of bio fuel long before President G W Bush became President. The Brazilian ethanol production was repeatedly extolled. Bush believed the environmentalists. That was a mistake.

    Link to this
  5. 5. jtdwyer 10:23 pm 05/16/2012

    The article states:
    “The tropics are hot and wet because the sun warms the air more near the equator thanks to a more direct shine. This warmed air rises and then cools, condensing its water vapor, which falls as rain. This zone of heat and wetness has been spreading south thanks to ozone pollution but the cause of its northward spread had been mysterious.”

    However, isn’t the tropical air humid because the Sun’s radiation heated the tropical waters, causing it to evaporate into the air? Perhaps I’m mistaken, but without similarly (increased) warming of semitropical waters (like the Gulf of Mexico), I’m skeptical that tropical rain forests will be generally migrating Northward.

    It may more likely just get hotter and drier up here, especially in the Southwestern deserts…

    Link to this
  6. 6. alan6302 9:31 am 05/17/2012

    The internal combustion engine produces nanoparticles . These ,in turn, will interact with DNA and a CME producing death from heart disease.

    Link to this
  7. 7. Eric Zhang 10:09 am 05/17/2012

    Now, it is time for the whole world to coorperate to take measures to prevent the tendency of world warming. There is no difference between developed and developing countries, and each country has the responsibility to protect our planet-maybe the only one that is fit for the living of humans. Cutting down the emission of carbon dioxide, creating new kinds of environmental energy, and establishing a machanism to monitor the conditions of the environment are all useful means to achieve this goal.

    Link to this
  8. 8. jtdwyer 1:40 pm 05/17/2012

    Eric Zhang – Well put. Certainly the 7 billion people of Earth aren’t going any ‘New World’. One of the most critical factor contributing to the diminishment of limited natural resources and increased environmental impact of all kinds is the past and continued growth of the human population. The population has increased more than 7 fold since the beginning of the industrial revolution, and is projected to increase by nearly a third, to more than 9 billion, by 2050. Some solution must be successfully implemented.

    Link to this
  9. 9. ErnestPayne 8:25 pm 05/17/2012

    I am guessing that the tropics are also expanding, as well, to the south. The increased moisture and temperature should, probably, make the tropics less habitable and result in population movements towards the poles. If this is the case then the republican induced wave of illegal immigration will me a mere drop in the bucket compared to coming events.

    Link to this
  10. 10. jerryd 4:28 am 05/18/2012

    Geo you are just wrong as usual. Where do you get such bad data? By far most, 90%+ is torrid hot and humid.

    JT of course the seas are hotter but it’s from the same sources of GW.

    I live in Fl and our shores and some islands are disappearing. The Everglades has lost a couple hundred sq miles of land and fresh water habitat with slat water many miles farther inland than 50 yrs ago.

    Ask any older farmer and they will tell you of the crops they can now plant and others that no longer do well because the plants, birds, animals have moved north 2-300 miles.

    Just look at the pine beetle destruction that used to be killed off by low temps has move 500 miles north.

    As the 20-200′ thick peat Canadian, siberian Tundra melts and gives up it’s CO2 and methane we won’t have to worry about heating anymore.

    Link to this
  11. 11. Carlyle 9:36 am 05/19/2012

    Well I am an old farmer & bee keeper. I have seen it all before. Globally the weather in much of the world today is very similar to the early 1940s

    Link to this
  12. 12. Carlyle 10:03 am 05/19/2012

    http://takeson.blogspot.com.au/2012/04/blog-post_12.html#!/2012/04/blog-post_12.html
    Weather conditions similar to 2012 occurred in the winter of 1942, when the U.S. Midwest was unusually warm, and when the Wehrmacht encountered the formidable forces of ‘General Frost’ in a Russian winter not unlike the one Russians just had.

    Link to this

Add a Comment
You must sign in or register as a ScientificAmerican.com member to submit a comment.

More from Scientific American

Scientific American MIND iPad

Give a Gift & Get a Gift - Free!

Give a 1 year subscription as low as $14.99

Subscribe Now >>

X

Email this Article

X