Trade winds and food chain – Pacific – 05/10/2006

  • November 23, 2013 at 11:47 pm #1207

    rocky and ginnicus wrote:
    Global warming weakens Pacific trade winds
    Long-term effect could disrupt marine food chain
    This illustration show how the loop of circulating wind over the
    Pacific Ocean known as the Walker circulation works.
    View related photos
    Gabriel Vecchi / UCAR

    Updated: 1:45 p.m. ET May 3, 2006
    NEW YORK – The trade winds in the Pacific Ocean are weakening as a
    result of global warming, according to a new study that indicates
    changes to the region’s biology are possible.

    Using a combination of real-world observations and computer modeling,
    researchers conclude that a vast loop of circulating wind over the
    Pacific Ocean, known as the Walker circulation, has weakened by about
    3.5 percent since the mid-1800s. The trade winds are the portion of
    the Walker circulation that blow across the ocean surface.

    The researchers predict another 10 percent decrease by the end of the
    21st century.

    The effect, attributed at least in part to human-induced climate
    change, could disrupt food chains and reduce the biological
    productivity of the Pacific Ocean, scientists said.

    The study was led by Gabriel Vecchi of the University Corporation for
    Atmospheric Research and is detailed in the May 4 issue of the
    journal Nature.

    The researchers used records of sea-level atmospheric pressure
    readings from as far back as the mid-1800s to reconstruct the wind
    intensity of the Walker circulation over the past 150 years. A
    computer climate model replicated the effect seen in the historical

    Some of the computer simulations included the effects of human
    greenhouse gas emissions; others included only natural factors known
    to affect climate such as volcanic eruptions and solar variations.

    “We were able to ask ‘What if humans hadn’t done anything? Or what if
    volcanoes erupted? Or if the sun hadn’t varied?'” Vecchi said. “Our
    only way to account for the observed changes is through the impact of
    human activity, and principally from greenhouse gases from fossil
    fuel burning.”

    Earth’s average temperature has risen by about 1 degree Fahrenheit
    over the past century and many scientists believe greenhouse gases
    and carbon dioxide emissions from human activities are to blame.

    “This is evidence supporting global warming and also evidence of our
    ability to make reasonable predictions of at least the large scale
    changes that we should expect from global warming,” Vecchi told

    By extrapolating their data and combining it with results from other
    models, the researchers predict the Walker circulation could slow by
    an additional 10 percent by 2100.

    Driving force

    The trade winds blow from the east at an angle towards the equator
    and have been used by sailors for centuries seeking to sail west.
    Christopher Columbus relied on the Atlantic’s trade winds to carry
    him to North America. The winds get their name from their
    reliability: To say that a “wind blows trade” is to say that it blows
    on track.

    The overall Walker circulation is powered by warm, rising air in the
    west Pacific Ocean and sinking cool air in the eastern Pacific.

    This looping conveyer belt of winds has far-reaching effects on
    climate around the globe. It steers ocean currents and nourishes
    marine life across the equatorial Pacific and off the coast of South
    America by driving the upwelling of nutrient-rich cold water from
    ocean depths to the surface.

    The Walker circulation is also primarily responsible for transporting
    water vapor that evaporates from the ocean surface west, towards
    Indonesia; there, the moisture rises up into the atmosphere,
    condenses, and falls back to Earth as rain.

    Several theories on the effects of global warming predict a weakening
    of the Walker circulation. Scientists think it works like this:

    To remain energetically balanced, the rate at which the atmosphere
    absorbs water vapor must be balanced by the rate of rainfall. But as
    temperatures rise and more water evaporates from the ocean, water
    vapor in the lower atmosphere increases rapidly. Because of various
    physical processes, however, the rate of rainfall does not increase
    as fast.

    Since the atmosphere is absorbing moisture faster than it can dump
    it, and because wind is the major transporter of moisture into the
    atmosphere, air circulation must slow down if the energy balance is
    to be maintained.

    A drop in winds could reduce the strength of both surface and
    subsurface ocean currents and dampen cold water upwelling at the

    “This could have important effects on ocean ecosystems,” Vecchi
    said. “The ocean currents driven by the trade winds supply vital
    nutrients to near-surface ocean ecosystems across the equatorial
    Pacific, which is a major fishing region.”

    Copyright 2006 The Associated Press. All rights reserved.

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