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Global Warming & Hurricane Intensity

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  • CraigGingold
    http://www.csmonitor.com/2005/0801/p03s01-sten.html Christian Science Monitor August 01, 2005 As planet warms, storms grow stronger Scientists see evidence
    Message 1 of 1 , Aug 1, 2005

      Christian Science Monitor

      August 01, 2005

      As planet warms, storms grow stronger

      Scientists see evidence that hurricanes and typhoons have
      intensified. Are new responses needed?

      By Peter N. Spotts | Staff writer of The Christian Science Monitor

      For years, hurricanes and typhoons have served as poster children for
      the hazards of global warming.

      When simulated tropical storms churn inside the silicon universe of
      researchers' computers, such cyclones grow in power, and sometimes in
      number as well, as tropical temperatures increase. But when researchers
      have looked for global warming's fingerprints on real tropical cyclones,
      the evidence often has been inconclusive.

      Now, one of the top researchers in the field reports that worldwide, these
      storms are nearly twice as powerful today as they were 30 years ago.
      Global warming has intensified the trend, exerting an influence stronger
      than he would have believed even a few months ago, he says.

      "I'd been thinking of a very modest response" of tropical cyclones to
      climate change, "and what we're seeing is not so modest," says Kerry
      Emanuel, a professor of atmospheric science at the Massachusetts
      Institute of Technology in Cambridge, Mass.

      The upshot: The 21st century could be a rough one for people who settle
      in hurricane or typhoon-prone areas.

      As a result, more communities should be drawing on the experience of
      states such as Florida in devising building and zoning codes that can
      reduce damage and fatalities, analysts say. For people who insist on
      building on vulnerable barrier islands or along fragile coasts, insurance
      companies should be given a freer hand in deciding who they will cover
      and what they will charge for hurricane insurance, researchers and policy
      analysts say.

      Strong start to hurricane season

      Dr. Emanuel's results are appearing at a time when residents along the
      US Gulf Coast and throughout the Caribbean are still recovering from what
      forecasters are calling the most active start to the hurricane season on
      record. Since June 1, six storms grew strong enough to merit names --
      from Arlene to Cindy to Franklin. Three became hurricanes. Two reached
      a potent category four out of five. According to forecasters at the National
      Hurricane Center in Miami, hurricane Dennis, which reached category four
      on July 7, ranks as the earliest Caribbean storm on record to reach that

      Some researchers argue that in practical terms, the allure to live near the
      sea will do far more to boost society's risk from such storms over the next
      several decades than any effect global warming could have on the storms

      Until he concluded this study, Emanuel says he was among that group.
      Now, he says, global warming's impact on the storms may play a bigger
      role than previously believed in putting societies at risk, particularly in
      less-developed countries. Dr. Emanuel's research, published Sunday on
      the journal Nature's website, adds a fresh perspective to the discussion
      about the effects of global warming on tropical cyclones, says Kevin
      Trenberth, a senior scientist at the National Center for Atmospheric
      Research in Boulder, Colo.

      Early on, concerns about the future of these storms arose based on
      computer forecasts and basic theory. "Given the information we had at the
      time, the results were overhyped a bit," Dr. Trenberth acknowledges. He
      notes that the study doesn't have much comment on the effects of storm
      surges and torrential rainfall that accompany land-falling hurricanes --
      factors far more destructive than winds.

      Still, Emanuel's approach "adds a new element," says Trenberth. It shows
      a strong real-world correlation between the oceans' current warming
      trend - which scientists have linked to the heating- trapping effect of
      industrial carbon dioxide and other "greenhouse gases" - and the
      increasing power of tropical cyclones.

      Global warming vs. natural cycle

      Other researchers have noted that this is more likely a natural period
      of intense activity for Atlantic hurricanes. For example, William Gray,
      a specialist in tropical meteorology at Colorado State University who
      pioneered seasonal hurricane forecasts, notes that the region goes
      through swings in activity that can span decades. He and his colleagues
      have noted that the US and its southern neighbors have faced above-
      average hurricane seasons for the past decade and is likely to do so for
      some time to come.

      Emanuel acknowledges that such cycles are important. Depending on the
      region under scrutiny, the impact of natural cycles such as El NiƱo, or the
      multidecade cycles Dr. Gray observes, can swamp any global-warming
      signal the storms may carry. But viewed worldwide, the signal starts to

      His latest finding, he says, grew out of attempts to answer a broader
      question: Do hurricanes help drive large-scale ocean currents? These
      currents carry tropical waters toward the poles, bringing warmth to middle
      and high latitudes.

      Measuring a typhoon's punch

      Initial calculations suggested that hurricane activity could account for
      up to half or more of the driving force behind these currents. If so, a
      significant long-term rise in tropical cyclones could push warmer water
      toward higher latitudes. This could lead to warmer average temperatures
      at middle and high latitudes than climate models currently project.

      To answer the question, however, Emanuel needed to gauge a hurricane's
      or typhoon's punch. So he built a measure based on sustained wind
      speeds over the life of each storm and on each storm's duration.
      Combined they reflect a storm's total power output. Since the mid-70s,
      storm power fluctuated with well-known natural cycles. But through this
      natural "noise," global warming's signal emerged as an increase in
      strength that tracked rising temperatures in the tropical oceans' surface

      The work certainly will not be the last word on the subject. Some
      researchers are already raising questions about Emanuel's approach.

      In one sense, however, there is broad agreement, notes Roger Pielky Jr.,
      director of the Center for Science and Technology Policy Research at
      the University of Colorado at Boulder. Whether scientists attribute the
      increased tropical cyclone intensity to global warming or natural cycles,
      the trend is likely to hold for at least a decade.

      Looking at the costs to society from these storms, for every dollar in
      damage from tropical cyclones the Intergovernmental Panel on Climate
      Change anticipates by 2050, the IPCC's demographic numbers suggest
      that societal changes will add another $22 to $60 in impact. "If you're a
      planner, you're saying: We'd better get ready," Dr. Pielke observes.
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