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An Unsettled Forecast for Global Warming
The Chronicle of Higher Education, 5.1.7



    Climate science, Doug Macdougall writes, "is notoriously difficult,
    because there are so many interconnected variables at work that cause
    and effect are often impossible to discern with confidence."
    Those variables, which Macdougall discusses in Frozen Earth: The Once
    and Future Story of Ice Ages, published recently by the University of
    California Press, have bedeviled the debate over global warming from
    the beginning.
    Complexity breeds uncertainty, and uncertainty can lead to confusion
    in the general public and to deliberate obfuscation on the part of
    those who fear that any action to stem global warming would upset the
    economic status quo or their narrow self-interest. So while
    environmental activists and many climate scientists warn that the
    status won't be quo much longer without bold steps to curb the
    emission of greenhouse gases, skeptics try to sow doubts about the
    need to respond at all.
    In that charged political climate, Macdougall, a professor of earth
    sciences at the Scripps Institution of Oceanography at the University
    of California at San Diego, offers a sober look at what we have
    learned about climate change and what we still need to learn. His book
    comes as more and more scientific studies and journalistic accounts
    document changes that already seem to be taking place. The focus of
    those reports has shifted from the global phenomenon to the impacts
    that warming may have on particular places, habitats, and lifestyles.
    In November a panel of 300 scientists from eight countries released
    the results of a comprehensive, four-year study of the impact of
    warming on the Arctic region. The Arctic Climate Impact Assessment
    concluded that the region was undergoing "some of the most rapid and
    severe climate change on earth." The assessment showed that 386,100
    square miles of sea ice -- about 8 percent of the total in the Arctic
    -- had been lost in the last 30 years and that winter temperatures in
    Alaska and western Canada had risen by from 5 to 7 degrees Fahrenheit
    since the middle of the last century.
    "These changes in the Arctic provide an early indication of the
    environmental and societal significance of global warming," the
    assessment said.
    While the changes may be most extensive in the Arctic, they appear to
    be worldwide. Glaciers are shrinking in the Himalayas, the Rockies,
    and, as Mark Lynas, a writer and activist, describes -- in High Tide:
    The Truth About Our Climate Crisis, published last summer by Picador
    -- in the Peruvian Andes.
    He reports that glaciers in Peru's Cordillera Central lost a third of
    their volume from 1970 to 1997 and "will disappear altogether in just
    a few decades unless global temperatures stop rising." That could have
    disastrous consequences for the people of Lima, Peru's capital, who
    depend on the Rímac River for their drinking water. Once the glaciers
    are gone, he says, the Rímac, "which through the late twentieth
    century has been temporarily charged with additional meltwater from
    the rapidly retreating ice fields, will suddenly -- and disastrously
    -- dry up for half the year."
    "It's difficult to imagine quite how a massive Third World city might
    cope with a crisis on this scale," Lynas writes. "With no water supply
    for six months every year, life will quickly become impossible. Where
    will the residents go? There is no spare land in the mountains, and
    few could survive in the jungle. Whilst the rich could pay for fresh
    water to be trucked in, the poor -- the massive majority of Lima's
    population, who already have difficulty accessing reliable water
    supplies -- will be forced to move or die."
    Last summer the BBC reported on the findings of Scottish scientists
    who found that on the Shetland and Orkney Islands hundreds of
    thousands of seabirds had failed to breed this year. The most likely
    cause, they said, was rising seawater temperatures that had led to the
    disappearance from waters around the islands of the sand eel, a small
    fish that has been a key part of the food chain for the seabirds. The
    scientists speculated that the plankton on which the sand-eel larvae
    feed are moving northward to avoid the warmer seawater temperatures.
    In October two environmental groups Results for America and Clean
    Air-Cool Planet -- held a briefing for reporters in which they warned,
    "Global warming already is starting to change New England's climate,
    endangering fall colors from hardwood forest maples and other trees.
    Over the next 100 years, the emerging climate-change trend could wipe
    out all or most of the autumnal foliage for which the region is best
    known and upon which its tourism economy is heavily dependent."
    At the briefing, Barrett N. Rock, a professor of natural resources at
    the University of New Hampshire, reported, "Just 40 or 50 years ago,
    New England and New York produced about 80 percent of the world's
    maple syrup, compared to 20 percent in Canada. Now the ratio has been
    reversed as the optimal maple-sugar growing and tapping conditions
    have shifted north."
    At another briefing in October, held at the Center for Health and the
    Global Environment at the Harvard Medical School, James J. McCarthy, a
    biological oceanographer at Harvard University, said that "global
    warming may well be causing bigger and more powerful hurricanes.
    Warmer seas fuel the large storms forming over the Atlantic and
    Pacific, and greater evaporation generates heavy downpours." McCarthy,
    the lead author of one section of the Intergovernmental Panel on
    Climate Change's Third Assessment Report, issued in 2001, added, "With
    warmer, saltier tropical seas, the IPCC has projected larger storms,
    heavier rainfalls, and higher peak winds."
    And a study conducted by 19 scientists of the effects of climate
    change on California found that warming could, among other things,
    have a devastating impact on the state's wineries because it would
    lead to poorer-quality grapes. The study, which was published in the
    online version of the Proceedings of the National Academy of Sciences
    in August, also indicated that the snow pack in the Sierra Nevada
    could be reduced by 70 to 90 percent.
    Complicating the debate further, some computer models show that there
    will be winners and losers as global warming continues, and that -- at
    least in the short term -- the winners will be in the developed world.
    A study of the impacts of warming on agriculture by two scientists at
    Yale University's School of Forestry and Environmental Studies
    suggests that climate change will economically benefit countries in
    temperate areas but damage crops in countries closer to the Equator.
    "The 'winners,' ironically, are the developed countries that have done
    the most to produce these warming trends," says Robert Mendelsohn, a
    professor of forest policy who led the study.
    For many scientists and environmentalists, such evidence amounts to a
    compelling case that human-induced warming is producing or will
    produce significant disruptions in our way of life. Even so, as
    Macdougall points out in Frozen Earth, we still don't understand
    exactly what is going on. "There is no such thing as average weather,"
    he notes. "Weather is what we experience daily, and it can be
    misleading, because we are impressed most by the extremes."
    To try to understand how the climate, as opposed to the weather, is
    changing, he looks at large changes on a longer time scale than the
    last few decades, pointing out that we are still in an ice age that
    reached its peak 20,000 years ago. At the moment, he says, we "are in
    the midst of the maximum warmth of an interglacial period." More
    important, he notes, "A hallmark of Ice Age climate change, at least
    when viewed from the perspective of its impact on human societies, is
    abruptness. With little or no warning, there have been drastic shifts
    in temperature, storminess, and precipitation, both regionally and
    Rapid climate shifts seem to take place when a threshold has been
    crossed, he adds, and some external process has to trigger that
    crossing. Recently, computer simulations have suggested that a change
    in ocean circulation may be one such trigger.
    "In particular," Macdougall writes, "changes in the way ocean
    circulation occurs in the North Atlantic Ocean have been implicated in
    some of the large and abrupt temperature changes observed in the
    Greenland ice-core data over the past few tens of thousands of years."
    He points to evidence from the distant past that large infusions of
    fresh water into the North Atlantic have affected ocean circulation
    and brought on prolonged cold periods in the Northern Hemisphere. If
    today's warming continues, melting glaciers in the Arctic could
    provide such an infusion. That prospect has caused some scientists to
    predict that global warming could lead to something akin to the
    "Little Ice Age," the period from the 14th to the 19th centuries when
    Europe and North America experienced extended periods of unusual cold.
    While the mechanisms that lead to abrupt climate change remain
    mysterious, he says, we have "several good examples of past
    civilizations collapsing as a result" of it -- from the Akkadians
    4,200 years ago in Mesopotamia to the Maya 1,100 years ago in Central
    "Modern societies," he adds, "for the most part are better equipped to
    deal with such surprises than were those of even a hundred years ago,
    but are not entirely immune. Just-in-time logistics systems and highly
    concentrated and specialized agriculture are as likely to be disrupted
    by abrupt climate change as some earlier technologies." Even now, he
    says, energy grids have trouble dealing with heat waves and cold
    So, while Macdougall warns against reading too much into short-term
    changes in the weather, his analysis of the long term remains
    unsettling. We cannot predict, "even in a general way," he says, "what
    may happen to the climate system as a result of human influences. A
    great, unintended experiment in 'climate forcing' is under way as we
    add more and more greenhouse gases to the atmosphere. Whether or not
    we shall reach one of those thresholds that seem to separate different
    climate modes, and what will happen if we do, is still unknown."

    Malcolm G. Scully is The Chronicle's editor at large.

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