Geology Reference
In-Depth Information
Some animal and plant species may not fare so well. The loss of northern polar ice will
reduce the familiar habitat of polar bears, adding challenges to a population that appears to
be shrinking. A rapid shift of climate zones toward the poles may also stress many other
threatened species, notably birds, which are particularly susceptible to alterations in their
migratory nesting and feeding areas. One recent report estimated that an average global
temperatureriseofjustacoupleofdegrees,wellwithinpredictionsofsomeclimatemodels
for the next century, could trigger extinction rates among birds approaching 40 percent in
Europeandexceeding70percentinthelushrainforestsofnortheasternAustralia. Another
sobering international report found that nearly one in three of the approximately six thou-
sand known species of frogs, toads, and salamanders is similarly endangered, mainly by
the rapid warmth-driven expansion of a deadly amphibian fungal disease. Whatever else
transpiresoverthecomingcentury,itdoesappearthatweareenteringatimeofaccelerated
extinction.
Certain transformative events of the next century—some guaranteed, others highly pos-
sible—will be instantaneous: the disruption of a great earthquake, the eruption of a mega-
volcano, or the impact of a mile-wide asteroid. Human societies tend to be ill prepared for
the once-in-a-century storm or earthquake, much less for the truly catastrophic once-in-a-
thousand-years disaster.AswereadEarth'sstory,weseethattheseshockingeventsarethe
norm, inevitable, a part of the continuum of our planet's history. Nevertheless, we build
our cities on the flanks of active volcanoes and on some of Earth's most active fault zones,
hoping that in our time we will dodge the tectonic bullet (if not the cosmic missile).
Inbetweentheveryslowandveryfastarefluctuatinggeologicalprocessesthatnormally
take hundreds or thousands of years—shifts in climates, sea level, and ecosystems that are
usuallynoticeableonlyoverthespanofseveralgenerations.The
rates
ofsuchchanges,not
the changes themselves, should be our biggest concern. For climate, sea level, and ecosys-
tems can reach tipping points. Pushed too far, positive feedback loops can kick in. What
normally takes a thousand years could transpire in a decade or two.
Complacency is easy, especially when bolstered by flawed readings of the rocks. For
a while, until 2010, concerns about modern times were somewhat assuaged by ongoing
studies of a parallel scenario 56 million years ago—one of the mass extinctions that dra-
matically affected the early evolution and spread of mammals. This harsh event, called the
Paleocene-Eocene Thermal Maximum, or PETM for short, saw the relatively sudden dis-
appearance of thousands of species. The PETM is important for our time because it is the
most rapid well-documented temperature shift in Earth history. A relatively fast volcano-
induced increase in concentrations of atmospheric carbon dioxide and methane, the twin
heat-trappinggasesofthegreenhouseeffect,causedmorethanathousandyearsofpositive
feedbacks and a corresponding episode of modest global warming. Some researchers saw
the PETM as a close parallel to today's events, bad, to be sure— with an almost 10-degree
