Geology Reference
In-Depth Information
rise in global temperatures, a rapid rise in sea level, acidification of the oceans, and signi-
ficant poleward shifts in ecosystems—but not so catastrophic as to threaten the survival of
most animals and plants.
Shocking recent discoveries by Penn State geologist Lee Kump and his colleagues may
have destroyed any lingering cause for optimism. In 2008 Kump's team was given access
to a drill core from Norway that preserved the entire interval of the PETM—sedimentary
rocksthat,layerbylayer,documentedinexquisitedetailtheratesofchangeofatmospheric
carbondioxideandclimate.ThebadnewsisthatthePETM—whathasformorethanadec-
ade been thought to be the most rapid climate disruption in Earth's history—was triggered
by atmospheric changes less than a tenth the intensity of what is happening today. Global
changes in atmospheric composition and average temperature that took more than a thou-
sand years during the PETM extinction scenario have been surpassed in just the last hun-
dred years, as humans have burned immense quantities of carbon-rich fuels.
There is no known precedent for such rapid change, and no one knows how Earth will
respond. At an August 2011 meeting of three thousand geochemists in Prague, the mood
among climate specialists familiar with the new PETM data was sober. Though public pre-
dictions by these cautious experts have remained measured, the comments I heard over a
beer were pessimistic, frightening. If greenhouse gas concentrations rise too rapidly, no
known mechanisms can absorb the excess. Will warming trigger a massive methane re-
lease, with all the positive feedbacks that that scenario might entail? Will sea level quickly
rise hundreds of feet, as it has so many times in the past? We are venturing into terra in-
cognita—conducting anill-conceived global-scale experiment onEarth perhaps unlike any
that has come before.
Whatthetestimonyoftherocksdoesrevealisthat,asresilientaslifeitselfisandalways
will be, the biosphere experiences great stress at tipping points, during times of sudden cli-
mate shifts. Biological productivity, including agricultural productivity, will most certainly
fall precipitously for a time. Under such dynamic conditions, large animals like ourselves
will pay the dearest price. The coevolution of rocks and life will continue unabated, to be
sure, but humanity's role in that multibillion-year saga remains unknowable.
Have we already reached such a tipping point? Probably not in this decade, maybe not
in our lifetimes. But that's the thing about tipping points—you can never be sure you're
at one until it's happened. The housing bubble bursts. The populace of Egypt revolts. The
stock market crashes. We realize what's happening only in retrospect, when it's too late to
restore the status quo. Not that there has ever been any such thing in the story of Earth.