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Re: Mystery of Mass Extinctions Is No Longer Murky
If: 1) the recent rise in global temps is caused by increased partial pressures
of greenhouse gases.
2) our current climate system is such that a "run-away" greenhouse can
3) current increased levels of greenhouse gases are driven by human
activity (very little reasonable doubt about this last).
Then: we may set the bar of mass extinction to a level impossible to exceed.
--- On Tue, 7/1/08, Michael Habib <email@example.com> wrote:
> From: Michael Habib <firstname.lastname@example.org>
> Subject: Re: Mystery of Mass Extinctions Is No Longer Murky
> To: "'DML Dinosaur Mailing List'" <email@example.com>
> Date: Tuesday, July 1, 2008, 10:53 PM
> > If we want to rank ourselves amongst mass extinction
> causes, then
> > we'll really have to lift our game. Extinction
> events caused by direct
> > or indirect human activity are nothing compared to
> those in the
> > geologic past. The Permian/Triassic extinctions in
> particular really
> > raised the bar.
> Our "ranking" as a mass extinction cause depends
> a great deal on how
> you deal with the differing temporal scales. The total
> diversity loss
> due to humans, to date, is modest compared to any of the
> extinctions of the past (especially the Permian/Triassic,
> mentioned). However, the *rate* of extinction may be
> Thus, if we assume that the current rate holds for tens of
> thousands of
> years, the total percentage loss could be comparable to at
> least some
> of the mass extinctions.
> It depends a great deal on how fast the mass extinctions of
> geologic past really were, which is hard to get a precise
> measure on.
> Some were clearly very fast, geologically speaking, but to
> comparisons to the modern rate, we need even better
> precision than is
> currently available. The comparison is also made difficult
> by the
> issues of taxon sampling. And, of course, there is the
> issue of
> extrapolation: do we make the comparison assuming that all
> species that are threatened bite the dust, or some
> fraction? Can we
> take the rate over the last 100 years and extrapolate to
> get the
> expected numbers in 1 million years, or should we expect
> the rate to
> taper after those species most susceptible to human
> mediated effects
> The upshot is that one can get numbers that are comparable
> "expected" human-mediated extinctions, and the
> estimated mass
> extinctions of the past, but only with a given set of
> Other sets (which are not objectively better or worse) give
> different numbers.
> Michael Habib, M.S.
> PhD. Candidate
> Center for Functional Anatomy and Evolution
> Johns Hopkins School of Medicine
> 1830 E. Monument Street
> Baltimore, MD 21205
> (443) 280 0181