JANUARY 13TH 2004
You may be interested in the following
comment by Bob Ferguson, on the latest scare story from the greenhouse
(Washington DC) -- Much
has been made of a paper published on January 8 in
Nature by Chris Thomas and 18 co-authors. claiming that global warming
cause a massive extinction of the earth's biota. Thomas told the Washington
Post "we're talking about 1.25 million species. It's a massive number."
Thomas et al. performed an interesting exercise in modeling. They used
accepted logarithmic relationship between the area of an ecosystem and
number of species within. Using this function as a starting point, the
researchers examined the current distributional area of 1,103 plant and
animal species from different parts of the earth, and related that to
temperature, rainfall, and seasonality. Then, using the output from various
climate models runs under scenarios that produced low, mid, and high ranges
of future global temperature change, they calculated the area of the regions
that were defined by the same climate values as the current species
As an example, if a particular bird species in Europe is currently found
a region that gets no hotter than 35ºC in the summer and no colder
in the winter, it is assumed that these same climate definitions will
the species range in the future. If the range defined by those climatic
conditions becomes smaller under projected future climate conditions,
species comes under pressure of extinction, if it stays the same or expands,
the species is categorized as not facing increased extinction pressure.
is clear to see that this methodology can only lead to a reduced number
species (i.e. a growing number of extinctions). In other words, climate
change is the sole driver of biodiversity in this calculation.
This assumption is not correct. Consider the effects on an ecosystem of
mutation of some previously harmless bacterium, a clearly non-climatic
of extinction. But placing the entire onus for extinction on climate also
calls the entire result into question.
Thomas et al. calculate percentage species extinctions for a variety of
future climate scenarios. One, with a lower limit of 0.8ºC of warming
next 50 years, produces an extinction of roughly 20% of the sampled species.
This results in a convenient Reality Check. Surface temperatures indeed
raised this amount in the last 100 years. But there is absolutely NO
evidence for massive climate-related extinctions. (One would think the
reviewers of this manuscript would have picked that up!).
There are several other major problems:
1. Global climate models, in general, predict a warmer surface and an
increased rate of rainfall. In general, as long as there is adequate
moisture, the most diverse ecosystems on earth are in the warmest regions,
the tropical rainforest being the prime example. Consequently, the general
character of future climate is one which is more, not less hospitable
2. Temperatures have been bouncing up and down a lot more than 0.8ºC
last several hundred thousand years. But Thomas' methodology implies that
there are large extinctions for each and every increment of equivalent
change, whether the temperature goes up or down. It is quite clear that
era from 4,000 to 7,000 years ago was 1-2ºC warmer than today, for
and the rapid climate changes that took place before then, at the end
last major glacial era, were multiple in nature, both up and down. Prior
then, there was the dramatic change known as the glaciation itself, when
covered much of North America. Applying this method to all those changes
should extinct just about every species on earth!
3. Species often thrive well outside their gross climatic "envelope".
U.S. Department of Agriculture has mapped the distribution of all major
species North America. For almost every species, there are separate
"disjunct" populations far away from the main climatic distribution. A
example is the Balsam fir, Abies balsamea, whose main distribution is
Canada. But there is a tiny forest of the same remaining in eastern Iowa,
hundreds of miles south (and about ten degrees warmer) than the climatic
"envelope" that Thomas et al. assume circumscribes the species. These
disjuncts are the rule, not the exception, and are one reason why the
diverse ecosystem on earth-the tropical rainforest-managed to survive
The "disjuncts" exist because climate is simply not as uniform as it is
calculated to be by gross climate models. Variations in topography and
landform create cul-de-sacs where species survive and thrive far away
their climate envelopes. It is more logical to assume a fractionating
climate will produce more disjuncts, not less.
4. Thomas et al. make what the famed agronomist Paul Waggoner has called
"dumb people" assumption: that in the face of a massive extinction there
will be no human adaptation or mitigation of the prospect. In fact we
been preserving diversity artificially, in the form of parks and zoos,
In addition, the amount of "artificial" genetic diversity is rising
dramatically with the technology of modern genetics. It is difficult to
imagine, decades from now, that these technologies will not be applied
ameliorate some prospective massive extinction.
Obviously, there is a lot to criticize in this paper. What is surprising
that something with such inconsistencies and unrealistic assumptions made
unscathed through the review process in such a prestigious journal as
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