| Details1: | CLIMATE CHANGE AND BIODIVERSITY LOSS
Report in Nature 427, 145-148 (8 Jan. 2004);
by C.D. Thomas et al
http://www.nature.com/nature/links/040108/040108-1.html
Many plant and animal species are unlikely to survive climate change. New
analyses suggest that 15-37% of a sample of 1,103 land plants and animals
would eventually become extinct as a result of climate changes expected by
2050. For some of these species there will no longer be anywhere suitable
to live. Others will be unable to reach places where the climate is
suitable. A rapid shift to technologies that do not produce greenhouse
gases, combined with carbon sequestration, could save 15-20% of species
from extinction. The cover shows a species in the firing line. Boyd's
forest dragon, Hypsilurus boydii, is found in Queensland, Australia. About
90% of its distribution would become climatically unsuitable by 2050, on
maximum climate warming scenarios.
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EXTINCTION RISK FROM CLIMATE CHANGE?
Critique by Robert Ferguson,
Center for Science and Public Policy
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 will 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 an
accepted logarithmic relationship between the area of an ecosystem and the
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
distribution.
As an example, if a particular bird species in Europe is currently found in
a region that gets no hotter than 35ºC in the summer and no colder than 0ºC
in the winter, it is assumed that these same climate definitions will bound
the species range in the future. If the range defined by those climatic
conditions becomes smaller under projected future climate conditions, the
species comes under pressure of extinction, if it stays the same or
expands, the species is categorized as not facing increased extinction
pressure. It is clear to see that this methodology can only lead to a
reduced number of 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 the
mutation of some previously harmless bacterium, a clearly non-climatic
cause 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 in
the next 50 years, produces an extinction of roughly 20% of the sampled
species.
This results in a convenient Reality Check. Surface temperatures indeed
have 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 for
biodiversity.
2. Temperatures have been bouncing up and down a lot more than 0.8ºC in the
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 the
era from 4,000 to 7,000 years ago was 1-2ºC warmer than today, for example,
and the rapid climate changes that took place before then, at the end of
the last major glacial era, were multiple in nature, both up and down.
Prior to then, there was the dramatic change known as the glaciation
itself, when ice 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". The
U.S. Department of Agriculture has mapped the distribution of all major
tree species North America. For almost every species, there are separate
"disjunct" populations far away from the main climatic distribution. A fine
example is the Balsam fir, Abies balsamea, whose main distribution is
across 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
most diverse ecosystem on earth-the tropical rainforest-managed to survive
the ice age.
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 from
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
the "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
have been preserving diversity artificially, in the form of parks and zoos,
for centuries.
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 to
ameliorate some prospective massive extinction.
Obviously, there is a lot to criticize in this paper. What is surprising is
that something with such inconsistencies and unrealistic assumptions made
it unscathed through the review process in such a prestigious journal as
Nature.
Quelle: NEWSLETTER v. 24.01.2004
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