|How many documented extinctions per year ? (chapter 23)|
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To list of six examples
Summary. As a general
rule, the official IUCN criterion for confirming extinction is
for the species concerned not to be found for a period of 50
consecutive years. Lomborg downplays the rate of documented
extinctions per decade by -
a) not mentioning that the confirmation period is as long as 50 years;
b) omitting any mention of the fact that many species may have gone extinct less than 50 years ago and therefore are not yet counted as confirmed extinctions;
c) presenting the average rate of extinctions per decade over the last 400 years as being the current rate, even though he knows that the rate is much higher now than 400 years ago; and
d) using extinction data that refer to limited geographical areas or limited time spans as if they covered the whole globe for the whole period considered.
In his chapter on biodiversity,
Lomborg claims that the number of species that are going extinct
has been wildly exaggerated by the environmentalists. He claims
that "actual extinctions remain low". The number of
actual, documented extinctions is presented in his table 6 on p.
250, which, allegedly gives us "total extinctions since
1600". The data here are from IUCN, the International Union
for the Conservation of Nature, which produces the official,
international red lists. The red lists include the category
"Ex", i.e. "extinct", and by going through
the lists, you can count how many species have actually
disappeared up to the present time.
On p. 252, Lomborg remembers to mention that ". . in order to document extinction, one must have looked for the species for several years wherever it may exist." But the reader will hardly guess that "several years" means 50 years. So, in most cases, it is not yet possible to declare a species extinct if it has disappeared less than 50 years ago, i.e. later than 1950, if the status is made in the year 2000. Only if a species is particularly well known and studied - e.g. in the case of large mammals - is the 50 year rule not applied.
Thus, in many cases, the extinctions in table 6 are for the period up to 1950, not to the present day as Lomborg claims. Extinctions to the present day are recorded for mammals, birds, some fish, and many plants, but not e.g. for amphibians.
There are several other problems with the table. The data on fish are mainly restricted to North America and lake Victoria in Africa, whereas e.g. extinct fish in Asia are not included. The data on molluscs go back only to the mid 1800s, not to 1600 as indicated. The data on crustaceans and insects are practically all from North America and Hawaii, and thus do not represent the global situation. All these reservations were indicated in Lomborg´s sources, but he has forgotten to mention them here. Altogether, this means that the data for reptiles, amphibians, fish, molluscs, crustaceans and insects cannot be used in the way that Lomborg uses them.
As to the vascular plants, the table only gives extinctions up to c. 1947. There are also data for the period 1947-1997. During this latest 50 year period, 371 plant species are believed to have gone extinct, i.e. about the same number as the 396 species that disappared during the preceding 350 years. This illustrates that the extinction process is very much accelerating.
On p. 251 Lomborg writes: "Table 6 shows that about 25 species have become extinct every decade since 1600". As will be understood, this calculation is misleading: in most groups, the table does not cover 400 years, and/or it does not include the global figures. Furthermore, as the extinction rate is accelerating, it is misleading to calculate the average rate since 1600. Rather, we should try to calculate the rate during the last 50 years for those groups where this is possible. 38 species of mammals, 13 species of birds and 371 species of plants have disappeared during this period, which adds up to 422 species for these three groups combined, or 84 species per decade (Compare this with the 25 species per decade indicated by Lomborg, for all groups combined).
And of course, these reported extinctions are only a fraction of those that have actually occurred. Thus, a recent global assessment of the status of all amphibians (see www.globalamphibians.org) tells that the number of species extinct by now is at least 34 and probably as high as 147. That is, the true number of extinctions is much higher than the 5 extinctions mentioned by Lomborg.