A newly-published meta-analysis looks at whether science can realistically finish cataloging all the world's biological species before they go extinct:
"Some people despair that most species will go extinct before they are discovered. However, such worries result from overestimates of how many species may exist, beliefs that the expertise to describe species is decreasing, and alarmist estimates of extinction rates. We argue that the number of species on Earth today is 5 ± 3 million, of which 1.5 million are named. New databases show that there are more taxonomists describing species than ever before, and their number is increasing faster than the rate of species description. Conservation efforts and species survival in secondary habitats are at least delaying extinctions. Extinction rates are, however, poorly quantified, ranging from 0.01 to 1% (at most 5%) per decade. We propose practical actions to improve taxonomic productivity and associated understanding and conservation of biodiversity."They found that it's not true that taxonomists are a dying breed, but that the profession is undergoing a geographical shift from Western countries where modern taxonomy and big museum collections were first developed, to South America and Asia-Pacific countries. They argue that this is a good development because those are the countries where much of the world's biodiversity actually lies.
The number of active taxonomists was estimated by looking at databases to find out who is publishing new species descriptions. It's also not true that the current generation of taxonomists are mostly "one-hit wonders" who only describe one or two new species in their careers; there is not much difference between the previous and current generations of taxonomists in their productivity.
If we want to catalog all the world's biodiversity, declining lack of expertise is then not the problem. What's problematic is that even as we are still in a state of ignorance about the world's biodiversity, species are going extinct at a steady rate due to human activity. We are also victims of our own success: as more and more species have been described, it becomes harder to find new ones among the existing known diversity. It's like being stuck at home for the weekend: after you've read most of the books and watched most of the movies in your house, it's harder to find something new to do (at least before the Internet...).
But what's the point of all this taxonomic toil? Why describe new species? The questions of "how many species on Earth?" and "what is the extinction rate?" are notoriously difficult to answer. Whereas we now have a fair guess at the answer to the first question, estimates of the extinction rate vary widely, reflecting the huge uncertainties involved. As the authors point out: "Taxonomists are not in danger of extinction. They are increasing in numbers and will become more in demand as more species mean more diagnostic challenges to discriminate species, whether they are pests, pathogens, food, ecological keystone, or endangered species." This highlights how knowledge of biodiversity is important, both for its own sake and for the sake of human interests.