Twenty years ago, the Earth Summit in Rio resulted in a Convention on Biological Diversity, now signed by 193 nations, to prevent species loss. But can we tell how many species are becoming extinct?
One statement on the Convention's website claims: "We are indeed experiencing the greatest wave of extinction since the disappearance of the dinosaurs."While that may (or may not) be true, the next sentence is spuriously precise: "Every hour three species disappear. Every day up to 150 species are lost."
Even putting aside the apparent mathematical error in that claim (on the face of it, if three species are disappearing every hour, 72 would be lost every day) there is an obvious problem in generating any such number. No-one knows how many species exist. And if we don't know a species exists, we won't miss it when it's gone.
