LL AROUND THE world, mankind is hacking enormous branches off the tree of life. Since the last ice age – which ended about 10,000 years ago – the extinction rates of plant, mammal, bird, insect, amphibian and reptile species have skyrocketed, with one estimate putting the current rate of loss at up to 140,000 species per year. That’s a problem – not just for the species that are dying out but for humans, too. We depend on our companions for food security, clean water, clothing and even the air we breathe (see p46) .
In 2009, the Stockholm Resilience Centre listed biodiversity loss as one of nine ‘planetary boundaries’ that cannot be crossed without the world suffering irreversible environmental change (other boundaries include ozone depletion, climate change and ocean acidification). Without Earth’s biodiversity, humans wouldn’t be here at all. And even the most conservative estimates of species loss show cause for alarm. The latest calculations come from a group of biologists led by Stanford University’s Paul Ehrlich and Gerardo Ceballos from the National Autonomous University of Mexico, who have published results showing that Earth is experiencing the beginnings of an extinction event at least as large as the one the killed the dinosaurs, and perhaps as big as the other four major extinctions in our planet’s history (see below). “We’re not there yet but we can easily get there in a century,” Ehrlich says.
Their paper sets out a best- case scenario – one that only counts species as going extinct if we’ve seen them go extinct, and where the ‘normal’