The manmade changes pushing the planet toward a critical
transition Nature changes gradually—until it doesn’t. As the
changes in an ecosystem pile up, they can push the system past a
“critical threshold,” and then the change can become extremely
fast (in relation to geological timescales) and unstoppable. And
in a review in the journal Nature, researchers suggest that the
same thing is happening to the whole world: Humans could be
driving Earth’s biosphere towards a tipping point beyond which
the planet’s ecosystems will collapse abruptly and irreversibly.
This global ecosystem collapse has occurred before, most
recently about 12,000 years ago with the last transition from a
glacial period to the current interglacial (i.e., warm) period,
say the review authors. Over the relatively short period of
1,000 years, fluctuations in the Earth’s climate largely killed
off about half the large mammal species, along with birds,
reptiles, and a few smaller mammal species. The millennium-long
shift was triggered by rapid