The Earth has never stood still.
Change is built into the life of the planet, whether physical changes to the
surface of the Earth — through the slow action of erosion or glaciation — or
biological changes to the species that populate it. We only have to go back to
the last ice age — which peaked just 20,000 years ago, a coffee break in
geological time — to see a climate that is utterly different from the one human
beings have thrived in for the last few thousand years. Heraclitus had it right:
the only constant is change.
So it's not the fact that the
global environment and the climate are changing that so worries many scientists.
It's the rate of change — and whether or not human beings, and everything else
that lives on the Earth, can adapt. Because the Earth, it turns out, is changing
very, very fast.
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This is the sobering conclusion of
a study published in the journal Nature earlier this month. Scientists from
around the world looked at past research on ecological change, and found that
the planet may be approaching a "critical transition," otherwise known as a
"tipping point," as a result of human activity like agriculture and
urbanization. The Earth has experienced tipping points before, during great
periods of mass extinctions, like the death of the dinosaurs, and most recently
when the last ice age ended around 11,000 years ago. But the idea that the Earth
could undergo such a change while we're living on it — and that it could
potentially happen in our lifetimes — is frightening. "It really will be a new
world, biologically," said Anthony Barnosky, a professor of integrative biology
at the University of California-Berkeley and a lead author on the paper. "This
could happen in just a few generations."
It's important to understand just
how much human beings have changed the planet. Human population has quadrupled
just in the past century, and today we add around 77 million people a year — an
increase that is three orders of magnitude higher than the average yearly growth
humanity experienced as recently as 400 years ago. We've converted 43% of the
Earth's land to agricultural or urban landscapes — with farms taking up most of
that space — and even the remaining territory tends to be crisscrossed by roads.
That's a larger amount than the 30% of the Earth's surface that went from being
covered by ice to being glacier-free at the end of the last ice age. We've
increased the atmospheric concentration of carbon dioxide by more than a third,
we've made the oceans more acidic and we've presided over the disappearance of
so many species that many scientists believe we're living through the sixth
great wave of extinctions All of these changes are speeding up, not slowing
down.
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So is it possible that we really
could be nearing a tipping point? No one can say for sure, and environmentalists
have been burned in the past by premature predictions that the world was on its
way to ending. But the Nature authors note that current trends suggest that half
the Earth's land surface will be disturbed by human activity by 2025 — and that
could represent the point of no return for a livable planet. "Looking into the
past tells us unequivocally that, yes, it can really happen," said Barnosky. "I
think if we want to avoid the unpleasant surprises, we want to stay away from
that 50% mark."
Unfortunately, we aren't doing a
very good job of that. Another report released last week by the U.N. Environment
Programme (UNEP) found that little progress has been made over the last five
years on 90 of the most crucial environmental goals. Significant progress has
been made on just four of those objectives. And there is little expectation that
the Rio+20 Earth Summit, which begins next week, will make much of a difference.
"This is an indictment," UNEP executive director Achim Steiner said at a news
conference in Rio de Janeiro last week. "We live in an age of irresponsibility
that is also testified and documented in this report."
Of course, in some parts of the
world — the high Himalayas of Nepal, in the desperately poor and hungry parts of
sub-Saharan Africa, in the hot and dry patches of the American southwest — a
tipping point may have already been reached and passed. The scary thing about a
tipping point is that you only know for sure that it exists once you've reached
it — and after that, it's too late to go back.
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