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scientists in 2003 would have guessed. If they thought that business as
usual might trigger irreversible global warming around 2030, twenty-
seven years later, the reckless emission of greenhouse gases over the last
ten years has undoubtedly moved up the date much closer to the present.
These physical facts alone are dire. We have over twice the reductions
to achieve as we did only a few years ago and far less time in which to
achieve them. Very soon, the present in which we live and the future in
which we would cross the tipping point will coincide—and we'll dis-
cover we've already passed the point at which those positive feedback
loops kick in.
Doing some arithmetic based on these facts may help clarify our situa-
tion. In 2003 it once seemed we'd meet our goals by 2030, but we've man-
aged to waste ten years or so. If we once needed to achieve seven wedges,
we now need to achieve eighteen— plus a further increment to hit a target
not of 500 ppm, but of 350. Since we are already above the equivalent
of 450 ppm, if we wish not to go too far beyond that level we will have
to try to eliminate fossil-fuel use entirely, and thus to achieve twenty-five
wedges, as Hoffert suggests. But to do so now, after several years since his
study have gone by, we'd most likely need to hit around thirty wedges. Yet
we'd need to add a further increment to take into account the fact that the
biosphere will absorb less of what we emit in the coming years. A back-
of-the envelope calculation suggests that if we acted today we would need
to reduce our emissions by at least thirty-two wedges. Moreover, thanks
to our profligacy in recent years, as well as our sense that we must hit a
lower target, it's also likely we would need to achieve these cuts many
years earlier.
Other ways of estimating the challenge confirm these figures. At the
Copenhagen summit on climate change in 2010, a majority of nations
endorsed a target of raising the Earth's temperatures no more than 1.5°
Centigrade above preindustrial levels. But since we've already raised the
average temperature by 0.8°, and the temperature will rise another 0.6°
due to the inertia of the world's climate, 1.4 of those 1.5° are already inev-
itable, leaving us virtually without hope of reaching the target. 77 Even if
we acted today to eliminate our greenhouse gas emissions entirely , we'd
still barely meet our goal. And there is simply no chance we can eliminate
all those emissions so quickly.
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