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rethink how our ecosystems and economies will survive, and find a “new
normal” in which to live. But this implication is simply too optimistic.
Unless we make severe, thorough, and uncompromising changes soon,
temperatures will climb to a high level. The longer they remain at that
level, as they will, the more likely they are to trigger positive feedback
loops—and thus create a further round of warming, with a further series
of harsh consequences for the climate. These possibilities were not incor-
porated into the projections of climate change provided in the IPCC
report in 2007, nor were they a factor in the scenarios of adaptation
sketched there. The reality we face, then, is somewhat tougher than we
thought a few years ago. The most likely scenario we face is that changes
to Earth's climate systems will accelerate and get steadily worse , step by
lurching step, for decades—as various feedback loops kick in and impose
devastating effects. The release of methane gas from the permafrost in the
far North, for example, if it takes effect on a large scale, will lead to a rapid
round of global warming, which in turn could trigger a wholesale col-
lapse of the Amazonian ecosystem, with all its consequences for weather
in the Americas, and a general increase in carbon concentrations in the
atmosphere, which could in turn trigger feedback loops elsewhere. Once
we pass the first tipping point, we cannot have confidence we will escape
others and still others. What we face, in short, is perpetual adaptation—
the task of making a wholesale adjustment to our reality, then doing it
again … then doing it yet again . It would be beter if we admited that if
we make the necessary changes too late, we will have to adjust radically,
and at uneven and unpredictable intervals, for as long as we can imagine .
That prospect is quite dire. But we should not therefore leap to the
popular image of a planetary catastrophe. The future we face is not as
simple as a full-out, planetary disaster that will simply defeat us. If that
were the case, it would indeed make all our efforts vain, all our best strate-
gies hopeless. But climate change is not a single, devastating event, like
a nuclear holocaust. If irreversible, devastating climate change takes
place, in the long term it will displace many societies, change the ethos
of our cultures profoundly, cause untold suffering to millions of people,
and reduce the Earth's population by a major fraction. It will do so over
generations, altering the world decade by decade, allowing us to accom-
modate certain changes and be defeated by others. As a result, it will not
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