Time's Up - Stolen Future, Broken Present: The Human Significance of Climate Change - page 37

before asking for change? Why not bring everybody on board before rushing
into action?
here are eight good reasons why time is up.
First of all, the target—cuting emissions 80 percent by 2050—was
chosen for political reasons, not on the basis of the science. 2050 is far
enough away to make deep cuts politically palatable. Whenever peo-
ple suggest that we have to make these cuts earlier, others resist—not
because of the science, but because they fear the political consequences.
Unfortunately, the change in Earth's climate doesn't particularly care
about what is palatable to us. The goals we once set are too far away; if we
are honest, we must acknowledge that we must act much sooner.
Second, the science itself has changed since the international negotia-
tions began. Over the past twenty years or so, scientists have been asking
what would happen if we doubled the preindustrial level of atmospheric
carbon dioxide—around 275 parts per million—to around 550 ppm.
This number, chosen in part as a convenient signpost, has determined
the shape of countless investigations of climate change as well as much
of the discussion of potential future scenarios in the IPCC assessments.
As a result, for many years we did not have a sure sense of how much
change might take place at lower levels. In a rather different vein, those
seeking international agreements initially chose 450 ppm as a target in
part because it once seemed that with concerted effort the international
community might be able to meet it.
But in the last four or five years, further research suggests that these
numbers are too high. One paper (authored by James Hansen and many
others) published in September 2009 argues that previous models failed
to take into account the effect of positive feedback loops. Models once
predicted that a doubling in carbon dioxide concentrations in the atmo-
sphere would lead to a temperature increase of around 3° Centigrade
(with a range of from 2 to 4.5°). But current models that include the
effects of positive feedback loops estimate that the same carbon diox-
ide concentration will lead to an increase of around 6° Centigrade (with
a range of from 4 to 8°). The implication of this argument is that the
widely known and cited estimates of the IPCC are too optimistic—and
that in fact we have already gone beyond what the planet can tolerate. If
Rajendra Pachauri thought we have until 2012, these researchers imply