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down a particular street at a certain hour, you'd face a 1 to 10 percent
chance you'd have a terrible accident? Very few of us would take that
chance. Those who insist on certainty, however, suggest that if there is
somewhere between a 90 and 99 percent chance of a crash, we should
still go down that road. After all, there is still a small chance we'd make it
through without injury.
Such a response is ludicrous. When faced with the possibility of major
harm, most sane adults would want to play it safe, to have an out, a Plan
B, or at least good insurance and excellent medical care. We aren't simply
indifferent if there is a high likelihood something horrible will happen
to us. Yet in the climate change debate, we've managed to get the whole
thing upside down. A supposed uncertainty in the science has covered
up a far more frightening uncertainty about our futures: are we going to
make it through the next few decades in good shape? Do we actually have
a future? h a t 's the real uncertainty we should face, and if we think about
it in those terms, our answer gets obvious very fast.
The question is not whether scientists have absolute proof that human
beings are causing climate change. The core question is instead whether
we are sure we are not puting our own lives and futures into doubt by
how we live, especially by how we emit greenhouse gases. Even if you
think the science on this subject could be sharper, you have to admit it's
already telling a prety dire tale. Just hanging out until the consensus is
even stronger isn't very smart.
But wait a minute, another person might object, global warming is real,
but we aren't the cause . Earth's climate has changed dramatically over its
history, thanks to any number of natural causes; our present moment is
no exception. For us to atribute climate change to ourselves is merely
a sign of our own arrogance. We live on an unstable planet, this person
might say; there's nothing we can do about that fact. The cyclic changes
in distance between the Earth and sun, the changes in the tilt of the polar
axes, and variations in the brightness of the sun all change the amount
of sunlight entering the atmosphere, alter the planet's warmth, and over
time lead to immense changes in climate.
This objection has a great deal behind it. Research has in fact dem-
onstrated, for example, that the slight changes in solar intensity (due to
sunspots and changes in the sun's brightness) have enormous effects
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