on temperature and climate systems and that these variations are rou-
tine events over the vast stretches of the planet's history. But because
those factors are relevant, scientists have worked hard to take them into
account. Looking into this very question, scientists found that an increase
in solar radiation caused the rise in temperatures up to the 1940s and that
a decrease in that intensity—possibly along with the release of aerosols
into the atmosphere, which may counteract warming—led to the global
cooling from the 1940s to the 1970s. But average sunspot activity has
not increased since then, while global temperatures have risen at a good
pace, suggesting that solar intensity is not in fact a primary factor in the
global warming of recent decades. 172 The current change in temperature
is anomalous, is taking place far more quickly than in the past, and is pri-
marily caused by human activities.
But this direct response to the objection may not do it justice.
Evidently, many people feel that if climate change has happened before,
we shouldn't get too upset if it is happening again. his atitude may
motivate responses to charts showing how much temperatures have risen
since the late 1970s: for some observers, if current temperatures remain
within the zone of temperature variation familiar in the planet's history,
what we see today is by definition not anomalous and thus not a source of
concern. 173 As a result, if they can show that current temperatures really
aren't higher today than they were at some point in the past, they feel
they have refuted the consensus view.
But this logic just doesn't hold true. If we say for the sake of argument
that the planet may have been this warm or even warmer in the very dis-
tant past, that fact does not mean that the current warming is “natural,”
part of the ordinary course of things. Nonhuman causes may have led to
great warming in another era; it doesn't follow that the current warming
is “natural,” too.
This answer is already a sufficient response. But it is interesting to try a
thought experiment as well—to take the contrarian objection at its word
and see what happens. Suppose that the current warming is “natural,” that
it is entirely the result of forces entirely outside our control. Does it really
follow that we have nothing to worry about? Rather than helping us dis-
miss climate change, this argument only reinforces the problem—and
makes it even harder for us to do anything about it.