Global Warming Is Irreversible, Study Says
by Richard Harris
January 28, 2009.

All Things Considered, January 26, 2009 · Climate change is essentially
irreversible, according to a sobering new scientific study.

As carbon dioxide emissions continue to rise, the world will experience more and
more long-term environmental disruption. The damage will persist even when,
and if, emissions are brought under control, says study author Susan Solomon,
who is among the world's top climate scientists.

"We're used to thinking about pollution problems as things that we can fix,"
Solomon says. "Smog, we just cut back and everything will be better later. Or
haze, you know, it'll go away pretty quickly."

That's the case for some of the gases that contribute to climate change, such as
methane and nitrous oxide. But as Solomon and colleagues suggest in a new
study published in the Proceedings of the National Academy of Sciences, it is not
true for the most abundant greenhouse gas: carbon dioxide. Turning off the
carbon dioxide emissions won't stop global warming.

"People have imagined that if we stopped emitting carbon dioxide that the
climate would go back to normal in 100 years or 200 years. What we're showing
here is that's not right. It's essentially an irreversible change that will last for
more than a thousand years," Solomon says.

This is because the oceans are currently soaking up a lot of the planet's excess
heat — and a lot of the carbon dioxide put into the air. The carbon dioxide and
heat will eventually start coming out of the ocean. And that will take place for
many hundreds of years.

Solomon is a scientist with the National Oceanic and Atmospheric Administration.
Her new study looked at the consequences of this long-term effect in terms of
sea level rise and drought.

If we continue with business as usual for even a few more decades, she says,
those emissions could be enough to create permanent dust-bowl conditions in
the U.S. Southwest and around the Mediterranean.

"The sea level rise is a much slower thing, so it will take a long time to happen,
but we will lock into it, based on the peak level of [carbon dioxide] we reach in
this century," Solomon says.

The idea that changes will be irreversible has consequences for how we should
deal with climate change. The global thermostat can't be turned down quickly
once it's been turned up, so scientists say we need to proceed with more caution
right now.

"These are all ... changes that are starting to happen in at least a minor way
already," says Michael Oppenheimer of Princeton University. "So the question
becomes, where do we stop it, when does all of this become dangerous?"

The answer, he says, is sooner rather than later. Scientists have been trying to
advise politicians about finding an acceptable level of carbon dioxide in the
atmosphere. The new study suggests that it's even more important to aim low. If
we overshoot, the damage can't be easily undone. Oppenheimer feels more
urgency than ever to deal with climate change, but he says that in the end,
setting acceptable limits for carbon dioxide is a judgment call.

"That's really a political decision because there's more at issue than just the
science. It's the issue of what the science says, plus what's feasible politically,
plus what's reasonable economically to do," Oppenheimer says.

But despite this grim prognosis, Solomon says this is not time to declare the
problem hopeless and give up.

"I guess if it's irreversible, to me it seems all the more reason you might want to
do something about it," she says. "Because committing to something that you
can't back out of seems to me like a step that you'd want to take even more
carefully than something you thought you could reverse."

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