Greenhouse gases and our perception of risk

On Monday, Columbia University economist Jeffrey Sachs  told an audience at the Asia Society in New York City that, given China's dependence on coal to fuel economic growth – and its determination to grow – the United States has no option but more nuclear energy and carbon sequestration. (Here's Grist's account.)

In some ways, that seems fair enough. According to the World Resources Institute, the US is responsible for 29 percent of all human-emitted greenhouse gases (GHGs) for the past 150 years. That's a larger share than any other single country, and more than triple what China, the second largest climate offender, has contributed so far. (See Greenpeace's new report "America's Share of the Climate Crisis.")

The by-country breakdown raises the question, though: Why can't nations be responsible just for what they've emitted historically? Why can't we just clean up our own respective messes?

Because Earth's climate doesn't work like a bank. Customers can't deposit and withdraw GHGs at will and expect the whole structure to remain stable. Who has contributed what, when matters less than how much there is total, and at what point the whole system will go over some tipping point.

On this last point – the risk that GHG build-up could set off relatively rapid and rather unpleasant changes – James Hansen, head of NASA's Goddard Institute for Space Studies, warns that we've already gone too far.

Some years ago, scientists thought stabilizing atmospheric CO2 at 550 ppm would work. Then the figure became 450 ppm. Now Dr. Hansen argues that it's got to be 350 ppm. We're currently at 385 parts per million. We need to backtrack, he says. (Here's more on the science and the "350" rallying cry.)

Hansen's argument [PDF] is essentially about avoiding bad gambles. He says that the specter of what we don't know – how and when Earth's climate system goes over these thresholds – combined with what we do know (that it has gone over these thresholds in the past and that these changes correlate with GHG concentrations) represent an unacceptable risk.

He notes that climate is already changing –  a poleward shift of midlatitude deserts and the melting of mountain glaciers  – and that many of the changes are coming faster than scientists predicted.

"Impacts of this climate shift support the conclusion that 385 ppm CO2 is already deleterious," he wrote [PDF] last year.

Harvard economist Martin Weitzman breaks the unknown down into economic terms. He says that, even when the probability of a catastrophe is small, if the catastrophe is potentially great – like sea level rise inundating coastal cities and a mass extinction of some life-forms that fail to adjust – then the best investment is acting now to avoid that not-very-likely but potentially game-changing outcome.

He writes [PDF]:

"However measured, the planetary welfare effect of climate changes that might accompany mean temperature increases from 10 degrees C up to 20 degrees C with probabilities anything remotely resembling 5 percent down to 1 percent implies a non-negligible probability of worldwide catastrophe."

When confronting other – some might argue lesser – risks, the US and people in general, are quick to act. Take the war in Iraq. Issues of flawed and/or cherry-picked intelligence aside, the US decided that the costs of not removing Saddam Hussein, who was ostensibly seeking nuclear weapons, outweighed the price of going to war. The country acted to the tune of $3 trillion.

Says Weitzman [PDF]:

"On a US. national level, rough comparisons could perhaps be made with the potentially huge payoffs, small probabilities, and significant costs involved in countering terrorism, building antiballistic missile shields, or neutralizing hostile dictatorships possibly harboring weapons of mass destruction."

So, what's different about how we perceive climate change, which has led, many feel, to not much action so far?

It's not a problem of being unaware. A 2005 survey [PDF] by Yale's Anthony Leiserowitz indicates that while Americans are very aware of climate change, they think that it's happening somewhere else to someone else.

"Americans perceived climate change as a moderate risk that will predominantly impact geographically and temporally distant people and places," writes Dr. Leiserowitz.

A spate of recent studies indicates just the opposite – sea level rise from melting polar glaciers will, it seems, hit North America particularly hard.

But the deeper question is, why do we perceive certain risks – such as flying in a plane – the way we do, while greater ones – like driving in a car – don't inspire the same urgency?

A quick glance at Wikipedia's entry for "risk perception" yields some intriguing possibilities. People prefer running the risk of an unkown loss (a car crash) to paying for a known loss (car insurance), for example.

We think that things that we can imagine are more likely than things we can't. And if a perceived risk fails to induce the enough dread –  if you can't imagine it – it won't cause risk-aversion activity.

And, in fact, Leiserowitz's study [PDF] of viewers of the 2004 climate change disaster movie "The Day After Tomorrow" indicates that simply having the mental imagery to work with makes a big difference. After they watched the movie, people were much more worried about climate change.

But there's a flip side to all this. Sometimes the mental imagery we associate with a risk is so powerful that it causes risk-averse tendencies greater, perhaps, than what's warranted. In the same paper, Leiserowitz notes that this has been the case with nuclear energy for three decades.

He writes [PDF]:

[T]he dramatic portrayal of a nuclear accident in The China Syndrome (1979), combined with the subsequent real-world accident at Three Mile Island, arguably shaped the public debate about the safety of nuclear power. This synergism of fiction and reality may have greatly amplified the perceived risk of nuclear power, with ripple effects that still reverberate in public opinion and fundamentally constrain the industry today.

That doesn't bode well for Jeffrey Sachs's emphasis on nuclear.