Why Environmentalists Can't Convince Skeptics
Consider a mother talking to her kid about risk.
Whether the topic is crossing the street, talking to strangers, using the stove, driving a car, setting off fireworks, or balancing near a cliff, mom is likely to overstate the risks at least a little bit. "Ask a mom and you get a worst-case scenario." Mom is attuned to the downside; she knows what the worst possibility is and over-weights its likelihood. If you cross the street alone, she knows you'll get hit by a car. If you talk to a stranger you'll get kidnapped. And she doesn't just overweight the risks; she also under-weights the benefits - how much fun you are likely to have doing the forbidden thing, whatever it might be. And she doesn't trust her kid to judge the risks for himself.
So mom exaggerates. But the kid *knows* that mom is a worrywart, so the kid automatically discounts everything mom says. If mom says something is risky there's probably *some* risk there, but it's sensible to figure it's being overestimated by at least an order of magnitude. So you can pay a little attention to mom's worries, but not too much - you don't want to take her too seriously. And mom *knows* the kid is discounting what she says and not paying close attention, which gives mom *even more* incentive to exaggerate, which gives the kid *even more* incentive to discount.
This is a stable equilibrium. Once started, the dynamic is nearly impossible to break because it would require both parties to change at the same time.
Conversations between environmentalists and enviroskeptics have that exact dynamic. Environmentalists are "mom". They "have to offer up scary scenarios, make simplified, dramatic statements, and make little mention of any doubts", to quote Stephen Schneider. They do this partly because that's what gets publicity and funding, but they also do it because if they accurately portrayed their certainty level it would give "the other side" a reason to ignore them. So they exaggerate a bit. They also tilt the playing field in various ways. They avoid public debates, they share data and methods only with fellow travelers to the extent they can get away with this, they try to avoid even mentioning anybody on "the other side".
The skeptics know this is happening, so they discount the claims they hear made by environmentalists. The environmentalists know their claims are being discounted, so they find every excuse to build them up even more.
A stable equilibrium.