Morning roundup

Your morning list of things worth knowing.

Item the First: climate sensitivity may be lower than we'd thought; this bends optimal policy towards adaptation and away from abatement. I still think it best to have a low budget-neutral carbon tax set to ramp up on a well-announced schedule, but with flexibility to twist the schedule up or down as we learn more about climate sensitivity.

If such estimates were right, they would require revisions to the science of climate change and, possibly, to public policies. If, as conventional wisdom has it, global temperatures could rise by 3°C or more in response to a doubling of emissions, then the correct response would be the one to which most of the world pays lip service: rein in the warming and the greenhouse gases causing it. This is called “mitigation”, in the jargon. Moreover, if there were an outside possibility of something catastrophic, such as a 6°C rise, that could justify drastic interventions. This would be similar to taking out disaster insurance. It may seem an unnecessary expense when you are forking out for the premiums, but when you need it, you really need it. Many economists, including William Nordhaus of Yale University, have made this case.

If, however, temperatures are likely to rise by only 2°C in response to a doubling of carbon emissions (and if the likelihood of a 6°C increase is trivial), the calculation might change. Perhaps the world should seek to adjust to (rather than stop) the greenhouse-gas splurge. There is no point buying earthquake insurance if you do not live in an earthquake zone. In this case more adaptation rather than more mitigation might be the right policy at the margin. But that would be good advice only if these new estimates really were more reliable than the old ones. And different results come from different models.

Item the Second: All that stuff about food deserts? Probably not worth worrying about. And fast food outlet concentration likely doesn't matter either.

The researchers, who reported their findings in last week's journal Preventing Chronic Disease, looked at the habits of 97,678 adults in the California Healthy Interview Survey, and their weight, body mass index, and other indicators such as income.

They overlayed a map to determine the number of fast-food places, full-service restaurants and various kinds of food stores within five ranges, from half a mile to three miles from home.

“Evidence is more tentative than often presented in the news media and in policy arguments” linking obesity with the food environment, the researchers said. That is, the idea that people who live close to lots of fast-food outlets and far from big, well-stocked supermarkets are more likely to be overweight or obese, or to show other health results of poor eating habits.

“The evidence is not clear on whether promoting or discouraging a particular type of food outlet is an effective approach to promoting healthful dietary behavior and weight status,” the researchers said. Los Angeles has tried legislating the types of food outlets in South L.A. to help bring down obesity rates.

Caveat: I've not had a chance to read the underlying paper. And there are all kinds of endogeneity problems in this general line of research: it's hard to find an instrument for fast-food outlets' opening, and you need one to sort out the endogeneity problem if there is any correlation: do fast-food outlets cause obesity, or do fast-food outlets open in places where a lot of obese people live? But, the LA Times reports they found only weak association between location and outcomes; they put it down to that most people are able to drive to get what they want.

Item the Third: Suppose your company's parked van gets hit by another driver, pushing it into a restricted parking space. And the other driver reports it to the police. Would you expect the police to call you to let you know your van had been smashed up? Or that they'd call Council who'd send out the tow-truck for parking violations? If you live in the UK....

Item the Fourth: Bicycle helmet laws still cost lives on net. Here's a website run by cycle campaigners pointing to the literature on it. Here's a town in Washington State that dropped its helmet law because Council worried about an interesting kind of legal liability.

For 15 years, until June 1, Milton, population 7,000, 45 minutes south of Seattle, required helmets for all bicyclists and skateboarders. But with its 12-officer police force stressed by an increase in domestic violence, alcohol abuse and property crime, all of which surged through the recession, law enforcement priorities now go way beyond hectoring people about their headgear.

And an inability to enforce a law on the books, the town’s insurance consultant argued, created administrative unevenness that — in the event of an accident by someone who was not nagged or cited about helmet use — posed a liability risk that could bankrupt the community with one swipe from a punitive-minded jury.

For once, silly jury verdicts have had a beneficial chilling effect. HT on Item 4 to Greg Dwyer.