The obvious caveat is that fuel efficiency and aerodynamic drag vary from car to car. But unless I had better figures for my own car, I wouldn’t feel guilty running the A/C above 50. (Well, to be frank, I wouldn’t feel guilty at even lower speeds, because my own guess is that driving in a cooler car makes you a safer driver, and the lower risk of an accident would more than justify the extra fuel consumption. But that’s just a personal guess based on no data. If anyone has any, let me know.)

The disappearance of Bangladesh. This low-lying country has been one of the prime exhibits in the horrors of sea-level rise. “An Inconvenient Truth” shows much of it underwater and warns that 60 million people in Bangladesh and Calcutta would be displaced by a 20-foot rise in sea level. Others have predicted that the whole country will disappear. Well, the sea has been slowly rising there, but scientists in Bangladesh report that the country has actually been gaining land in recent decades because the silt deposited by its rivers has more than offset the rising sea level.The scientists, according to AFP, estimate that this process could add 1,000 square kilometers in the next half-century — and perhaps an additional 4,000 square kilometers if the country continues building dykes.

I mention this not to argue that there couldn’t be bad consequences from global warming. (I think it’s potentially a serious problem and have suggested a carbon tax to reduce greenhouse emissions.) I mention these new estimates because they show how simplistic some of the doomsaying has been. Aside from using unrealistic projections (like the 20-foot sea-level rise), the catastrophists have ignored other processes that can offset some effects of global warming. And they’ve overlooked humans’ capacity to adapt — like building dykes, which has been done recently in Bangladesh and for centuries in other low-lying countries. As I wrote in a Findings column last year New York City has already experienced the kind of sea-level rise that is projected to occur from global warming, yet it has gained shoreline. My colleague Andy Revkin has more thoughts on adaptation in his post on the news from Bangladesh.

Now, back to the readers’ complaints about the nonworries in my column, like shark attacks. I cited the International Shark Attack File’s report that only one person died in a fatal attack in 2007, in the South Pacific. Some readers complained that I had ignored an attack this year. Well, there are shark attacks every year, but as the I.S.A.F. has noted, the number of fatal attacks has actually decreased in recent years despite being more people being in the water. And if you look at figures for fatal attacks over the past two decades, you see there are typically no more than six annually throughout the world.

Lots of readers said they wanted to keep worrying about plastic bags even though they probably generate fewer greenhouse emissions than paper bags. The readers said it was better to bring a reusable bag to the store. But not everyone can or will do that on every shopping trip. And if you ban plastic bags at the grocery stores, as some governments have done, the practical effect is to force more people to use paper bags for their groceries — and to buy more plastic garbage bags.

I recognize that plastic bags can be a litter problem, but so can plenty of other products — plastic and nonplastic. Why not spend time and money dealing directly with all kinds of litter rather than ban one form of it? This reminds of the debate over requiring stores to collect deposits for cans and bottles, a measure justified as a way to reduce roadside litter. But states without mandatory deposits, like Texas and Washington, showed that the most cost-effective way to reduce litter was to hire clean-up crews to pick up everything, not just cans.

And finally, I don’t buy the argument that plastic bags are worse than paper bags because they don’t biodegrade in landfills. First, landfills are so airtight that paper bags don’t quickly decompose either. Researchers who have gone digging in New York’s Fresh Kills landfill have found they can read newspapers from long ago. Experts who have done life-cycle comparisons say the paper-plastic difference isn’t enough to matter. Second, by remaining intact in landfills, plastic bags are trapping their carbon, which is good for the atmosphere. If you’re worried about global warming, you don’t want products decomposing and releasing greenhouse gases.  Read rest…