A climate tipping point In Janet Raloff’s article “Forest invades tundra” (SN: 7/5/08, p. 26), there seems to be a paradox. Raloff says that the albedo from normal snow coverage of the tundra “helps maintain the region’s chilly temperatures,” implying that the coverage also preserves the mats of plant matter. A little later in the article, Ken Tape explains how the arrival of tiny shrubs traps snow, insulating and warming the soil beneath and stimulating the growth of bacteria. At what point does snow’s effect change from a chilling blanket that preserves the tundra ecology to a warming blanket that stimulates bacterial and plant growth? Doug Stuart, Glenview, Ill. Once shrubs move in, the effect can change. Although snow cover can keep the establishment of such greens at bay, if shrubs can make it in and establish roots during warmer summers, then the snow can serve as a warming blanket to help those shrubs survive harsh winters. With each successive summer,the greens can become increasingly larger solar collectors. If they become large enough, they may continue to absorb solar energy even during part of the winter—as trees are doing now in the area of the Urals discussed in the story. —Janet Raloff Go for the gold The article “Finding the golden genes” (SN: 8/2/08, p. 16) makes it sound like gene boosting is horrible and focuses entirely on those who wish to cheat in an athletic competition. Really, this is great news. I don’t want to win the Olympics; I just want access to things that may improve my quality of life. Erythropoietin is wonderful for someone with asthma. Building muscle mass is great news for seniors. Take your tired view of bioethics and darken someone else’s door. As for me, when these items become available on the black or gray market, I will be waiting, cash in hand. We are discussing my quality of life, and the bioethicists don’t get a vote. Additionally, get to work on memory- and intelligence-enhancing products. I fail to see any issues since we are all stuffing ourselves with supplements, vitamins and other enhancement products. Something that actually works would be welcome. Ralph Hoefelmeyer, Colorado Springs, Colo. Super bonding In “Small, but super” (SN: 6/21/08, p. 14), models of the superatoms are shown. I have a question on the first model (Al4H7–). You show hydrogen with two bonds. How can it have two single bonds with only one electron? Skip Hackett, Tampa, Fla.

Indeed, hydrogen can’t share electrons with more than one other atom at a time. The bonds in question are hydrogen bonds in which no electrons are shared, similar to the bonds between water molecules in ice. In this case, hydrogen atoms form two such bonds, acting as a bridge, says Shiv Khanna of Virginia Commonwealth University in Richmond. “In atom clusters, it is not unusual for hydrogen atoms to occupy a bridge site between two atoms,” he says. —Davide Castelvecchi Gender in the classroom Regarding “Girls could give preschool boys learning boost” (SN: 7/19/08,p. 14), I am wondering if any difference among the boys would have been seen had the preschool teachers been male. Elizabeth Oscanyan, Philomont, Va. This is an interesting possibility that would be hard to test, given the scarcity of male preschool teachers. —Bruce Bower Unseen whales The article “Stranded: A whale of a mystery” (SN: 7/19/08, p. 22) was disappointing because the tone and quotes implied that the whales found stranded represent the totality of the problem. For example, “We’re talking about five animals a year,” and “Fewer than 300 whale deaths can be attributed to naval sonar.” How do we know that for every stranded whale there are not many more dead ones spread across the ocean floor? Frank Lawlor, Austin, Texas The reader is correct. Part of the reason scientists have difficulty assessing how many whale deaths are associated with sonar is that only whales that are found can be counted. Even assessing live whale populations is difficult. —Rachel Ehrenberg Look at them go Regarding “Built for speed” (SN: 8/16/08, p. 14), my wife and I were on a cruise ship leaving Glacier Bay in 2003. I had my GPS set on miles per hour. Here is an excerpt from my trip journal: July 17, 2003. It’s almost 4 p.m., and we leave the bay and head west through the strait for the Gulf of Alaska. As we move along, at about 13 mph, we notice a seagull flying along beside us 30 feet or so off the water and about 100 yards out. Then there are two, then three…. The boat begins to accelerate and passes 16 mph. The gulls, seven now, are in tight formation, still 100 yards out….We are up to 22 mph, and the gulls have dropped to the wave tops but now are gaining and climbing. They begin to pull away as we top out at 24 mph, and they disappear ahead. They effortlessly cruise at whatever speed we can go.… By now our boat is at cruising speed, but I think we could put it all he way to flank speed and the gulls would still flank us. It went on for 20 minutes….No human could do that. Twenty minutes at from 15 to 25 mph is beyond our capacity. I have new respect for the lowly seagull. Steve Fletcher, Sierra Vista, Ariz.

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