Engineering irritation
The article “Engineering a cooler Earth” (SN: 6/5/10, p. 16) was incredibly irritating. The solution to global warming is not technology of the type presented, but population and pollution control. You need to start talking about that. The longer we see the problem in technical terms, the less likely we are to even talk about the real solutions. (How many articles have you had recently discussing limiting population — that’s science, isn’t it?) Suppose we dump a bunch of chemicals in the biosphere and it cuts global temperatures a bit or holds them steady. Is that the kind of outcome we want so we can dump ever more CO2 into the atmosphere and add a billion or two more people?
Bill Amborn, West Linn, Ore.

Your article on geoengineering raised, but did not fully explore, the crucially important question of the impact of the cloud-brightening scheme on rainfall over land. Three studies have been made, by three separate groups, using three different and well-regarded models. One by Jones et al (2009) seeded a small fraction of suitable maritime clouds and reported significant reductions of rainfall over northern South America. Another, Rasch et al (2009), seeded an intermediate fraction, found no rainfall reduction in this area, and no significant rainfall reduction over land. A third, to be published by Bala et al, seeded all suitable clouds and found no rainfall reduction anywhere over land. They provided a plausible physical/meteorological explanation for this result. No categoric statement can currently be made as to whether or not the cloud-brightening scheme would reduce rainfall significantly anywhere over land.
John Latham, National Center for Atmospheric Research, Boulder, Colo.
Stephen Salter, University of Edinburgh, Scotland

ET, phone where?
It seems from your article “Can you hear me now?” (SN: 4/24/10, p. 22) that most searches for ET communications have assumed that we were looking for a deliberate signal — that we assumed ET was trying to phone us. But seriously, why should he? It would be horribly foolish to assume that ET politics resembled ours, but the allocation of resources according to priorities is a necessary preoccupation of life from the single cell on up. Yelling into the void by any of the methods described would use power that would likely be needed elsewhere. (Are we doing it on purpose?) Only the searches for leakage from ET power generation are likely to turn up anything, and they will be difficult to sort out from natural causes.

Nancy Parker , Caldwell, Idaho