Readers responded to September's special issue "Energy's Future: Beyond Carbon" like there was no tomorrow--with critiques, alternatives and prescriptions to help assure that there will be. Critical letters ranged from global warming deniers to cautious skeptics, many of whom felt it was unscientific for Gary Stix to pronounce in the introduction, "A Climate Repair Manual," that "the debate on global warming is over." Vern Porter of Elk Grove, Calif., begged to differ: "It seems potency of water vapor as a greenhouse gas is largely ignored and its capacity to moderate temperatures unappreciated."

Then there were readers who concluded that if global warming is upon us, we should strive to adapt to it rather than to reverse its effects. Others felt achieving sustainability would require humanity to surmount not only technological but also cultural hurdles, including the willingness to control population growth. The largest volume of responses, however, offered options that were not covered, from harvesting lightning to white rooftops to underground homes lit with LEDs as well as a low-tech return to using clotheslines, more rail transport and the 55-mph national speed limit.