Dear Umbra, My friend and I have been having a debate that I hope you can help us settle. What is the rule of thumb when turning off the air and opening the windows? I live in Texas and in the spring we have one or two days in a row that are cool enough for open windows followed by four that are not. Should I open the windows when it is nice only to have to close them again and turn the air on in a day or two? Does it cost more to re-cool my apartment than it …

Dear Umbra, I recently visited Moab, Utah, and found that many people there use "swamp coolers" rather than conventional air-conditioning systems. Moab is in a near-desert environment and has frequent water-shortage problems. I'm wondering whether this swamp-cooler method of air-conditioning is really greener than the systems most of the rest of us use, and whether it is depleting the already low water supply in these Southwestern desert areas. How does it stack up cost-wise against other types of cooling systems? My AC broke down this spring, and if I am able to get enough money together by next summer, I'd …

Dear Umbra, Please advise me on the best way to beat the summer heat! I live in a rather steamy studio apartment and thus far have been languishing under fans in front of the open window, lapping up ice cream, and taking many cold showers. I feel a tad guilty about the excess use of water in the pursuit of keeping cool. What's worse -- to sell out and buy an electricity-sucking air conditioner or send lots of cold water down the drain? Do you have any other chilling suggestions? Stickily, with much thanks,JoyceNew York, N.Y. Dearest Joyce, Fan-tastic. I …

Dear Umbra, I love to freeze fresh veggies at their peak of ripeness during the summer. Then, in the winter, I don't have to buy commercially frozen veggies or long-distance transported ones. In order to do more of this, I'd like to move my 1985 refrigerator to the basement and use its freezer entirely for this purpose. I would buy a new one designated Energy Star. Would this end up being environmentally a plus, a minus, or a wash? EnidAmherst, Mass. Dearest Enid, Veggie tales. Photo: USDA. Your 1985 refrigerator has passed its own peak of ripeness, as you may …

Dear Umbra, I've never appreciated human-made fabrics -- polyester and its cousins invariably feel less comfortable to me than cotton or wool. Until recently, I thought this personal preference also had the happy side effect of making me a greener clothes shopper, since producing natural fibers doesn't involve long chains of polymers. A friend recently claimed otherwise, telling me that the growth, harvesting, and shipping of cotton from around the globe (indeed, my very favorite all-cotton shirt was manufactured in Burma -- yikes!) means it does more damage to the environment than the factories that produce the artificial fabrics. Is …

Thinking outside the loft. Catch the aboveground S train in Brooklyn and you'll whiz through the neighborhood of Crown Heights, an industrial pocket of warehouses and factories that once stored and manufactured everything from artillery to pickle jars. These days, the buildings you pass appear to be abandoned relics in a bleak concrete landscape. But then, just as T.S. Eliot is coming to mind -- "What are the roots that clutch, what branches grow / Out of this stony rubbish?" -- you hurtle by a bright green oasis of richly vegetated roofs and a glossy black array of solar panels …

Dear Umbra, I'm an elementary school teacher and I'd like to get a pet fish for my classroom, but I've heard tales of such fish being caught by eco-egregious means: dynamite blasting, cyanide dumping, etc. How can I make sure I'm getting happy, healthy, sustainably caught fish for my aquarium? Ginger Dearest Ginger, Is nothing sacred? Apparently not cute aquarium fish, which are wooing consumers to inadvertently destroy remote natural environments. Fish-ful thinking. Salt-water, aquarium-destined fish are indeed caught with cyanide. The fisherperson descends to the reef and squirts cyanide into nooks and crannies, stunning the fish, which naturally become …

Dear Umbra, I'm a dedicated cineaste, and over the last decade I've built up a large library (around 5,000 titles) of classic films on VHS and old-fashioned laser discs. I have been anxious to start adding DVDs to my collection, with all the extra features they offer, but I've held off because I know that any further expansion of my collection will require me to make more space -- i.e., get rid of a bunch of bulky plastic videocassettes and laser discs. I can probably sell a few of the tapes, and donate some to a library, but I'm fairly …

Those who are quick to snub Hollywood environmental activists as dabblers in eco-chic or peddlers of a pet cause would likely have a change of heart after shooting the breeze with Laurie David. Laurie David Photo: Tierney Gearon. David began her career booking comedians for David Letterman and met her husband Larry David -- co-creator of Seinfeld and creator and star of Curb Your Enthusiasm -- when he was a no-name angling for a five-minute spot in her lineup. She went on to produce comedy specials for HBO and MTV and develop sitcoms for 20th Century Television. More than a …

Dear Umbra, I'm a conscientious baby boomer who would like to do things to help the planet. I'm simultaneously enjoying a midlife crisis. I have spent more than eight years in college, studying to be a psychologist/chef. Where in the eco-field is there a place for a reformed business owner/computer teacher/chef with years and years of experience in the psychology of women? Dr. Thom Jacksonville, Fla. Dearest Dr. Thom, Get a job that takes the cake. The "eco-field" is not a profession. It's not the Law, or Medicine, or Elementary School Teaching. The eco-field is like unto a mighty river …