Dear Umbra, Could you help me clear up a rumor about cars? I've heard that although hybrids reduce your carbon footprint because they use less gas, the process for mining the nickel in the hybrid batteries produces far more pollution than the process for regular car batteries. So are we really making a difference by buying hybrids? I personally decided to get a more fuel-efficient car and bought a used Honda Fit, which I love. Did I make the right choice? Kimberly W.,
Raleigh, N.Y.

Dear Umbra, I'm in need of a new car. I'd love to get a Prius, but I often need more passenger seats than the Prius has. What is the most environmentally friendly and responsible choice for a driver who needs a larger car? It seems like the bigger hybrids (i.e., the Toyota Highlander) are expensive and don't get very impressive gas mileage compared to the Prius. Are there any industry plans to make SUVs that get more miles per gallon? What do I do in the meantime? Where is the minivan hybrid for us carpooling moms? Julie E.,
Los Angeles, Calif.

Dear Umbra, I've noticed lately that Method cleaning products are now being sold in a number of different retail outlets, whereas before they were only sold in Target. This shouldn't seem too weird in our every-store-sells-the-same-thing world, but seeing these products on the shelves in Whole Foods got me wondering more about them. You see, I went looking for some trusty Bon Ami cleaner the other day and found it gone from the shelves and many Method products in its place.

Dear Umbra, I saw an infomercial late at night about these foot pads that you wear to sleep and they will "remove toxins from your body." I didn't know who else to ask, so you win that lottery. Do we actually have that many toxins in our body? And does wearing silly pads on our feet really pull them out so we can easily throw these toxins in the trash? I think you should do an experiment and let me know if I'm missing the boat by not ordering right away -- or if I should save energy that will be used by ordering, shipping, and discarding used foot pads. Elizabeth,

Dear Umbra, In all sorts of corporate environmental reports, you see claims that compare apples to oranges -- "By reducing our emissions by X pounds this year, we've saved the equivalent of 17 gazillion trees." Or "If every person in the U.S. bought our eco-friendly product, we could save all the baby harp seals." OK, perhaps I exaggerate a little bit. But where do people come up with these eco-unit conversions?

Dear Umbra, My name's Jon and I'm a diet pop addict. My diet right now is 70-80 percent local, organic, or both, but I just can't help myself when it comes to getting my fix. I drink several 20-ouncers a day of diet and just can't seem to stop. Is my habit hurting the earth? Common sense says that water from my stainless steel canteen is a whole lot better than chemicals from a plastic bottle, but my addict brain is grasping at straws, hoping that diet pop is one of those rare exceptions. Jon B.,
Lakewood, Ohio

Dear Umbra, I know CO2 is a gas as other greenhouse gases are, and gases are sometimes lighter than air. So I'm wondering: how can gases be weighed in tons? That's a hell of a lot of gas to weigh even one ton, let alone the millions of tons that are reported to be causing climate change. (No, I'm not Oklahoma Sen. James Inhofe in disguise.) James N.,
Oklahoma City, Okla.

Dear Umbra, Your recent answer to the plane/train question prompts me to ask something that has always bothered me but that my little old brain can't figure out on my own. I know that planes are worse than other forms of transportation, but the plane is going to fly whether I'm on it or not. So I always wonder if it's really better for me to drive to Chicago in my car than it would be to grab an empty seat on a plane that's already going that way. In that sense, isn't it like the bus?

Dear Umbra, I have been wondering for years now -- with the hot trend toward hybrids and the new "clean" diesels hitting the market, why doesn't anyone talk about a diesel hybrid? Sounds like the best of both worlds to me. Just think: a hybrid running on biodiesel! Is this in the works? Mike H. ,
Saranac Lake, N.Y.

Dear Umbra, I want to reduce my carbon footprint. I already take a commuter train to work, but the station is down a steep hill from my house, so I drive the first mile or so in the morning and back up the hill at night. The train station has lock-ups for cycles and I'm interested in that -- but I have a disability that affects my whole right side, arm, foot, leg. I'm not able to stay balanced on a conventional two-wheeled bike but have seen specialty adult-sized tricycles around town -- mostly pedicabs for tourists.