When friends recently suggested we meet for Sunday brunch, I turned it into a challenge. How could we have the most fun with the smallest carbon footprint? The weather was beautiful that weekend, so I knew the plan had to involve the beach. I live only a few miles away, but the more sustainable choice was to not take my car: According to the EPA, if I drive just ten miles less each week, in a year I’ll save 500 pounds of CO2 — about as much as four trees sequester over ten years. If that doesn’t sound like a lot, consider this: If all Americans drove just ten miles less…