Investing in the planting of trees, renewable energy and other carbon-offsetting practices are smart steps toward reducing global warming. Unfortunately, the purchasing of "carbon offsets" for the purpose of balancing your otherwise carbon-heavy footprint is often a capricious practice. The impact of certain carbon offsets are difficult to predict. As a result, measuring their value is often unreliable. The best way to go green remains to change your behavior, and probably not to purchase offsets.