The term "green cruising" might seem like an oxymoron for an industry that some say pays little attention to the natural resources that (quite literally) fuel its success.Despite the bad rap, cruise lines continue to make important strides to improve their environmental policies -- some lines more extensively than others. Whereas recycling, incinerating and waste-processing were cutting edge on cruise ships just over a decade ago, such processes today are basic and expected.Green technologies are being incorporated into newly built ships and are sometimes retrofitted onto older ones -- think solar panels, exhaust "scrubber" systems that help minimize emissions, advances in hull design that let ships cut through the water more efficiently, cooking oil conversion systems and energy-efficient appliances. Some cruise lines also collaborate with nonprofit organizations and government agencies to collect data about the ocean's health and climate changes.Here is a summary of the latest green practices of the major mainstream and luxury cruise lines.