Professor Ross Garnaut, a government adviser on climate change, is urging his fellow Aussies to serve kangaroo meat in place of beef or lamb, because the marsupials produce negligible amounts of environmentally damaging methane gas. On the other hand, cattle and sheep, according to Garnaut's 620-page study, produce a considerable amount of methane gas through belching and flatulence, and are among the millions of livestock responsible for approximately 67 percent of agricultural greenhouse gas emissions. In order to help the environment, he proposes that Australia, which is one of the world's largest per-capita producers of greenhouse gas emissions, should decrease its cattle and sheep populations by seven million and 36 million respectively, and increase its kangaroo numbers from 34 million to 240 million by 2020. The study cites other benefits, too: kangaroo meat is low in fat and high in protein levels, and the animals survive better in times of drought.