The solution is obvious: eat kangaroos!(*) Apparently that idea isn't very palatable to most. Some undoubtedly don't like the idea because they find kangaroos cute (my daughters - no strangers to methane production themselves - fall into this category). Others won't touch the stuff because kangaroos are, effectively, giant rodents (the Chinese for a kangaroo translates literally as "pocket rat"). But a growing percentage of Australians consider the meat of this iconic animal to be not only tastier, but healthier, than beef.
But what if the idea caught on, and everyone started eating their national symbols. Would we see Roasted Eagle on American tables? Braised Bulldog on sale in English gourmet pubs? Frogs served in French restaurants (oh - hang on...)
But back to greenhouse gas emission - what are we going to do about Guinness drinkers...?
(*) Apparently not obvious enough for some scientists, who think the most logical approach is to put kangaroo stomachs into cows and sheep. I wonder if any of these guys were on the EJB committee (Nerd Humour - ignore at will)