Right, we saved the polar bears - now on to Phase 2.   There are 900 million vehicles on the planet, which thanks to modern exhaust technology, only contribute 2% of the world's nasty greenhouse gases.  There are, however, 1.5 billion cows, whose methane burps (not farts - common misconception) contribute 60% of the world's greenhouse gases.  Bad cows.  Naughty, tasty, belching cows.   The solution is obvious (to a genius like me): Put wheels and methane-powered jet engines on cows.   We f