A few weeks ago, we pointed to some preliminary research suggesting that Mars was going through a "global warming" phase, noting that, if true, this might give us another data point about the relative strength of natural triggers for observed global warming on Earth. Fortunately, RealClimate comes to the rescue again, with a sharp post going over the Mars data in more detail. In short: the observed 3 year shrinkage of the south polar ice cap looks to be the result of a combination of regional topography and variations in dust storms, not external solar factors.
I wondered how likely it might be that bacteria present on previous Martian probes could reactivate and affect the planets environment. It sounds crazy, but scientists have proved that such hitch-hikers can survive a moon mission - why not Mars? Could we be terra-forming other worlds already without realising it? It's just an idea, like!