There's an article out in this months' Nature on Martian Global Warming (editor's summary). I don't have access to read the Nature article. There a short article from Reuters on CNN's website.
It's interesting how they throw this in the following commentary:
"On Earth, carbon dioxide traps infrared radiation which can affect global climate. This a phenomenon is known as the greenhouse effect. Fossil fuel emissions add to the problem."
I wonder if the Nature article made that claim.