Some Climatologists, such as James Hanson, believe that a runaway greenhouse effect large enough to potentially distinguish all life on earth is possible Obviously this is not a likely extinction event, but I believe it is still worth considerable resources to reduce its probability.

While little has been done legislatively to combat climate change, the Obama administration is pursuing regulatory action through the EPA to reduce greenhouse gas emissions from power plants that will make the construction of new coal fire power plants very difficult.

Additionally, the administration has benefited alternative energy industries through on climate change has increased in recent years. It's less and less likely that a Republican president would pursue policy aimed at substantially reducing green house gasses. They might also appoint a supreme court member who would rule against the regulations the EPA is attempting to implement now.

I don't think that the party who holds the presidency is the most important factor in whether we reduce carbon emissions, but it likely contributes.