I would say it is greenhouse gas. The way I look at it, we are releasing CO2 into the atmosphere that has been sequestered as petrochemicals for oodles of years. So practically speaking we are adding 'new' carbon to the carbon cycle. Carbon dioxide is a greenhouse gas, not a very strong one, but it does do it. Also, much CO2 is dissolved in ocean water, and the amount of gas dissolved in a solute depends on the temperature, and with the temperature going up, this would start to be released, adding to the effect. Also the higher temperatures would start to melt arctic permafrost, restarting the decay of long dead organic material, also leading to the release of carbon dioxide, as well as methane, which if I remember right is a 'better' greenhouse gas. Combining with the loss of polar ice caps, which would release large amounts of fresh water,as well as losing the heat reflecting (high albedo) and absorbing ( ice takes a lot of energy to melt) buffer of the polar ice, this can't be a good thing. Unless your into developing the Northwest Passage that is. Idon't think Earth will become Venus, but I don't think it will be nice.

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