Unless we combine to take decisive action, climate change will ravage our planet, and with it our prosperity and security. The dangers have been becoming apparent for a generation. Now the facts have started to speak: Eleven of the past 14 years have been the warmest on record, the Arctic ice cap is melting and last year’s inflamed oil and food prices provide a foretaste of future havoc.
So, higher oil prices, and the havoc caused by that, is what we want to avoid?
Consider that a Pigovian Tax is a tax applied directly to fossil fuels, intended to cover the 'externalities' in the costs of producing carbon not born by, say, a mining company that extracts the coal. It would introduced by Keynes' mentor Pigou as a way to efficiently deal with externalities like pollution, and Greg Mankiw explains its motivation here). It is liked by economists because it puts the cost of the carbon right on the carbon, making its costs focused on the source, and not spread around. It is the least distortionary method of getting people to burn less carbon: raise its price, people will substitute alternatives (wind, nuclear, sweaters). Cap and Trade is less efficient than a Pigovian tax, and all sorts of targeted taxes and subsidies less so than that (even Paul 'I'm Mad as Hell' Krugman agrees). Raising oil prices is the least distortionary solution to any effort to lower carbon burning.
So, what they highlight as an undesirable effect of Global Warming is a lower bound cost as to what would go into any solution being considered. I have a feeling the Global Warming crowd knows what they want, and are just trying to present anything motivation to get us to agree to their proposals, regardless of how inconsistent their reasoning.