The opponents of the Keystone XL pipeline are engaging in an undeclared war with our neighbors in Canada. They are trying their best to kill the development of the Canadian tar sands by depriving them of a refining and export facility in Texas. Without the pipeline, the crude oil cannot be refined and shipped to the Far East and the development will die. What the opponents apparently do not recognize is that Canada is free to construct a Canadian pipeline to their West Coast terminals and ship the refined products to the Asian market whether anti-pipeline folks like it or not.
If these wizards are so interested in slowing global warming, they might start a campaign to encourage the population of the United States to stop buying any product made in Asia, and particularly China. Without a major market for their products, Asia would be forced to reduce their booming manufacturing sector with a resulting reduction in energy demands, thus reducing carbon emissions. Of course, that may lead to World War III, but at least we will have some progress in reducing global warming.