The greens lobbying President Obama to block the pipeline are asking him to forgo thousands of jobs (in an election year in which jobs will could well be the major issue!) and billions of dollars in economic advantages — not to save the planet or reduce the carbon in the atmosphere, but to confer an economic and political advantage on China. If President Obama takes the green advice, the US will get almost all of the disadvantages that come from using the oil ourselves, and lose out many of the benefits.
There’s another factor that has to be weighed. Getting secure oil sources for the United States isn’t just a matter of convenience; reducing US exposure to foreign blackmail, and reducing our need to consider military interventions and other actions to protect our energy supply helps make war less likely — and allows us, all things being equal, to get along with somewhat smaller armed forces than would otherwise be required.
More, forcing China to look to less stable places than Canada for its oil transfers some of the costs of global energy security to the Chinese, and also helps tie them into the development of a rule driven global system. If the US oil supply comes largely from friendly neighbors, while China (and other US competitors) must rely on unstable, far flung sources, we are going to have more flexibility in our foreign policy and China will have so many fish to fry and cats to herd that it will be less likely to think about mounting a global challenge to the US.
Don’t expect the enviroloons to think rationally about this. We should prefer ethical oil over conflict oil. Of course, in their unrealistic fantasies, we would use no oil at all, and just power everything with windmills (ignoring the bird kill) and unicorn flatulence.
[Update a while later]
Speaking of green madness (and now anger) it looks like climate models will have to be revised. Damn those extraterrestrial causes! Can’t you just leave us green Ptolemaians alone?