Oil pipeline creates a political dilemma for Obama

WASHINGTON — In May, environmental writer and activist Bill McKibben — pondering a simmering energy issue — asked a NASA scientist to calculate what it would mean for the Earth's climate if Canada extracted all of the petroleum in its rich Alberta oil sands region.

The answer to McKibben's query came a month later: It would push atmospheric carbon concentrations so high that humans would be unable to avert a climate disaster. "It is essentially game over," wrote James Hansen, who heads NASA's Goddard Institute for Space Studies and is one of the nation's leading voices against fossil fuel ener...