STANFORD, Calif. -- With his hands in the air, professor Mark Z. Jacobson lets out an exasperated sigh. A Twitter dispute between him and a conservative commentator is playing out in front of his 6,000 followers. The back-and-forth stems from a paper Jacobson published last year in the journal Energy & Environmental Science outlining paths for all 50 states to run on renewable energy by 2050. The paper estimated that the number of jobs created by the transition would far outweigh jobs lost in the fossil fuel and nuclear energy sectors, including construction. But the critic said that the construction jobs would go away once it's built, echoing a complaint many opponents of the Keystone XL pipeline raised about that project's job numbers.