In an email exchange, I asked Dr. Somerville what he thought was needed in order to spark the changes the letter seeks.
He responded, “I think a dramatic shocking surprising climate event that is unambiguously due to global warming may be the only thing that motivates people and governments. Maybe a big chunk of ice sheet destabilizing and producing a significant sudden sea level rise. Unfortunately, then it may be too late, because it’s essentially irreversible; you can’t cool the world enough to make the ice re-form quickly.”
Richard C.J.Sommerville, a climatologist at the Scripps Institution of Oceanography near San Diego, New York Times, 9 Jan 2008