As the WSJ notes:
Every dogma has its day, and we've lived long enough to see more than one "consensus" blown apart within a few years of "everyone knowing" it was true. In recent decades environmentalists have been wrong about almost every other apocalyptic claim they've made: global famine, overpopulation, natural resource exhaustion, the evils of pesticides, global cooling, and so on. Perhaps it's useful to have a few folks outside the "consensus" asking questions before we commit several trillion dollars to any problem.
The letter from the Senators is here.