The Cassandras of global warming blame President Bush for running a faith-based, not science-based, presidency. But it's Mr. Bush's successor who, by embracing the fight against global warming, will have to make the greatest leap of faith.

All three viable candidates for the presidency -- Sens. John McCain, Hillary Clinton, and Barack Obama -- have endorsed a so-called cap-and-trade system for carbon emissions.

That isn't just a sharp turnabout from the current administration's policy; it also could herald the biggest new regulatory initiative to be adopted in the U.S. in decades.

The idea is a response to strong science showing carbon emissions contribute to the earth's warming. There's no science, however, that can accurately predict how much economic pain will be caused as a result of their proposals. An analysis published Friday by the Bush administration concluded that carbon emissions could be capped without significantly harming the nation's economic growth over the next two decades. But the report also found that such a step could lead to sharp increases in electricity and gasoline prices.