A debate is heating up in the U.S. Senate this week on global warming. It's about time.

At issue is the Climate Security Act, which would require manufacturers, utility companies and others to cut emissions by shifting from fossil fuels to greener, and more expensive, renewable energy sources.

The bill, sponsored by Sens. John Warner, R-Va., Joe Lieberman, I-Conn., and Barbara Boxer, D-Calif., would require about an 18 percent cut in greenhouse gas emission by 2020 and a two-thirds reduction from 2005 levels by 2050.

The bill for the first time puts a bipartisan plan on the table for significant steps to fight global warming.

But the bill won't be an easy sell. President Bush said he would veto any climate change bill that could adversely affect the economy.

The changes won't be cheap. But the cost of inaction is devastating. The choice is a "no-brainer," Frank Ackerman, an economist at the Global Development and Environmental Institute at Tufts University, told the New York Times: "How do you price the increased deaths and losses of endangered species and unique habitats and the increased damage from hurricanes that are becoming more intense?"

Indeed, the White House's own study released last week shows troubling trends ahead. For starters, a spike in heat-related deaths from climate-worsening smog; worsening water shortages for both agriculture and urban users and pumped up energy consumption that would be required to cool a fast-warming planet.

And last week, The Union of Concerned Scientists — a group of 1,700 scientists, including six Nobel prizewinners and 31 members of the National Academy of Sciences — called on the U.S. to cut its carbon emissions 80 percent by 2050, to avert the most dire effects of climate change.

Now it's up to the Senate to set a sensible course, before the ever-narrowing window of opportunity to make a difference truly slams shut.