Cash for Clunkers could have the same effect on global warming pollution as shutting down the entire country — every automobile, every factory, every power plant — for an hour per year. That could rise to three hours if the program is extended by Congress and remains as popular as it is now. Climate experts aren’t impressed. Compared to overall carbon dioxide emissions in the U.S., the pollution savings from Cash for Clunkers do not noticeably move the fuel gauge. Environmental experts say the program is not an effective way to attack climate change.