COPENHAGEN -- Climate-change heavyweights U.N. chief Ban Ki-moon and Nobel prize winner Al Gore urged more than 500 business leaders on Sunday to lend their corporate muscle to reaching a global deal on reducing greenhouse gases.

The CEOs of PepsiCo, Nestle, BP and other major world businesses began meeting in Copenhagen, where politicians will gather in December to negotiate a new U.N.-brokered climate treaty.

"We have to do it this year. Not next year. This year," Gore said. "The clock is ticking, because Mother Nature does not do bailouts."

"Continuing to pour trillions of dollars into fossil-fuel subsidies is like investing in subprime real estate," Ban said. "Our carbon-based infrastructure is like a toxic asset that threatens the portfolio of global goods, from public health to food security."

The three-day World Business Summit on Climate Change is a precursor to the negotiations to determine what will succeed the Kyoto climate treaty that expires in 2012.