Hearings on a massive bill to curb the gases blamed for global warming are drawing to a close with some star power.

After three days of panels and testimony and more than 50 witnesses espousing on the nitty-gritty details of the 648-page draft, the grand finale on Friday will feature former Vice President Al Gore, former House Speaker Newt Gingrich and former Virginia Sen. John Warner.

All have played leading roles in the issue of climate change — even though at times they have been on opposite sides of the debate.

Gore, perhaps climate's foremost celebrity, will once again tell Congress that legislation is needed now to avert the dire consequences of climate change — among them wildfires, droughts and storms.

Gore won a Nobel Prize and starred in an Oscar-winning film about global warming, "An Inconvenient Truth." He has long blamed the appetite for fossil fuels like oil and coal for the planet's warming. In January he called on Congress to pass legislation to limit greenhouse gases this year despite a faltering economy.

Gingrich, who led the Republican-dominated House from 1995-1999, still isn't convinced that human activities are the leading cause for global warming. He was added to the lineup late Thursday at the request of Republicans.

Gingrich is against putting a price on global-warming pollution, the main mechanism in the legislation. But the former congressman thinks conservatives should play a role in crafting climate and energy policy.

Gingrich last year appeared in a commercial sitting alongside House Speaker Nancy Pelosi, D-Calif., that was paid for by Gore's Alliance for Climate Protection. In it he says that while he doesn't always see eye to eye with Pelosi, "we do agree our country must take action to address climate change."

Warner, a Republican, watched last summer as his bill to limit the gases blamed for global warming failed to get enough votes in the Senate to break a GOP filibuster. The debate focused on bitter disagreement over the expected economic costs, and similar arguments have been made this week.

The draft bill calls for a 20 percent reduction from 2005 levels by 2020, and 83 percent by mid-century. It also would require utilities to produce a quarter of their electricity from renewable sources by 2025.

This time around, there is a larger Democratic majority and a president who supports legislation to curb global warming.