On eve of G20 summit, Obama seeks unity

“Those who used to chastise America for acting alone in the world cannot now stand by and wait for America to solve the world’s problems alone,’’ he said.

Obama was to arrive in Pittsburgh this afternoon. The summit will conclude tomorrow afternoon.

The leaders face daunting challenges in overcoming differences on major issues, ranging from restraining bankers’ bonuses to overhauling financial regulation and plotting a course for sustainable economic growth, now that the worst of the downturn appears to be over.

As some of the leaders began arriving in Pittsburgh, yesterday, four environmental protesters rappelled off a bridge over the Ohio River, dangling perilously for a while over the water while steadying a large banner warning of “climate destruction’’ if the world’s leaders do not act to control carbon dioxide emissions.

Police said they arrested nine members of the environmental group Greenpeace, charging eight with various misdemeanors and the ninth with conspiracy.

Obama signaled he will use the G-20 summit to call for an end to extensive government subsidies that encourage the use of fossil fuels like oil, coal, and natural gas, which are blamed for contributing to global warming. He will propose a gradual elimination, White House officials said.

Mike Froman, Obama’s national security adviser for international economic affairs, said the main value of the proposal would be if other countries sign on. He declined to say whether Obama is willing to go it alone and to try to eliminate such subsidies in the United States.

Many countries, including the United States, provide tax breaks and direct payments to help produce and use oil, coal, natural gas, and other fuels that spew carbon dioxide, the chief greenhouse gas. Eliminating those would provide “a significant down payment’’ toward the US goal of cutting fossil fuel emissions in half by 2050, Froman said. The proposal, however, is likely to spark opposition from China and possibly other major greenhouse gas emitters, such as India and Russia.