AMSTERDAM—Even after the U.S. and China set targets this week for reducing greenhouse gas emissions, the world’s combined pledges ahead of next month’s climate summit fall far short of what experts say is needed to avert dangerous global warming.

Still, emission promises by the two countries, the world’s biggest polluters, added much-needed momentum as governments began final preparations for the 192-nation conference in Copenhagen, where parameters will be set for a new climate change agreement.

From Beijing to Trinidad, governments huddled Friday to plan their negotiating strategies.

China hosted India and other major developing countries a day after announcing that Beijing would cut “carbon intensity,” a measure of carbon dioxide emissions per unit of production, by 40 to 45 percent by 2020, compared with levels in 2005.

The Chinese target means emissions will continue to grow as its economy expands, but at nearly half the rate they otherwise would have done.