The ranks of the Clean Air Climate Coalition (CACC) expanded yesterday, with four nations, the European Union and the World Bank pledging to aid the group's efforts to curb short-lived climate pollutants like black carbon, methane and hydrofluorocarbons (HFCs).

The coalition, which was first announced by Secretary of State Hillary Rodham Clinton two months ago, was originally composed of six countries: the United States, Canada, Sweden, Mexico, Ghana and Bangladesh. At its first ministry-level meeting, which took place yesterday in Stockholm, Sweden, four more nations -- Japan, Norway, Nigeria and Colombia -- joined the World Bank and European Union in adding their names to the CACC's roster.

The coalition aims to support projects and shape policies that reduce short-term pollutants, which are responsible for about 30 percent of human-caused global warming despite the fact that they typically only remain in the atmosphere for a matter of days.

"These actions should not diminish our effort to curb carbon, but these [short-term pollutants] are a big deal," said Todd Stern, U.S. special envoy for climate change. Citing a recent U.N. Environment Programme report, he said aggressive action to curb these chemicals could reduce global warming by as much as half a degree Celsius by 2050.

Black carbon, also called soot, is a common byproduct of burning organic matter, like wood or peat -- still a common source of heat and cooking energy for much of the developing world. Methane produced from human activities derives from a number of sources, including agriculture, landfills and industrial leakage.

Small sources can be big warmers

HFCs are chemicals used in the manufacture of refrigerators and air conditioners, and while relatively small in terms of atmospheric concentration, are more than 1,000 times more effective than carbon dioxide at trapping heat.

Because the sources of these emissions are widely disparate, the CACC expects to work primarily on a policy level to create a broad base of change around the world, Stern said.

"There are lots of projects going on the ground right now," he added. However, "larger-scale activity would certainly be [the CACC's] preferred medium."

At the same time, delegates at yesterday's meetings gave a green light to a number of initiatives that can curb and are curbing short-term pollutants immediately. They include actions to reduce diesel emissions from heavy-duty vehicles, upgrades to inefficient brick kilns used widely in Mexico and Bangladesh, and accelerating research into alternatives to HFCs.

Along with its new membership, the CACC received a boost in funding from Norway and Sweden, which each pledged around $1.5 million, said Stern. That brings the program's total funding to around $18 million, with another $12 million pledged by the United States and $3 million by Canada.

The World Bank also announced that it could make $12 billion from its portfolio available to support coalition goals.