SAN FRANCISCO, Calif. — More than 1,400 companies and attendees gathered this week to explore the future of the U.S. greenhouse gas emissions trading market, which many say has the potential to dwarf its European counterpart.

Carbon Forum America, organized by International Emissions Trading Association and KoelnMesse, brought together experts and companies to discuss the opportunities and challenges of tackling climate change through the transition toward a low-carbon economy.

Several themes emerged, such as the ways in which the uncertainty of future U.S. carbon legislation is impacting the carbon market, as well as a general agreement among panelists that a cap-and-trade system will spur more emissions-reducing innovation than a carbon tax.

Some said the uncertainty is causing many to stand on the sidelines waiting for a signal as to how future U.S. carbon regulation will take shape.

"It's too early to take positions in the U.S...we want to be here when the market starts," said Karen Degouve, head of the European Carbon Fund, in a discussion exploring strategies for investing in foreign and domestic greenhouse gas markets.

All presidential candidates favor a cap-an-trade system, many pointed out, and this year, the Senate could vote on the Lieberman-Warner bill, which would limit emissions and introduce a cap-and-trade. But the uncertainty extends to where the emissions cap will be set and how emissions reductions will be allocated.

It is also unclear which sectors will be included in a future U.S. emissions trading program. For instance, the European Union's Emissions Trading Scheme covers the energy, metals, minerals and pulp and paper industries, with future plans to bring in other sectors, such as aviation.

Worldwide, carbon trading reached $60 billion in 2007, and could one day hit $300 billion in the U.S., according to IETA president and CEO Henry Derwent, who in a statement described Carbon Forum America as a vote of confidence in U.S. emissions trading.

"This event -- twice the size of any previous event in the U.S. -- shows that interest in emissions trading in the U.S. is rapidly approaching the levels in the heart of of Europe's emissions trading scheme, where we have been holding huge carbon finance trade fairs for the last five years," Derwent said.