Bond markets propel climate response.

Bond markets propel climate response.

Green bonds may help provide the $US1 trillion ($1.06 trillion) annual investments in clean energy that environmental groups say is necessary to limit the impact of climate change.

"It's catching on like wildfire," Michael Eckhart, a managing director at Citigroup and founder of the American Council on Renewable Energy, said in an interview. "We've reached the Holy Grail, which is the bond market."

More than $US16.6 billion has already been sold worldwide this year, surpassing last year's $US14 billion, as more companies issue the debt to finance clean energy projects, according to Bloomberg New Energy Finance.

Green bonds offer a simple method for investors to tap into fixed income markets and finance clean energy, including energy efficiency and sustainable business practices.

The market for the bonds could top $US40 billion this year and reach up to $US100 billion in 2015, Eckhart said on the sidelines of the Renewable Energy Finance Forum in New York.

A $US1 billion issue in February, 2013 by the World Bank Group's International Finance Corp. sold out in an hour, Eckhart said.

"We were shocked it went so fast," Eckhart said. "Pension funds love them."

A coalition of banks, including Citi, Bank of America, JPMorgan Chase, Credit Agricole and others created a common set of criteria for green bonds in January to act as a catalyst for the development of the market.

"Creditworthiness was the only criteria the bond market was using," Eckhart said. "For the first time, we're showing that where it's being spent matters."

Bloomberg