U.S.-based Merrill Lynch and France's Societe General launched new carbon dioxide emissions indexes this week.

The MLCX Global CO2 Emissions Index, introduced by Merrill Lynch's research division, gives investors access to international CO2 markets established by the European Union and the Kyoto protocol. The EU Emission Trading Scheme's European Union Allowances (EUA) and Clean Development Mechanism's certified emissions reductions (CER) make up more than 99 percent of global trading activity related to greenhouse gas credits.

Société Générale's SGI-orbeo Carbon Credit Index will also provide access to the two trading schemes. Société Générale launched its index with orbeo, a joint venture between itself and chemicals group Rhodia. While Société Générale's index will weigh EUAs and CERs evenly, Merrill Lynch will give the EUAs more weight, Reuters reported.

"The weightings of the new MLCX Global CO2 Emissions Index are based on liquidity of the underlying instruments, a crucially important element for investors looking to gain exposure to a new and fast-growing market," Francisco Blanch, Merrill Lynch head of global commodities research, said in a statement.

Merrill Lynch plans to add to the offerings in its index as the global emissions market expands. Barclays Capital was the first to create an index tracking the two major CO2 markets, launching the Barclays Capital Global Carbon Index in late 2007.