High oil prices, the economic recession and a move toward energy efficiency are the likely suspects in the decline of greenhouse gas emissions in the 10 states participating in the Regional Greenhouse Gas Initiative (RGGI).

Research and consulting firm Point Carbon estimates emissions in RGGI states dropped nearly 9 percent in 2008 compared to the year before, which will lead to millions of over-allocated carbon allowances for the country's first greenhouse gas cap-and-trade.

"These results would leave RGGI long by 31.8 million allowances if emissions remain stable in 2009," Emilie Mazzacurati, Manager of Carbon Market Research North America at Point Carbon, said in a statement.

RGGI hasn't released 2008 emissions data yet so Point Carbon based its figures on power plant emissions data collected by the U.S. Environmental Protection Agency. It found six of the 10 states will have emissions declines ranging from 5 percent to 17 percent, including: Connecticut, Delaware, Massachusetts, Maryland, New Jersey and New York.

Point Carbon's estimates would put emissions nearly 17 percent below to the RGGI cap of 188 million metric tons of CO2. This is in line with an earlier report produced by Environment Northeast (ENE), which estimated emissions in 2008 were roughly 16 percent lower than the cap. RGGI is intended to reduce emissions 10 percent by 2018.

At the time the ENE report was released in late 2008, the environmental group warned that low energy prices may cause an uptick in emissions, but the economic downturn and favorable weather also appear to be playing a hand in the drop, according to Point Carbon. For instance, there were between 15 and 30 percent fewer cooling degree days over the summer in both the Boston and New York areas. Point Carbon also suggested the emissions reductions may be caused by energy efficiency programs undertaken in the RGGI states over the past decade.

"In the short term, RGGI is reaching its goal of achieving a reduction of emissions beneath its target cap," remarked Mazzacurati. "Regardless, the high amount of activity in the primary and secondary markets reflects an overall bullish sentiment on carbon."

"NYC power plant" -- CC licensed by Flickr user Nucho.