Although laughing gas makes up only nine percent of total greenhouse gas emissions, it carries 300 times more global warming potential than carbon dioxide, according to a study.

Yet, unlike carbon dioxide and methane, laughing gas, or nitrous oxide, has been largely ignored as a worrisome greenhouse gas.

"It can survive in the atmosphere for 150 years, and it's recognised in the Kyoto Protocol as one of the key gases we need to limit," said David Richardson of the University of East Anglia in Norwich.

Richardson presented these findings Monday at the Society for General Microbiology's 162nd meeting in Edinburgh.

The potent gas is emanating from waste treatment plants and agriculture. Its release is increasing at the rate of 50 parts per billion or 0.25 percent every year.

It can be better controlled with suitable management strategies, but only if the importance of laughing gas - nitrous oxide - as a greenhouse gas is widely recognised first.

"When faced with a shortage of oxygen, many species of bacteria can switch from using oxygen to using nitrates instead," says Richardson.

"Nitrates can support their respiration, the equivalent of our breathing, and bacteria can get energy through processes called de-nitrification and ammonification. When they do this nitrous oxide is released into the environment," Richardson said.

Municipal sewage treatment plants, landfill sites and marshy areas polluted with too much agricultural fertiliser are all places teeming with so many bacteria that there is a shortage of oxygen for all of them to survive using normal respiration alone. This means they need to use other respiratory strategies, which release nitrous oxide.

The researchers are using a combination of laboratory based studies, fieldwork and computer modelling to understand better the key environmental variables that make different micro-organisms release nitrous oxide.