Scientists have discovered a potent new greenhouse gas in the upper atmosphere that could increase global warming.

British researchers stumbled across gas the while they were studying other greenhouse gases.

Their findings have been reported in the journal Science.

The gas, Trifluoromethyl sulfur pentafluoride, is 18,000 times better at trapping heat than the most common greenhouse gas, carbon dioxide.

Greenhouse gases prevent heat escaping into space from the Earth's upper atmosphere, so as a result, the planet warms up.

Human cause?

One of the authors, Dr Bill Sturges from the University of East Anglia in England, says only tiny amounts of the gas have been detected in the atmosphere, and he believes it has only been present for the past 40 years.

That, he says, suggests it is a by-product of a human activity; possibly generated by high voltage equipment. Apart from its heat-trapping abilities, the new gas is also thought to be very long-lived.

Because it takes a long time for detectable levels of any gas to build up in the stratosphere, only long-lived, stable gases which are not easily broken down into simpler compounds tend to be found there.

But, although the gas is both a potent greenhouse gas and long-lived, Dr Sturges says its current low levels are unlikely to have a significant effect on global warming.