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Pollution could be the key to finding extra terrestrial life, researchers have claimed.

They say that the pollution spewed out by other civilisations could help us find them.

They even say advanced lifeforms could intentionally raise levels to warm up inhospitable planets.

In this artist's conception, the atmosphere of an Earth-like planet displays a brownish haze - the result of widespread pollution. Pollution could be the key to finding extra terrestrial life, researchers have claimed.

New research by theorists at the Harvard-Smithsonian Center for Astrophysics (CfA) shows that we could spot the fingerprints of certain pollutants under ideal conditions.

This would offer a new approach in the search for extraterrestrial intelligence (SETI).

'Humanity is on the threshold of being able to detect signs of alien life on other worlds.

By studying exoplanet atmospheres, we can look for gases like oxygen and methane that only coexist if replenished by life,' the researchers say.

However, they do also warn the global warming could brand us 'unintelligent life' in the eyes of others.

'We consider industrial pollution as a sign of intelligent life, but perhaps civilizations more advanced than us, with their own SETI programs, will consider pollution as a sign of unintelligent life since it's not smart to contaminate your own air,' says Harvard student and lead author Henry Lin.

'People often refer to ETs as 'little green men,' but the ETs detectable by this method should not be labeled 'green' since they are environmentally unfriendly,' adds Harvard co-author Avi Loeb.

The team, which also includes Smithsonian scientist Gonzalo Gonzalez Abad, says that the upcoming James Webb Space Telescope (JWST) should be able to detect two kinds of chlorofluorocarbons (CFCs)  ozone-destroying chemicals used in solvents and aerosols.

the upcoming James Webb Space Telescope (JWST) should be able to detect two kinds of chlorofluorocarbons (CFCs) ozone-destroying chemicals used in solvents and aerosols.

They calculated that JWST could tease out the signal of CFCs if atmospheric levels were 10 times those on Earth.

A particularly advanced civilization might intentionally pollute the atmosphere to high levels and globally warm a planet that is otherwise too cold for life.

While searching for CFCs could ferret out an existing alien civilization, it also could detect the remnants of a civilization that annihilated itself.

Some pollutants last for 50,000 years in Earth's atmosphere while others last only 10 years.

Detecting molecules from the long-lived category but none in the short-lived category would show that the sources are gone.

'In that case, we could speculate that the aliens wised up and cleaned up their act.

'Or in a darker scenario, it would serve as a warning sign of the dangers of not being good stewards of our own planet,' says Loeb.