The high-pitched whine of a low-flying jet engine fills the air as the camera tracks across images of shimmering glass buildings, the Towers of Mammon in an unidentified urban CBD. No, this is not the opening credits of The Apprentice, and dropping out of the sky is not UK Business Czar "Sralan" Sugar in his helicopter, but huge, hairy half-tonne polar bears. Their falls are (presumably deliberately) reminiscent of jumpers from the 911 towers and with visceral violence the poor ursine beasts crash cruelly into the concrete and tarmac with sickening thuds.

The effect is shocking; the message brutal: every short haul flight you take emits four hundred kilogrammes of carbon dioxide – the equivalent weight of an adult polar bear.

This is the new promotional film from anti-aviation expansion campaigners Plane Stupid. It's the latest in a series of climate change "shock ads" ranging from Greenpeace's now slightly dated Friday the 13th in which a hijacked plane is flown into Sizewell nuclear power station while a family playing on the beach stands agog, to the government's own recent Bedtime Stories short that ran as part of the wider, ongoing ACT on CO2 campaign.

We expect Greenpeace and Plane Stupid to be a bit more challenging in their approach, but in Bedtime Stories, as my colleague Henry put it rather eloquently it's as if the "green police" are climbing into bed with your children and telling them that, unless daddy turns the TV off standby, Mr Snuggles the dog sleeps with the fishes. Stop climate change or the puppy gets it is not exactly the best motivational message ever.

And this inevitably begs the question do these shock tactics actually work to shift the public's attitudes and behaviours? Conventional psychological theory suggests that shock ads used to work because their message wormed its way so deeply into our consciousness that we're eventually compelled to act on it. However we swiftly become desensitized and I'm pretty sure everyone is aware of the over-hyped plight of the plucky polar bear in the context of climate change and the role of flying in fuelling the phenomenon.

But maybe the ad works by ramming home this link between high-carbon short haul flights and the fate of the Arctic? Certainly it's controversial imagery will garner press interest, after all I'm writing this analytical blog for starters, and for campaigning organisations with limited budgets and only one bite at the media cherry this is crucial. However I'm still not sure it will change behaviour, the danger is that by pumping up the high octane drama of an ad, you increase the risk of viewers feeling manipulated and dismissing it as pure propaganda. Or lapsing into highly questionable failures of tact and taste in pursuit of 'edginess'.

Far more effective I believe are the Airplot campaign by Greenpeace, led by the positive, party-style property-buying intervention in Sipson or the Trains vs Planes virals from the Campaign for Better Transport.

Shock ads work best when the consequences of the behaviour we wish to change are immediate, tangible and personal such as using a condom to prevent STDs or not drink driving. They are less effective when the "costs" are long term, uncertain and shared such as with passive smoking or climate change. This is why health campaigns like Change4life on obesity have concentrated on helping people do something positive rather than dwelling on the negative outcomes of inaction.

As climate evidence mounts up and the likelihood of anything meaningful coming out of the formerly crucial Copenhagen negotiations in December diminishes with every passing day the temptation to become shriller, angrier and more shocking in climate campaigning communications will only grow. The risk is that this will simply step up the vilification of public behaviour, leading to people increasingly ignoring the very real threat of climate change and their responsibility in driving it. Now that really would be shocking.

• Ed Gillespie is co-director of sustainable communications agency Futerra.