Newquay Airport's owners say the future of Cornwall's economy is at stake as campaigners call for a boycott of a new British Airways service.
British Airways says it takes environmental concerns seriously
Greenpeace says the new service to Gatwick is increasing global warming through carbon emissions.
It offered passengers booked on the first flight a train ticket instead.
But Cornwall County Council says the route is crucial to the struggling airport, which is a lynch-pin for Cornwall's economy.
The 140-seat Boeing 737 flights, from the West Sussex airport to Newquay start on Tuesday, with the first flight arriving in Newquay at about lunchtime.
Loss of air services from Newquay would effectively cut off Cornwall from the rest of the UK and the wider world
The airline previously flew the route until 2003 but dropped the service, which was picked up by Air South West, saying it was making a loss.
It has said the increasing popularity of Cornwall prompted a rethink.
The county council welcomed the return of BA to Newquay, which it says is vital to the county's prosperity.
The airport has about 300,000 passengers a year and the council is hoping numbers will continue to rise to stem the airport's losses of about £1m a year.
Andrew Mitchell, economic portfolio holder for the council, said: "Cornwall is one of the poorest parts of the UK, with GDP per head at less than 75% of the UK average.
"Loss of air services from Newquay would effectively cut off Cornwall from the rest of the UK and the wider world.
"Greenpeace is ignoring the needs of ordinary people wanting to visit Cornwall, Cornish residents wanting to go on holiday and small businesses in Cornwall struggling to provide employment."
Greenpeace says air travel causes 10 times more damage to the climate than travelling by train.
But the council said passengers had paid for the social costs of carbon emitted through air passenger duty.
BA said it was providing travel for people who wanted to get from Gatwick to Cornwall in one hour, rather than the five hours it took for the London Paddington to Newquay train.
"We have improved our fuel efficiency by 27% since 1990," it said.
"We are the only airline in the world currently undertaking emissions trading and have lobbied for many years for aviation to be included in the EU emissions trading scheme."