Alex Harvey, a Canadian protester, said the demonstration aimed to raise awareness of the aviation industry's contribution to the emission of greenhouse gases, a major contributor to climate change.
"Any interruption to the flow of passengers and traffic going in and out will have an impact on the airport"
Shaun Cowlam, British Airports Authority, Heathrow's operator
She said: "We need to think: is a habitable future necessary? 150,000 people around the world are already dying from climate change – that's the thing we need to be balancing out against easy access in and out of London.
"The floods that we saw last month are just a taste of things to come."
The protesters said their action was peaceful and they will not attempt to trespass on to Heathrow's runways.
Shaun Cowlam, of the British Airports Authority (BAA), Heathrow's operator, told Al Jazeera that the protest had the potential to disrupt the airport's services.
"Heathrow airport is a very complex and busy operation and any interruption to the flow of passengers and traffic going in and out will have an impact on the airport," he said.
Heathrow has four terminals, with another due to open next year.
The British government has also suggested adding a third runway to the complex.
Airlines across the world carried 4.4 billion passengers last year on more than 72 million flights.
The Airports Council International predict a growth of four per cent on that number in the next 20 years.
"The floods that we saw last month are just a taste of things to come"
Alex Harvey, Canadian protester
Sixty-eight million passengers fly from Heathrow each year.
Chris Goater, of the UK airport operators association, said total greenhouse gas emissions from passenger aircraft are only a small percentage of the overall total of such gases.
"If you look at the current contribution of aviation to climate change, it's around 1.6 per cent. [It is] a very low percentage," he said.
"[It is] a growing percentage but even by about 2050, it will be less than five per cent."
Campaigners against the expansion of the airline industry say greenhouse gases from aircraft are more problematic to the Earth's atmosphere because of the stratospheric height at which they are expelled.