The loss of the pink dolphin habitat off Lantau to reclamation for a proposed third runway would cost the city HK$36.1 billion over 10 years, a study has estimated.
Researchers added the "social cost" of destroying 650 hectares of the habitat to the loss in tourism - two possible consequences of the project.
They based their calculation method on Social Return on Investment (SROI) analyses used by London-based think tank New Economics Foundation.
An SROI study factors in the social, economic and environmental effects of a project, which traditional cost-benefit analyses usually ignore. Heathrow Airport shelved a third runway in 2010 after the foundation found such costs to be almost as high as the predicted economic benefits.
"The government tends to look at everything in monetary cost," Friends of the Earth's Melonie Chau Yuet-cheung said yesterday. "There is economic value in tourism and the livelihoods of tour providers will be ruined."
Chau's group is part of the research team that includes the Dolphin Conservation Society and the Professional Commons.
The Airport Authority said it understood the importance of dolphin conservation but would not carry out an SROI.
"SROIs are generally used to assess small community-based or charitable projects and are not applicable for large infrastructure developments," a spokeswoman said. "SROI studies also lacked international assessment standards." She said the authority would look at "all measures to minimise or alleviate the impact on dolphin habitats and dolphin-watching activities" in its environmental impact assessment.
The HK$130 billion runway is proposed to be built by reclaiming 650 hectares off the airport island. The researchers say the authority's assessment does not include a carbon audit, ecological impact assessment or complete assessment of air and noise pollution - a gap they hope to fill.
"The beauty of an SROI report is that it spurs public engagement and forces the developer to be more transparent," society chairman Samuel Hung Ka-yiu said.
The team asked 1,007 people if they were willing to sacrifice time and money to protect the Chinese white dolphins. While 30 per cent chose to pay nothing, the rest indicated willingness to give HK$253 a year on average over 10 years. About 86 per cent were willing to spend 10 to 40 minutes more on the hour-long ferry ride to Macau that now cuts through dolphin waters. The results translate into HK$18.6 million in social costs. The net loss of tourism revenue is HK$17.5 billion.