Environmental campaigners have joined forces to oppose the £150 million expansion plans for Bristol International Airport.

A group including Dale Vince, the founder of the Stroud-based green power supplier Ecotricity, and Avon Wildlife Trust chief executive Steve Grainger, wrote a letter criticising the airport's growth plans.

Published in national newspaper The Guardian yesterday, it came on the last day of public consultation for the plans, which are being considered by North Somerset Council.

The letter said that while the Government has set a target for aviation emissions to be no higher in 2050 than they were in 2005, the airport intends to double its emissions in 10 years.

The airport claims passenger numbers will rise from six million a year in 2009 to 10 million by 2020.

Its submitted plans include multi-storey car parks, an expanded terminal and a new administration building for airport staff.

The letter said: "While advocates of BIA's plan claim that it will have significant economic benefits, it is clear that the number of jobs generated per million passengers is dropping due to the cost-cutting measures of airlines and airports.

"The airport also handles six to 10 times as many outbound tourists as inbound ones, causing a deficit to the UK economy of over £700m per year that far outweighs any jobs generated by the airport.

"Significantly, the South West tourist industry has in recent months seen a notable increase in visitor numbers at the same time as air passenger numbers have fallen.

"We believe that airport expansion is incompatible with reducing carbon emissions, that alternatives such as high-speed rail and video conferencing to replace business flights have been given insufficient consideration, and that the claimed economic benefits do not justify the damage that will be caused to the local environment by the physical impact of the expansion, as well as to the global environment by the increased emissions."

World Wildlife Fund aviation expert Peter Lockley, Christian Aid climate change campaigner Dr Alison Doig, Richard Archer of the Royal Society for the Protection of Birds, and Tim Baster, the executive director of the Climate Outreach and Information Network were the other signatories to the letter.

The airport issued a statement in response, which said: "Emissions from aircraft using Bristol International Airport account for less than one per cent of total UK aviation emissions.

"The planning application includes comprehensive measures to reduce direct emissions from the airport site, and from 2012 a mechanism will be in place to cap emissions from flights at 2005 levels, through the EU Emissions Trading Scheme. Airlines and passengers will have to reduce emissions or pay to offset growth.

"Sustainable Aviation (a coalition of airlines, airports, aerospace manufacturers and air navigation service providers working to address the future sustainability of the industry) projects that the sector's emissions can be brought back to 2000 levels by 2050 while still allowing the growing demand for air travel to be met.

"The work of Sustainable Aviation demonstrates that Bristol International Airport's development is consistent with plans for transition to a low carbon economy."