The environmental impact of aviation is increasing faster than predicted by many industry and government estimates, according to an unpublished study undertaken last year by an influential group of aviation experts.

The report, Trends in Global Noise and Emissions From Commercial Aviation for 2000 through 2025, warns total emissions from the global aviation sector will soar from 572 million tonnes in 2000 to between 1.2 billion and 1.4 billion tonnes by 2025.

The projections, which are based on official government figures on the number of flights and authoritative emission modelling techniques, are broadly in line with the worst case scenario put forward by the UN's Intergovernmental Panel on Climate Change (IPCC), but are some 20 per cent higher than the best case scenario, which had been widely endorsed by many within the aviation industry.

The study also found that industry projections for the numbers of people affected by aircraft noise and levels of NOx pollution around airports have been underestimated, warning that by 2025 30.3 million people will be affected by aircraft noise and that NOx pollution will more than double to 6.1 million tonnes.

The report was compiled by representatives from US Department of Transport, European air traffic control agency Eurocontrol, Manchester Metropolitan University and technology company QinetiQ, and was submitted at the Air Traffic Management R&D seminar in Barcelona last year hosted by Eurocontrol and the US Federal Aviation Authority.

However, the report's authors were subsequently told that it would not be published and the document was removed from the conference website.

Jeff Gazzard, a board member for the Aviation Environment Federation, the lobby group which uncovered the report, said that the study had been "suppressed", a charge representatives of the aviation industry strenuously denied.

A spokesman for the IATA insisted that far from being "suppressed" the document had instead formed part of the the ICAO 2007 environment report, which has been published on line since Summer 2007. He added that the study had failed to take account of potential improvements in technology and air traffic management designed to cut aviation emissions.

His stance was supported by a spokeswoman for Eurocontrol who argued that the failure of the report to account for such improvements meant that "to present the figures put forward in the paper or the report as a realistic scenario is therefore misleading".

However, Gazzard insisted that the projections in the report appeared largely accurate, arguing that any significant improvements in the fuel efficiency of aircraft are likely to take decades to filter through due to the slow rate of replacement of many fleets. "The IATA [International Air Transport Association] said recently that the industry would continue to grow by between five and six per cent a year and deliver efficiency improvements of between one and two per cent," he said. "Well, if you extrapolate out those figures you are looking at emissions of between 1.2 billion and 1.4 billion tonnes a year by 2025, just as this report warns."

Should emissions reach such levels, any reduction in emissions attained by other areas of the economy will be negated, according to Gazzard. "If you accept that CO2 emitted at high altitudes has double the warming effect of that released at low altitudes, which is entirely legitimate for this type of study, then by 2025 annual aviation emissions will already account for half the total yearly emissions allowed by the entire economy in 2050," he warned.

Gazzard argued there was an onus on the aviation industry to be more realistic in its emission projections in order to ensure policymakers are fully aware of the scale of threat posed by aircraft emissions.