(Recasts with environmental impact, more details on airports)

By Robert Evans

GENEVA, July 18 (Reuters) - World international and domestic airports handled a record 4.4 billion passengers in 2006, an increase of 4.8 percent from the previous year, the global airports organisation ACI reported on Wednesday.

ACI, the Geneva-based Airports Council International, said the 1,640 airports operated by its members in 178 countries also processed nearly 86 million tonnes of cargo last year -- up 3.6 percent on 2005, reflecting booming world trade.

"The statistics tell a great story -- growth and stability," ACI Director General Robert J. Aaranson said in a statement issued with the figures. "Three-quarters of airports worldwide reported positive passenger growth."

Beijing airport saw the biggest rise in passenger traffic, up a whopping 19 percent from the previous year. Nearly 49 million travellers passed through the airport, making it the world's ninth busiest, up from 15th place in 2005.

Air industry analysts said the rapid growth was partly due to the Olympic Games, to be held in the Chinese capital next year, and also to mounting demand for international travel among China's 1.3 billion population.

The growth in air traffic has alarmed environmentalists, who say aircraft emissions and airport expansion are major contributors to global warming.

Some governments are taking measures, including imposing "green taxes" and other levies, to try to slow the increase in flight numbers -- largely sparked by the success of low-cost airlines around the globe.

EMISSIONS

But airlines argue only a small total of emissions are attributable to their industry, and that they are working to keep the levels low.

Earlier this year, the Geneva-based airlines body IATA -- the International Air Transport Association -- reported that passengers on its members' flights rose by 5.9 percent year-on-year in 2006, with freight traffic growing at 4.6 pct.

But the ACI figures are thought to offer a broader reflection of the state of the air travel and cargo industries since they cover hundreds of smaller airports handling purely domestic traffic as well as the big international hubs.

ACI data also includes travellers on low-cost carriers, most of which are not members of IATA.

Passenger numbers look set to rise further, with ACI reporting last month that numbers passing through its member airports in May were up five percent compared to May 2006.

Atlanta in the United States remained the world's busiest passenger hub last year with nearly 85 million travellers passing through, according to ACI.

It was followed by Chicago O'Hare with 77 million passengers and London's Heathrow with 67.4 million. All three -- and Tokyo's Haneda, in fourth place with nearly 66 million travellers -- were in the same position in 2005.

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