UN climate chief Christiana Figueres on Thursday urged the air transport industry to press on with curbs on emissions, underlining that it held "critical keys" to tackling global warming.

Aviation produces an estimated two percent of global emissions from human activity which "if left unchecked, will have further impacts on climate change," Figueres told an industry conference on aviation and the environment.

"The world will continue to need a stong aviation industry but the high flying plane must also be a symbol of pro-active action to address climate change," she added.

"Your sector has been proactive and I welcome that ... but we face major challenges and the aviation sector holds some critical keys."

Figueres, the executive secretary of the UN Framework Convention on Climate Change (UNFCCC), delivered her speech in a video message to the two-day gathering in Geneva.

Over the past three years, airlines under the wing of the International Air Transport Association (IATA), backed by the aerospace industry and airports have set targets for cuts in carbon emissions.

They include 1.5 percent-a-year increases in fuel efficiency by 2020, carbon neutral growth thereafter and a 50-percent cut in carbon emissions by 2050 compared to 1990 levels.

Cuts are being sought through more efficient modern aircraft, better flight management and air traffic control and improvements in infrastructure, as well as the ongoing development of biofuels.

Industry executives however warned that they needed a global and coordinated approach from governments to issues such as aviation emissions, flight paths and to stimulate the nascent biofuels industry.

Paul Steele, head of the Air Transport Action Group, a joint lobby for airlines, airports and aircraft makers, said 12,000 new aircraft would be needed at a cost of 1.3 trillion dollars to meet the 2020 target.

Carbon neutral growth "is probably the most crucial target and probably the most difficult one, and it's certainly politically the most contentious one."

"What we're seing emerge is... a fragmented approach," he complained.

The industry is pressing the 190-nation International Civil Aviation Organisation to agree on a global framework on emissions at its assembly starting on September 28, before aviation and shipping are scrutinised at the UN climate confrence in Cancun in December.