Airlines expect overall passenger numbers to double over the next two decades from the 4.3 billion who flew last year, with growth led by emerging markets such as Asia Pacific and the Middle East, the main global airline body said Thursday.

The projected surge in traffic could put further pressure on carriers to contribute to the fight against climate change and make progress towards a pledge to reach "net zero" carbon emissions by 2050.

Average annual passenger growth is expected to be 3.6 percent a year to 2043, compared with a forecast of 9.7 percent growth this year, the International Air Transport Association said in its latest update.

The Asia Pacific region would lead with average growth of 4.8 percent, propelled by countries like India (6.9 percent) and China (5.8 percent) but also Thailand and Vietnam (6.4 percent each), the IATA said.

Passenger growth in Africa and the Middle East would rise by 3.6 percent, while Latin American and the Caribbean would see a 2.9 percent increase.

The mature markets of North America and Europe would see growth of 1.7 percent and two percent, the association said.

Air transport currently accounts for less than three percent of global CO2 emissions, but is often in the firing line because it serves a minority of the world's population.

Airlines are mainly betting on increased production of sustainable aviation fuels produced from renewable sources, expected to provide 65 percent of the industry's "net zero" target for 2050.

But the technological challenges of producing such fuels at scale -- they currently provide just 0.53 percent of airlines' fuel consumption -- are likely to require huge investments.