Technology, taxation, and rationing are all being eyed as possible solutions.
For the hundreds of climate-change activists who've camped out by Heathrow Airport this week, there is just one way to reduce aircrafts' carbon footprint: stop flying.
"Aviation is a luxury we can live without," says a protester named Merrick. Air travel, he says, is booming, multiplying greenhouse gases just as the climate-change imperative starts to bite. "It has to be scaled right back."
As protesters plan an unspecified action this Sunday, aircraft engineers, scientists, and climate experts around the world are urgently assessing if technology, taxation, and rationing – or a combination of all three – is required to stop aircraft from overbalancing the climate-change equation.
The statistics look ominous. Aviation currently contributes about 3 percent of global carbon emissions, but air travel is growing at some 5 percent a year, meaning numbers of air passenger kilometers will triple by 2030. Boeing estimates that aircraft numbers will double to more than 30,000 in little more than a decade.
Added to this is the complication that aircraft do not just give off carbon dioxide but nitrous oxide, thought to have at least double the impact of CO2, and condensation trails, which also may contribute to global warming.
For some, including President Bush's senior environmental adviser James Connaughton, the answer lies chiefly with technology. Aircraft manufacturers are constantly improving design of bodywork and engines, deriving greater fuel efficiency that reduces carbon emissions.
A British study group dubbed Omega (Opportunities for Meeting the Environmental Challenge of Growth in Aviation) is looking at a range of technological and other factors, including aircraft design, sustainable fuels, and open rotor-propelled aircraft that reduce fuel burn, to assess how they could mitigate aircraft pollution.
Boeing last month unveiled the 787 Dreamliner, which it says will use 20 percent less fuel than similar-sized aircraft. The UN International Panel on Climate Change says perennial improvements have made planes 70 percent more efficient than they were 40 years ago. Another 40-50 percent improvement can be expected over the next 30 years.
The problem, climate experts say, is that current projections indicate that air travel is set to grow 400 percent in the same time period.