Global warming is now at the top of world concerns as scientists, politicians and everyday citizens ponder how to take immediate action against this slow-burning crisis. Yet British environmental activist Mark Lynas warns that all our success in conserving energy and using new fuels might be overwhelmed by a major greenhouse problem no one talks about: air travel.

“We could close every factory, lock away every car and turn off every light in the country,” he writes in New Statesman about Britain’s ambitious goals to cut carbon use, “but it won’t halt global warming if we carry on taking planes as often as we do.”

Lynas is referring to a report from the respected Tyndall Centre for Climate Change Research, which notes that if the UK’s annual 12 percent rise in air travel continues until 2050, the resulting increase in carbon dioxide (a leading cause of the greenhouse effect) would overwhelm progress in every other sector. Indeed, factoring in the projected growth of air travel, carbon emissions would have to be reduced to zero in manufacturing, ground transportation and private households to meet the British government’s 2050 green goals.

The story is the same in most other countries where the rise of budget airlines and globalizing businesses along with steady increases in tourism, immigration and people’s innate curiosity to see the world add up to more air passengers every year. Globally, air travel has increased 9 percent annually for the past 40 years, notes the French magazine Alternatives Ãƒâ€°conomiques.

I am, I confess, part of this problem. I never set foot on an airliner until age 23 but now I fly as many as 10 times a year for work and vacation. I think of myself as an environmentally conscious person — riding my bike for most trips around town and trying to recycle every last scrap in the house. Yet a look at the Atmosfair website (www.atmosfair.de) is sobering. The round-trip journey from my home in Minneapolis to the Ode office in the Netherlands (which I make several times a year) creates 4,560 kilograms (5 tons) of carbon dioxide.

While that sounds bad enough, Atmosfair (a joint project of German environmental groups and travel agencies) informs me that this is equivalent to the carbon output for the entire year for five people in India. As for my conscientious bike riding, well, one transatlantic round-trip flight contributes to global warming at twice the rate of driving a medium-sized car 12,000 kilometres (7,500 miles) a year. And the U.S. green group Natural Resources Defense Council notes carbon isn’t even the whole problem — nitrogen dioxide and water-vapour emissions from jetliners also worsen the greenhouse effect.

What are travellers, especially ones whose livelihoods depend on frequent flying, to do? Atmosfair and other websites will calculate the carbon output of your flying (or driving or home-energy use) and offer you the chance to offset these environmental costs with a donation to various projects that eliminate greenhouse gases. Al Gore, who constantly jets around the world to draw attention to the problem of global warming, told National Geographic Traveler magazine, “I buy offsets for every bit of it… My wife and I put money into a project in India that substitutes highly efficient solar units at $300 (240 euros) a pop for very dirty kerosene burners, which verifiably reduces a lot of C02.”

Climate Care, a British non-profit group, will offset the C02 of my U.S.-Netherlands trip for about $10 (8 euros). (Carbon calculation is still a new idea and there is some discrepancy on the price of my carbon “bill” between various websites; Climate Care came in the cheapest.) Its projects range from funding energy-conservation programs in Kazakhstan and South Africa to providing efficient cooking stoves in Honduras and Madagascar to backing reforestation initiatives in Uganda.

GreenSeat, a Rotterdam-based organization that also calculates carbon use and offers an offset program, is mounting an international petition campaign urging air carriers and travel agents to include a carbon-offsetting option as part of the standard ticketing procedure.

Meanwhile, KLM Royal Dutch Airlines is cutting emissions by boosting fuel efficiency. By running engines only when necessary, reducing the weight of onboard supplies and other strategic measures, it now averages 28 kilometres per litre (66 miles per gallon) of jet fuel per passenger, which is better than other airlines and even tops most motorists driving alone in their cars.

Alternatives Ãƒâ€°conomiques draws attention to the fact that jet fuel, unlike gasoline used in cars and buses, is not taxed anywhere in the world except the Netherlands. This means that other airlines have less incentive to improve fuel efficiency, and the price passengers pay for tickets does not reflect the environmental costs of flying.

Richard Branson, the brash entrepreneur behind Virgin Atlantic Airways and Virgin Rail, hopes to make air travel more sustainable by investing up to $1 billion U.S. (790 million euros) in what he calls, of course, Virgin Fuel. “It’ll be a clean fuel,” he told Business 2.0 magazine. “And if we’ve got it right, it could be a very important breakthrough. We think this fuel will work in cars and trucks and trains within a year. And we’re hoping that it might work in commercial jet engines within five years.” Branson’s Virgin Rail is also helping the situation with its new high-speed rail service between London and Manchester, which is luring many travelers out of plane seats, reports the Guardian.

While most people are not likely to stop flying, many in the environmental movement and even the travel industry question our overreliance on airplanes for trips that might more sensibly be made by other means of transportation. Mark Ellingham, founder of the popular Rough Guide travel handbooks, advocates that travellers “fly less often and stay longer.” In the vacation-strapped U.S., for instance, surveys show that people now take many long-weekend trips by air rather than going on one- or two-week holidays. That obviously creates far more greenhouse gases.

Ellingham advocates a Slow Travel movement, along the lines of the Slow Food movement, in which people savour their vacation experiences. “Travelling slower gives you a sense of place,” he told Sierra magazine. “Trains give you the chance to talk to people, to see a landscape unfold.”

The growing network of high-speed trains across Europe, Japan, Korea and Taiwan offer a vision of the future in which planes are used mainly for overseas and long-distance journeys, not short hops from Amsterdam to Paris, or Toronto to Montreal. The world’s high-speed rail leaders, France and Japan, are developing trains that travel 350 kilometres (220 miles) an hour. China has unveiled a maglev (magnetic levitation) train that reaches 500 kilometres (310 miles) an hour, whisking passengers between central Shanghai and PuDong airport 30 kilometres (20 miles) away. Construction is slated to begin soon on a 160-mile maglev line between Shanghai and Hangzhou.

Inspired by the success of the European and Asian trains, many other nations across the world, including Mexico, Brazil and Israel, are planning their own high-speed rail networks. Amtrak, the U.S. rail system, last year unveiled its Acela Express train, which hits a top speed of 150 miles (95 kilometres) per hour from Washington to New York to Boston.

Even the most time-pressed business travellers are finding that air travel is not so speedy these days when you figure in congested roads on the way to the airport and long lines at security gates. Flying has become increasingly inconvenient and uncomfortable in recent years so that now trains and buses, once regarded as old-fashioned and low class, seem luxurious in comparison. Airport hassles have spawned a new generation of comfortable, non-stop, intercity bus services such as Megabus and Lux Bus America in the U.S. — a development no one saw coming a few years ago.

A picture of green transportation for the future would let us choose — depending on our needs and the nature of our trips — between clean-fuel cars, comfortable buses, fast trains and planes using less fuel and creating fewer emissions — as well as the option for business travellers of not leaving home at all, and meeting instead by video conference.