Today's globalized economy largely rests on nineteenth- and twentieth-century revolutions in transport: humankind's ability to move goods and people around the planet by boat, train, car and plane. The global transportation network allows consumers to buy crisp New Zealand apples in London, fresh seafood in Oklahoma City and Chinese-manufactured goods everywhere.

Indeed, transportation is so integral to the global economy that 14% of the world's greenhouse-gas emissions come from that sector alone. And in the developing countries especially, that fraction is growing rapidly. Witness the explosion of private transport, which has always been a symbol of wealth: Beijing gets another 1,000 cars every day. Earlier this year, India's Tata Motors unveiled the world's cheapest car, a $2,500 bubble called the Nano. There is every reason to expect that car ownership will continue to increase towards that of the already developed nations, where between a third and half of the population owns a car.

This is why managing the greenhouse emissions from transportation has emerged as a major challenge in the twenty-first century. In a series of Special Reports (see http://tiny.cc/CyqtP), Nature looks at technologies that could help accomplish that goal. Some are relatively familiar, such as fuel cells running on hydrogen split from water via solar or wind power. Others have a definite back-to-the-future feel, such as kite-powered ships or steam-powered trains (see page 1036). All could have a significant impact.

Not so long ago most of these ideas would have been dismissed as pipe dreams. Today, if the soaring price of oil has a silver lining, it is that the push for alternative transportation technologies has become real and serious. Major research investments are being made by government, industry and venture capitalists. But oil prices are notoriously volatile; at this particular moment they seem to be declining. The challenge for policy-makers in every sector is to make sure those investments in future transportation are sustained for the long haul.