Of all the possible sources of renewable energy, wind farms have provoked some of the strongest resistance. Objectors point to a variety of concerns, from the risk posed to migratory birds to the chance that the spinning blades could fling ice in all directions during winter. But most of all, it seems, people just don't want the towering turbines to spoil the views from their back gardens.

So proponents of wind power were thrilled to learn in December that the current design for what is to be the world's tallest building — to be erected at the site of the terrorist attacks on 11 September 2001 in New York — calls for a massive wind farm in its upper storeys. When completed, the Freedom Tower and its turbines will be visible to millions (see page 12).

Provided, that is, that the wind turbines are ever installed. They were the brainchild of the architects Skidmore, Owings & Merrill. But people who build wind turbines for a living say they doubt whether the architects consulted wind engineers before floating the proposal. They say the structural challenges involved in damping vibrations and noise are too great to be cost-effective. One told Nature he thought the proposal was a joke. Another said he didn't believe that the turbines would ever be built. Skidmore, Owings & Merrill declined Nature's request for a response to the criticism.

Nevertheless, several optimistic companies have submitted proposals. One says it can make the job cost-effective with a turbine that spins on a vertical axis, rather than the usual propeller-like blades that spin on a horizontal axis. This would be good news, but the fact remains that vertical-turbine technology lags far behind and has not yet been used in any successful commercial installation.

Much more is at stake here than just an engineering dispute over what is possible. The amount of electricity involved is small compared with New York's voracious appetite, but the symbolism is huge. Wind power, whether urban or rural, could help ease us into our inevitable oil-free future. Yet a failure on the scale and visibility of the Freedom Tower could dampen enthusiasm for this much-needed renewable resource far more than a few dead birds could. Let's hope the optimists have it right.