Faced with slow progress towards an international agreement to limit greenhousegas emissions, governments are taking
the initiative by passing their own climate laws. Mexico — plagued by a persistent drought but optimistic about its prospects for wind power — made one of the boldest commitments of any nation to limit climate change.
Although many countries have established domestic climate regulations, Mexico is only the second, after the United Kingdom, to make tough national targets legally binding.

A vast supply of energy is racing around the planet far above the surface. Erik Vance meets the engineers trying to bring the power of high-altitude wind down to earth.