n exuberant rite of spring” is how the New York Times described 22 April, 1970. In Manhattan, and across America, “huge, light-hearted throngs ambled down autoless streets.” Earth Day had been born, an outburst of protest – and revelry – that involved everyone from save-the-whales activists to opponents of new freeways. Denis Hayes, now 72, was the man tasked with organising it. “What we did was pull together an event that told all of those people, ‘You know you’ve really got something in common and this should be one big movement where we’re supportive of one another’.”It sparked, he tells me, the most profound change in American society since the New Deal. “We now have different kinds of buildings, different kinds of automobiles, different planes, different lighting, different land use. People are choosing to have diets for environmental reasons, choosing to have one child for environmental reasons.” And all that, he says, “didn’t come from political leadership at the top, it came from a bunch of demands down at the grassroots”.