Here’s a question whose answer might surprise you: what American songwriter penned the most-listened-to piece of environmental protest music of all time? Somebody with an acoustic guitar? John Denver?

The answer, almost certainly, is Marvin Gaye. “Mercy, Mercy Me (The Ecology)” appeared on What’s Going On, the album he released in May 1971, which went straight to the top of the charts, even though Motown boss Berry Gordy thought it was too political to sell. “I realized that I had to put my own fantasies behind me if I wanted to write songs that would reach the souls of people. I wanted them to take a look at what was happening in the world,” Gaye said later. The Vietnam War, protested in the album’s title song, was part of that story, and so was drug abuse–and so was “oil wasted on the oceans and upon our seas,” and “radiation in the ground and in the sky,” and “fish full of mercury.”

Where did all the blue sky go? Poison is the wind that blows From the north, east, south and sea

For a brief moment after the first Earth Day, it made perfect sense for the civil rights and environmental movements to be singing the same tune. Tragically, those movements soon diverged–diverged so far that some people still find it odd that activists like ourselves are working side by side again on issues like global warming and poverty. But it makes perfect sense–there is no threat to social justice greater than the breakdown of our earth’s physical systems, and no way to ease that threat without rearranging power, both in America and around the world.

Think for a minute about Hurricane Katrina: those high winds blew in a lot of truths. For one, we’ve amped up nature in a dangerous way: scientists now expect ever stronger storms to rake our shores. For another, poverty puts some people at far more risk than others. No one will ever forget those pictures of the Lower Ninth Ward when the levee broke, but in almost every city on earth the poorest people live in the equivalent of the Lower Ninth. It’s not that everyone won’t eventually be affected by climate change–plenty of middle-class white people lost their homes when the storm rampaged across Louisiana and Mississippi. But almost everywhere, rich people occupy higher ground, and the places that flood belong to those who can’t afford better. As the oceans rise throughout this century, those are the places that will turn wet and swampy first–substandard housing in the twenty-first century still means lead paint and asthma, but now it means you better cut a hole in the attic so you can get on the roof and wait for the helicopter.