In December I found myself sliding into a state of extreme unwillingness to take on new projects, to continue work on those in hand, to write, or do much of anything else, really, at work or at home. I found myself prodded awake in the night by worries about global warming, the tides of war and migration, the ramifications of random, dismal environmental facts come upon during the course of a day’s work, or of social justice problems encountered in the news and on the streets of Chicago; about any of which I can do very little to help. There were too many meetings with environmental groups, and no time for walks. I could not look at a tree without wondering how its species would fare in coming, climate disrupted years. I had reached a state of incipient burnout.

Thus, for a few weeks–a month and more, actually–after the solstice, I went into a state of semi-retreat. I did this by allowing myself to hope that COP21 would help bend the climate curve, and by pretending that our ongoing environmental catastrophe, of which climate change, is, after all, only a pernicious, deadly symptom, isn’t happening. I also attempted to pay less attention to the ever increasing spate of bad news, from war, to race relations, to migration, to the grim presidential race—and on and on and on, much of which is at least partly related to said catastrophe, with some industrial civilizational collapse, resource depletion and overpopulation thrown in.

Read more: Ecological Gardening

Life depends on it. Bill McKibben on the big changes we’ve already made in remarkably short order.

Physics can impose a bracing clarity on the normally murky world of politics. It can make things simple. Not easy, but simple.

Most of the time, public policy is a series of trade-offs: higher taxes or fewer services, more regulation or more freedom of action. We attempt to balance our preferences: for having a beer after work, and for sober drivers. We meet somewhere in the middle, compromise, trade off. We tend to think we’re doing it right when everyone’s a little unhappy.

But when it comes to climate change, the essential problem is not one group’s preferences against another’s. It’s not—at bottom—industry versus environmentalists or Republicans against Democrats. It’s people against physics, which means that compromise and trade-­off don’t work. Lobbying physics is useless; it just keeps on doing what it does.

So here are the numbers: We have to keep 80 percent of the fossil-fuel reserves that we know about underground. If we don’t—if we dig up the coal and oil and gas and burn them—we will overwhelm the planet’s physical systems, heating the Earth far past the red lines drawn by scientists and governments. It’s not “we should do this,” or “we’d be wise to do this.” Instead it’s simpler: “We have to do this.”

And we can do this. Five years ago, “keeping it in the ground” was a new idea. When environmentalists talked about climate policy, it was almost always in terms of reducing demand. On the individual level: Change your light bulb. On the government level: Put a price on carbon. These are excellent ideas, and they’re making slow but steady progress (more slowly in the United States than elsewhere, but that’s par for the course). Given enough time, they’d bring down carbon emissions gradually but powerfully.

Time, however, is precisely what we don’t have. We pushed through the 400 parts per million level of CO2 in the atmosphere last spring; 2015 was the hottest year in recorded history, smashing the record set in … 2014. So we have to attack this problem from both ends, going after supply as well as demand. We have to leave fossil fuel in the ground.

Read more: Yes Magazine