Forty years ago, a team of scientists at the Massachusetts Institute of Technology raised the first warnings about possible “limits to growth.”

If human beings didn’t slow the expansion of the size of our populations and economies, they predicted, sometime in the ensuing 100 years we would more or less fall off a cliff: Our environmental troubles would get so bad that our economies, and our civilization, would start to become unworkable.

For most of the four decades since, that analysis has drawn scorn. People insisted that human beings could keep our enterprise expanding forever — increases in knowledge would always trump a degrading physical world. We’d never run out of, say, oil — or if we did, we’d invent some substitute and just carry on as before.

In the last few years, though, those scientists are starting to look more prescient. We do seem — in one realm after another — to be bumping up against limits.

For instance, per capita grain yields on this planet have been falling for many years now, because new technologies like genetically modified seeds have failed to increase yields — certainly not by enough to compensate for growing populations.

Now, the erratic weather that comes with climate change seems to be driving them down: This year, for instance, Russia suspended all grain exports after its record heat wave and drought.

Indeed, climate change may be the clearest sign of the trouble into which we’ve fallen. The steady rise of temperature (19 nations have set new all-time records this year, and Pakistan set the all-time Asian high at 53.89 degrees Celsius) has begun to lead to wholesale change. In the Arctic, for instance, massive melt continues apace. And across the planet, a warmer atmosphere is harboring more moisture, so deluge and flood have become constant companions: The trauma along the Indus River in Pakistan this August is only the largest example of many.

These changes, of course, hurt the poorest people first. They also diminish the possibilities for all who would come after us. And they are wreaking havoc on our biodiversity: As I write this, word comes that this summer’s heat has produced the worst coral bleaching on record, with many reefs now covered by the grayish slime that marks a dead underwater ecosystem.

Our only hope of checking this kind of damage is to get off fossil fuel, and to do so quickly.

Re-sourcing our energy use with renewable generation is technically possible — we know how to do things like solar and wind power. But it’s politically difficult because of the vast power of the fossil-fuel industry. Their business model depends on using the atmosphere as an open sewer to dump their waste into for free (which helps explain why they’re the most profitable business on earth). And their wealth affords them enormous political power, which they’ve deployed to delay action.

Overcoming that power will require building a movement. It’s what we’ve been trying to do at 350.org for three years now, with some success. We take our name from the limit that scientists have set on safe levels of carbon dioxide in the atmosphere, since above 350 parts per million — in the words of a NASA team — we can’t have a planet “similar to the one on which civilization developed and to which life is adapted.”

Pretty straightforward, that statement — and pretty scary when you know that everywhere around the world the atmosphere is currently 390 parts per million. We’re already way too high — that’s why the Arctic is melting and Russia is catching on fire and Pakistan is drowning.

So far we’ve had some success, organizing the two most widespread days of political action in the planet’s history, about any issue. Just recently, on Oct. 10, we coordinated 7,347 separate “work parties” in 188 countries, including every nation on earth but Equatorial Guinea and North Korea. We will keep fighting as hard as we can to build that movement — and to making sure it incorporates the fight for biodiversity protection.

We have no guarantees that we’ll win. The momentum of the heating we face is great, and the power of the industry is remarkable. We really are knocking up against powerful limits. But since there is no limit to the human spirit — to our compassion for each other and for the rest of Creation — we will keep fighting and keep hoping.

Bill McKibben is the founder of 350.org and a scholar in residence at Middlebury College in Middlebury, Vermont. His most recent book is “Eaarth: Making a Life on a Tough New Planet.”

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