“Injustice anywhere is a threat to justice everywhere,” wrote Martin Luther King Jr. from a Birmingham jail on April 16, 1963. “We are caught in an inescapable network of mutuality, tied in a single garment of destiny.”

The Atlanta-based King was explaining why he was in prison for nonviolent demonstrations so far from home, responding to a critical public statement by eight Southern white religious leaders.

His words are timeless and universal, in part because King was a master of language, but primarily because he viewed civil rights through a moral lens. The greater the moral crisis, the more his words apply.

The greatest moral crisis of our time is the threat posed to billions — and generations yet unborn — from unrestricted carbon pollution. Now more than ever, we are “tied in a single garment of destiny,” cloaked as a species in a protective climate that we are in the process of unraveling.

Many have criticized the demonstrations against the Keystone XL pipeline, which would open a major spigot to the Canadian tar sands, as unwarranted and untimely — unwarranted given our broad dependence on fossil fuels and untimely because of our struggling economy. We disagree.

We think there has been far too little direct action, given the staggering scale of the threat. As the International Energy Agency has explained, we must leave the vast majority of fossil fuels in the ground if we are to preserve a livable climate and avoid levels of warming that “even school children know” will be catastrophic for us all. The tar sands would be near the top of any list of the largest, dirtiest pools of carbon that must be forsaken for the sake of humanity.

King explained in his letter: “In any nonviolent campaign, there are four basic steps: collection of the facts to determine whether injustices exist; negotiation; self purification; and direct action.”

Has there ever been a problem where more facts from more unimpeachable sources have been collected and ignored than climate change? Every major scientific body and international group has taken to begging and pleading for action.

Last fall, the World Bank — no bastion of eco-consciousness — issued a report aimed to “shock us into action.” It warned “we’re on track for a 4-degree Celsius warmer world marked by extreme heat-waves, declining global food stocks, loss of ecosystems and biodiversity and life-threatening sea level rise.”

If we don’t act now, then, within decades, a large fraction of the world’s 9 billion people will find themselves living in places whose once stable climate simply now can’t sustain them — either because it is too hot or arid, the land is no longer arable, their glacially fed rivers are drying up or the seas are rising too fast.

The overwhelming majority of those suffering the most — in this country and especially abroad — will be people who contributed little or nothing whatsoever to the problem.

This would be the greatest injustice in human history, irreversible on a time scale of centuries.

Has there ever been a problem subject to more failed negotiations? The international climate talks have been going on for a quarter century, full of sound and fury, but thwarted in large part by a U.S. Senate that itself talks to death every serious climate bill.

By “self-purification,” King meant preparing the group of protestors for the rigors and trials of nonviolent demonstration. But it’s his thoughts on another group that strike nearest now: “I have been gravely disappointed with the white moderate,” he wrote in words that apply to today’s moderate, status quo intelligentsia of every color. “Shallow understanding from people of good will is more frustrating than absolute misunderstanding from people of ill will. Lukewarm acceptance is much more bewildering than outright rejection.”

We understand why the fossil fuel industry works to block Congressional inaction and funds what has become the most effective disinformation campaign in history. Those who claim to accept climate science, but feel no urgency to act bewilder us.

As King put it: “We will have to repent in this generation not merely for the vitriolic words and actions of the bad people but for the appalling silence of the good people.”

Especially relevant are King’s words about time: “All that is said here grows out of a tragic misconception of time. It is the strangely irrational notion that there is something in the very flow of time that will inevitably cure all ills.”

As King explains, time “can be used either destructively or constructively. I am coming to feel that the people of ill will have used time much more effectively than the people of good will.” We feel the same.

Certainly nothing compares to the centuries of racial injustice King was impatient about. But each year brings an ever-worsening array of megadroughts and superstorms juiced by global warming like a baseball player on steroids. Each year brings higher emissions and ever more dire studies.

We know we’re fast approaching climatic tipping points — the loss of Arctic sea ice, the disintegration of the great ice sheets, the release of vast amounts of carbon from the permafrost, Dust-Bowlification of much of the world’s arable land — that are irreversible and catastrophic.

Even once-reticent climatologists are speaking out because, as Dr. Lonnie Thompson has written, “Virtually all of us are now convinced that global warming poses a clear and present danger to civilization.” Others, like James Hansen and Jason Box, have themselves joined direct action and been arrested for it.

It is past time for many more to speak out, and for many more to join direct action.

We end with King on the need to act now: “There comes a time when the cup of endurance runs over, and men are no longer willing to be plunged into the abyss of despair. I hope, sirs, you can understand our legitimate and unavoidable impatience.”

Van Jones is president of Rebuild the Dream and author of “Rebuild the Dream.” Joseph Romm runs ClimateProgress.org and is author of “Language Intelligence: Lessons on Persuasion from Jesus, Shakespeare, Lincoln, and Lady Gaga.”