The big President’s Day rally on the National Mall is more than a Keystone pipeline protest. It’s a statement of principle for climate action.

After a year of unprecedented destruction due to weather extremes, the climate fight is no longer just about impacts in the future. It’s about physical and moral consequences, now. And Keystone isn’t simply a pipeline in the sand for the swelling national climate movement. It’s a moral referendum on our willingness to do the simplest thing we must do to avert catastrophic climate disruption: Stop making it worse.

Specifically and categorically, we must cease making large, long-term capital investments in new fossil fuel infrastructure that “locks in” dangerous emission levels for many decades. Keystone is a both a conspicuous example of that kind of investment and a powerful symbol for the whole damned category.

A message from The Wilderness Society:

The Senate is voting on a bill this week that would allow drilling in the Arctic Refuge. Help stop it!

It’s true that stopping a single pipeline — even one as huge and odious as Keystone — will not literally “solve” climate disruption. No single action will do that, any more than refusing to sit on the back of a single bus literally ended segregation. The question — for Keystone protestors as it was for Rosa Parks — is whether the action captures and communicates a principle powerful enough to inspire and sustain an irresistible movement for sweeping social change.

Stopping Keystone nails the core principle for climate responsibility, by preventing investments that make climate disruption irrevocably worse. Again, it’s not just that burning tar-sands oil produces a lot of emissions; it’s that long-term capital investments like Keystone (and coal plants, and coal export facilities) “lock in” those dangerous emissions for decades and make catastrophic climate disruption inevitable.

Now, if you are a fossil fuel company, “locking in dangerous emissions” means locking in profits. It is your business strategy, precisely. For the rest of us, it’s a one-way, non-refundable ticket to centuries of hell and high water. We must not buy that ticket.

This is the Keystone Principle. It emerges from multiple lines of scientific and economic research, most notably the International Energy Agency’s 2012 World Energy Outlook, which starkly warned that the chance to avert catastrophic climate disruption would be “lost forever” without an immediate shift away from fossil fuel infrastructure investment.

But it doesn’t take a supercomputer to confirm that the Keystone Principle is basic common sense. It’s step one for getting out of a hole: Stop digging. A comprehensive strategy for global climate solutions called “Design to Win” put the point succinctly: “First, don’t lose.” The choice is clear and binary: Do it and we’re toast. So don’t.

In contrast, the many things we must do to advance positive climate solutions — clean energy, more efficient cars and buildings, better transportation choices — are full of grey areas. Implementing them is inherently slow, incremental, and subject to tradeoffs based on economic and other factors. Should new fuel economy standards make cars 80 percent more efficient or 90 percent? Over what period of time? The answers are judgment calls, not moral absolutes. But when it comes to stopping Keystone and other fossil fuel infrastructure investments, the choice is stark, clear.

“Climate solutions” are millions of Yeses and many shades of green, over a long period of time. But they also require a few bright red Nos, right now. These Nos are, you might say, the “keystone” for responding to the climate crisis, as in “something on which associated things [like, say, all efforts to avert catastrophic climate disruption] depend.” No amount of clean energy investment will stave off disaster unless we stop feeding the fossil fuel beast with capital now.

Most importantly, as we enter the era of climate consequences, the Keystone Principle has moral power. Many lives were lost, and millions disrupted, by superstorm Sandy. Most of the counties in America were declared disaster areas last year due to drought. Last month, parents in Australia sheltered their children from “tornadoes of fire” by putting them in the ocean. This is what climate disruption looks like.

Now that the faces of the victims are regular features of the daily news, what will we say to them? And what will we say to our children — the prospective victims of still-preventable disasters? Defying the Keystone Principle is like saying “Sorry, you’re out of luck. We will use our laws, our time, and our money to make it irretrievably worse.”

President Obama has begun to carefully edge away from the moral bankruptcy of this position. As he said in his inaugural address: “We will respond to the threat of climate change, knowing that the failure to do so would betray our children and future generations.”

But no one will believe him, or us, until we stop making it worse. That’s what Keystone is about. It’s not just a pipeline. It’s a principle.