Whenever I hear the word “cliff,” I am reminded of something that President Obama’s science adviser, John Holdren, used to say about how we need to respond to climate change because no one can predict when it might take a disruptive, nonlinear turn. “We are driving toward a cliff in a fog,” said Holdren about the climate, and that’s always a good time “to start tapping on the brakes.” Indeed, when you think about how much financial debt we’ve built up in the market and how much carbon debt we’ve built up in the atmosphere, the wisest thing we could do as a country today is to start tapping on the brakes by both emitting less carbon to bend the emissions curve down and racking up less debt to bend our debt-to-G.D.P. curve down. Unfortunately, we are still doing neither.

Indeed, we are actually taunting the two most powerful and merciless forces on the planet, the market and Mother Nature, at the same time. We’re essentially saying to both of them: “Hey, what’ve you got, baby? No interest rate rises? A little bitty temperature increase? That’s all you’ve got?” I just hope we get our act together before the market and Mother Nature each show us what they’ve got.

Let’s look at the huge carbon and financial deficits we’re amassing. For thousands of years up to the dawn of the industrial age 200 years ago, the Earth’s atmosphere contained 280 parts per million of the heat-trapping greenhouse gas carbon dioxide. Today, that number is nearly 400 p.p.m., with 450 p.p.m. routinely cited as the tipping point where we create the conditions for out-of-control acceleration. Melting the permafrost in Alaska, Canada and Siberia, for example, would release massive amounts of carbon that would further increase global warming. Permafrost is packed with CO2 and frozen methane, which is 25 times more potent a greenhouse gas than CO2. “If the tundra continues melting,” says Hal Harvey, the chief executive of Energy Innovation, “we could basically release the equivalent of all the carbon that all humanity has emitted from the start of history to now.” That would really send temperatures soaring, ice melting and sea levels rising.

We’re on a similar trajectory with our debt. Mounting deficits have driven America’s debt-to-G.D.P. ratio from 36.2 percent in 2007 to 72.8 percent today. In their widely hailed book on credit crises, “This Time Is Different,” the economists Carmen Reinhart and Kenneth Rogoff argue that countries that allow their debt-to-G.D.P. ratios to exceed 90 percent experience slower growth and greater instability — much like hitting a climate tipping point. Indeed, they note, those who would point to low interest rates today as some kind of “all-clear” for more debt “should remember that market interest rates can change like the weather.”

There is another striking parallel. At some point, when we allow so much carbon to build up in the atmosphere, our mightiest efforts to cut emissions through energy efficiency, conservation and new technologies will only enable us to stay in place. They won’t be able bend the curve downward anymore. And 450 p.p.m. is not a place we want to get stuck. And, at some point, the debt will get so large that big tax increases and spending cuts will simply go to pay interest. We also won’t be able to bend that curve anymore, and spending on infrastructure, education and the poor will vanish.

I am struck by how many liberals insist on reducing carbon emissions immediately, but, on the deficit, say there is no urgency because no interest rates rises are in sight. And I am struck by how many conservatives insist we must reduce the deficit immediately, but, on climate, say there is no urgency because, so far, temperature rise has been slight. (Although 2012 was the hottest year on record in the continental U.S.) One reason interest rates are so low is that they are being suppressed by the Federal Reserve’s quantitative easing. That won’t last. As for the climate, well, “Mother Nature doesn’t do quantitative easing,” said Harvey. Beware of nonlinear moves in both.

We can’t go off coal overnight, and we can’t go into recession by cutting spending overnight, but we need to start tapping on the brakes in both realms by agreeing on spending cuts, tax increases and new investments that would be phased in as the economy improves, as well as higher efficiency standards for power plants, buildings, vehicles and appliances that would be phased in, too.

A carbon tax would reinforce and make both strategies easier. According to a September 2012 study by the Congressional Research Service, a small carbon tax of $20 per ton — escalating by 5.6 percent annually — could cut the projected 10-year deficit by roughly 50 percent (from $2.3 trillion down to $1.1 trillion).

What would you rather do to help solve our fiscal problem: Give up your home mortgage deduction and wait two more years for Social Security and Medicare, or pay a little extra for gasoline and electricity? These will be our choices. I’d rather pay the little carbon tax, especially since it would clean up the air for our kids, drive innovation and make us less dependent on the most unstable region in the world: the Middle East.
How could a carbon tax not be on the table today?