Here’s what American exceptionalism means now: on a per-capita basis, we either lead or come close to leading the world in consumption of resources, production of pollutants and a profound unwillingness to do anything about it. We may look back upon this year as the one in which climate change began to wreak serious havoc, yet we hear almost no conversation about changing policy or behavior. President Obama has done nicely in raising fuel averages for automobiles, but he came into office promising much more, and Mitt Romney promises even less. (There was a time he supported cap and trade.)

It has been well over 100 years since the phenomenon called the greenhouse effect was identified, 24 years since the steamy summer of ‘88, when many of us first took notice, and, incredibly, 15 years since the Kyoto Protocol. That agreement stipulated that signatories would annually reduce their emissions of greenhouse gases and was ratified (and even acted upon) by almost every country in the world, including every industrialized nation but one. That would be the United States. Now that’s exceptionalism. (Bill Clinton signed Kyoto; George W. Bush, despite an election pledge, repudiated it.)

The climate has changed, and the only remaining questions may well be: a) how bad will things get, and b) how long will it be before we wake up to it. The only sane people who don’t see this as a problem are those whose profitability depends on the status quo, people of money and power like Romney (“we don’t know what’s causing climate change”), most of his party, and Rex Tillerson, the Exxon chairman, who called the effects of climate change “manageable.”

Which I suppose they are, as long as you’re wealthy and able to move around at will. But it’s not manageable to the corn farmers losing their crops (many are just chopping them down), the ranchers selling off their cattle, the thousands of people in Colorado burned out of their homes in fires caused by the worst drought since 1956 or those who will lose their homes or jobs to fire, flood, drought or whatever in coming years. How will they “manage”?

All of this is the tip of the iceberg, and the iceberg is, of course, melting. As Bill McKibben points out in a piece to be published in Rolling Stone on Friday, not only was May the warmest on record for the Northern Hemisphere, not only was it “the 327th consecutive month in which the temperature of the entire globe exceeded the 20th-century average,” but it was also followed by a June in which some 3,200 heat records were broken in the United States.

The first page alone of the Rolling Stone article will scare the pants off you, but the chorus needs to grow bigger, louder and stronger. That’s why the forthcoming book (due July 24) from Climate Central, “Global Weirdness,” is so welcome. “Global Weirdness,” which explains climate change in simple, easy-to-understand language and ultrashort chapters, is intentionally calm because, says Michael Lemonick, one of the authors: “Some people respond well to ‘Big trouble is coming and we must do something immediately,’ but others are overwhelmed and just turn off. We believe that if you look at all the available evidence it’s clear we’re pushing the earth into a regime where it hasn’t been before, and the effects could well be disastrous.”

The time to avoid calamitous effects has likely passed. This doesn’t mean the situation is hopeless, but the longer we wait to curb emissions, the worse and longer-lasting the effects. Climate Central’s projections show that the biggest cities in Florida, and a great deal of the Northeast coastline (including New York City), will be underwater by 2100, when almost everyone now alive will have “managed” to leave the scene. Of course, the calamities won’t be limited to North America, nor is 2100 some magical expiration date; the end isn’t in sight.

Only reducing carbon emissions can keep matters from becoming worse. Thus the argument for a tax on carbon has never been stronger, but neither has the power of the energy companies to compel legislative paralysis on this issue. The way to a carbon tax is through Congress and the White House, but installing a responsible Congress means campaign-finance reform, another challenge of which Americans are aware but clueless about how to address. But feelings of helplessness are practically un-American: we have the opportunity to demand principled and independent leadership, if we will only try.

It was just about a year ago that we saw the beginnings of what is now called the Occupy movement. And although income inequality has hardly been “solved,” it’s a bigger part of the conversation now, and that may well spell Romney’s downfall. A similar movement — one that, as McKibben told me, “identifies the fossil fuel industry as the real enemy in the climate fight, which is ultimately a moral battle” — could possibly get things moving. If we can force our next president to turn his attention to a problem that may well dwarf the economy in scale, perhaps American exceptionalism will come to mean leadership in the right direction.