“Even if the United States deals with its carbon emission problem, the Chinese won’t. So what’s the point?”

“You can’t condemn the entire global South to abandon energy development, and you can’t provide enough with solar and wind. So what’s the point?”

“Besides, the whole enterprise of trying to achieve a future sufficiently carbon-free to deal with the most important problems is politically hopeless.”

These challenges are sometimes spoken, sometimes not, but they commonly and powerfully weaken efforts to deal with the climate crisis. Despite the well-funded bluster of disingenuous or, at best, delusional skeptics and deniers, a majority of Americans believe the climate is changing in worrying ways, and many (PDF) also believe that these changes pose a threat to current and future generations. But this belief has not yet translated into action at a scale adequate to the problem we face.

One reason for this is that once we recognize the magnitude of the effort that will be required to avert disaster, we all too often discover our vested interest in pessimism. After all, if the situation is hopeless, why act? But it’s time to challenge the structure of feeling that mires us in pessimism and inaction.

We appear to be on a trajectory well past the 2 degree Celsius rise in average global temperature long considered by scientists the maximum allowable to sustain life on Earth as we’ve known it. As Naomi Klein documents in her new book, “This Changes Everything,” many experts — from climate change scientists to the World Bank to the International Energy Agency — are warning of temperature increases of 4 or more degrees. Changes of this magnitude will likely result in widespread flooding, collapsing water systems, decreases in agricultural production, increases in disease, massive migrations and social strife.

“Only mass social movements can save us now,” Klein writes. I agree. We must build a truly broad movement — one that encompasses those who aren’t already convinced of the need to act — and alongside it a new politics capable of reasserting the power of democracy at all levels. Such a movement and politics must not only confront slow-to-act authorities with appropriate civil disobedience but also build the new economic institutions that will be necessary to a world weaning itself off its addiction to carbon and to growth.

But faced with such a tall order, many still ask (or secretly feel), Why bother? Or, more specifically, is it really possible to make more than a small nick in the dire warming trends?

The simple response to the reasonable doubts offered by friendly questioners — and to the reasonable (often unspoken) doubts of even committed activists — is this: Doing almost anything significant can help save human lives. This is an obvious point, perhaps, but one that too often is lost in the big debates about trends.