Worsening droughts and biblical deluges are reducing food production and displacing millions of people. Record-high temperatures threaten to render areas of the Middle East and the Persian Gulf, North Africa and South Asia uninhabitable. Growing migrations of climate refugees are destabilizing nations. A sixth great extinction could extinguish half the species on earth.

[Al Gore answered questions about this essay on Twitter.]

Finally people are recognizing that the climate is changing, and the consequences are worsening much faster than most thought was possible. A record 72 percent of Americans polled say that the weather is growing more extreme. And yet every day we still emit more than 140 million tons of global warming pollution worldwide into the atmosphere, according to the Intergovernmental Panel on Climate Change. I often echo the point made by the climate scientist James Hansen: The accumulation of carbon dioxide, methane and other greenhouse gases — some of which will envelop the planet for hundreds and possibly thousands of years — is now trapping as much extra energy daily as 500,000 Hiroshima-class atomic bombs would release every 24 hours.

This is the crisis we face.

Now we need to ask ourselves: Are we really helpless and unwilling to respond to the gravest threat faced by civilization? Is it time, as some have begun to counsel, to despair, surrender and focus on “adapting” to the progressive loss of the conditions that have supported the flourishing of humanity? Are we really moral cowards, easily manipulated into lethargic complacency by the huge continuing effort to deceive us into ignoring what we see with our own eyes?

More damage and losses are inevitable, no matter what we do, because carbon dioxide remains for so long in the atmosphere. So we will have to do our best to adapt to unwelcome changes. But we still retain the ability to avoid truly catastrophic, civilization-ending consequences if we act quickly.