Judging by the way we commonly talk about climate change, we don't yet grasp the ultimate stakes in the emergency that will dominate the 21st century. Headlines and editorials warn about the declining "health" of the Earth or declare that the damage humans are doing amounts to "treason against the planet." Since the first Earth Day almost 40 years ago, our worries have focused on "the fate of the Earth."

If I had one thing to impart to our leaders and opinion-makers, it would be this: Start worrying instead about the fate of human civilization. The Earth will survive the assault of the modern era. The urgent question is whether the Earth will remain a place that can support a complex, interconnected global civilization such as our own.

Scientists over the past 40 years have gained a revolutionary new understanding of Earth's long, eventful history, challenging common notions about the planet and modern civilization. The Earth, it turns out, is not at all fragile; it has survived an ancient oxygen pollution crisis, asteroid hits and other shattering catastrophes. The current crisis does threaten with extinction a great many of the plants and animals now alive; such a loss would extinguish earthly wonders, unhinge natural systems and undermine human well-being in countless ways.

On a human time scale, this would be a full-blown catastrophe. But odds are Earth's great collaborative, dynamic, interactive system now known as Gaia will endure, and, given some tens of millions of years, it will seize the creative possibilities presented by disaster, transforming bitter lemons into sweet lemonade. Indeed, one of these past cataclysms made our kind of oxygen-breathing, multicellular life possible. As the eminent microbiologist, Lynn Margulis, put it: "Gaia is a tough bitch."

Our powerful civilization, on the other hand, is profoundly vulnerable. The cores of ice drilled from the ice sheets on Greenland and Antarctica tell us we live at a truly extraordinary time within the Earth's volatile climate history. For the past million years, the Earth has swung between ice ages and brief, warmer interglacial periods that often last no more than 6,000 years. Because of the current shape of the Earth's orbit, our own interglacial period has lasted far longer, almost 12,000 years, blessing us with the long summer, which has been critical to recent human history. This extended tranquil period gave humans the conditions and the time needed to develop agriculture and build complex civilization. The world as we know it has been possible only because of a rare interlude of climatic grace.

Without interference, the long summer might have lasted another 10,000 to 20,000 years. But our dangerous disruption of the Earth system, most notably by our burning of coal and oil, is bringing it to an end. This confronts us with great uncertainty and many dangers, as the world's leading climate scientists warned recently, including a growing risk of "abrupt or irreversible climatic shifts."

Farmers in the Northeast already are experiencing wetter conditions and more intense rains, while other regions such as California and the Southwest face the danger of long-term drought. Energy Secretary Steven Chu warned that current trends are ominous: "We're looking at a scenario where there's no more agriculture in California."

It is possible that Earth's climate could "flicker" for several decades as it has in past transitions, swinging wildly between one climate state and another before settling down. Even without abrupt shifts, there is the danger that the warming itself could trigger a return to much greater climatic variability.

Before the calm of the long summer, our ancestors endured a demanding climate marked by fluctuations from decade to decade that were 10 times greater than current climate extremes. Such conditions, typical of the Earth's climate over most of the past 800,000 years, would be devastating to agriculture and civilized existence. We could lose far more than coastal cities and cultural treasures to extreme weather and rising seas; the ultimate stakes in this planetary gamble is the stable climate that has made civilization possible.

This is first and foremost a crisis for humans. Once we understand that clearly, perhaps we'll finally get serious about doing whatever is necessary to avoid the worst.

A version of this commentary first appeared at DailyClimate.org.