There is no Planet B

Which is why we need a Plan B

What’s the fallback when global warming gets worse?

We humans as a species have been through this before. In fact, we've been through a lot worse than what's projected. Climatologists predict disaster if the global temperature rises 2 degrees Celsius above the present average. Yet between the last glacial maximum, around 20,000 years ago, and the present, the earth's average temperature has risen 7 degrees Celsius, and the human species has flourished—if anything, flourished too well, as evidenced by the effect we’re having on the climate and much else about the planet.

How did this flourishing happen, amid the dramatic climate change? Simple—we adapted to the changing circumstances. When ocean levels rose, we abandoned low-lying communities. We planted farms and built cities where glaciers had been. In areas where the rains stopped falling, we left whole cities behind.

The adjustments are easy to describe, but they were hard to accomplish. Indeed they must have been traumatic for the people who endured them. These people had no theories of climate to explain what was happening. They probably thought they had offended the gods. Perhaps they offered sacrifices to appease the deities and restore conditions to what they had been. When the conditions kept changing, they probably thought their gods had abandoned them.

We should hope we and our descendants don’t have to make similar adjustments.  In an ideal world, we’d take the hint of the last few decades and dramatically reduce the carbon dioxide we pour into the atmosphere. But our world is far from ideal, and to count on a global outbreak of virtue and good sense would be naive in the extreme. 

So we’d better plan for the worst. Our forebears can offer guidance. In the period after the Civil War, American settlers colonized the Great Plains. For a couple of decades they convinced themselves that the farming practices that had succeeded in the East would succeed in their new homes in the West. As it happened, those decades were unusually mild and wet by the historic standards of the Plains. When weather patterns regressed to the mean, the settlers were frozen and parched out. Today the Plains states still show the scars of the failed experiment: houses and barns fallen to ruin, schools and churches that haven't seen pupils or worshippers in a century.

Something similar happened to the ancestral Puebloan people of Chaco Canyon in New Mexico. A millennium ago they built a thriving culture characterized by cities, temples and trade connections with surrounding regions. Then the climate changed and they had to leave it all behind.

Three hundred miles southwest of Chaco Canyon lies Phoenix, the fifth largest city in the United States. The aptly named Valley of the Sun, the setting for Phoenix, was uninhabitable by large numbers of people before the construction of reservoirs, canals and pipelines to import water from a much wider area, and the introduction of electric-powered air-conditioning to make summers survivable. Phoenix has been getting hotter and thus more expensive to maintain. So far it has continued to grow, but there might very well come a time when people start deciding that the costs of summer in Phoenix don’t outweigh the benefits of winter. The city won’t become a ghost town overnight, but it could become a late-twenty-first century version of Detroit or Buffalo, which for different reasons lost population over decades and remain shadows of their mid-twentieth-century selves.

This is probably how Chaco depopulated. There’s no evidence of a catastrophic event—a massive earthquake, a horrible plague, a crushing defeat in war—that scattered the Chaco dwellers. Rather, life became gradually harder, and over time people decided to leave.

It goes without saying that abandoning Phoenix would be a bigger deal than leaving Chaco, if only in terms of the number of people involved. This is one reason for doing all we can to mitigate climate change.

But honesty should compel us to admit that our efforts might not do the trick. What do we do if they don't? 

Adjusting to climate change will be politically painful for Americans, but economically possible. We’re rich, and we can absorb the costs. Poorer countries will have it much harder. Low-lying Bangladesh has always been at risk of flooding; as ocean levels rise the risk increases. If large parts of Bangladesh become uninhabitable, Bangladeshis will seek higher ground in neighboring countries. They won’t be uniformly welcomed, and wars might ensue. In fact, it was a refugee-triggered war in 1971 that led to the creation of Bangladesh out of what had been East Pakistan.

Other conflicts will result from too little water rather than too much. Water is becoming scarce in parts of China, and the Chinese government has taken measures to seize more. New dams on the upper Mekong River are reducing what’s left for the countries downstream. Those countries complain, but against the regional superpower they don’t stand a chance. In resource wars, as in much else in international affairs, the powerful take what they will, and the weak have to settle for what's left.

Things could get really ugly. Again, Plan A must be to keep global warming to the minimum still possible—recognizing that the much of the warming effect of carbon-dioxide already emitted has yet to be felt.

But there has to be a Plan B, in the likely case Plan A falls short. In America, cities and states can be expected to struggle against the results of a changing climate. New York City will build storm surge barriers like those on the Thames River below London. Californians are already talking about taking water from the Mississippi and pumping it across the continental divide.

But there's a limit to what can be accomplished by geo-engineering. At some point we'll have to concede the lessons of our own past: that cities and smaller communities aren't necessarily forever. The Sunbelt might become the new Rust Belt as the shift of population from the northern part of the country to the southern reverses course. I was in North Dakota some years ago and met people who were quietly rooting for global warming. They loved their state but said they'd love it even more if it were a few degrees warmer.

We'll have less say over what happens in the world at large. It's hard to imagine American voters approving intervention in foreign water wars. Instead we'll have to look to diplomacy. This lacks the heady feeling that comes from swinging the biggest stick in world affairs. But we'd better get used to it. And none too soon. Our record in wars since 1945 hasn't been much to brag about. Besides, you can't get water from a stone, certainly not with weapons.

Which suggests that other countries ought to be developing Plan Bs of their own.