A recent highly advanced computer using state of the art climate models for how an exo-civilization might evolve lead to some surprising results that civilizations tend to fall into one of three outcomes and that sometimes it did not matter what they did to try to change the consequences. You have to read pretty far down into the article, but a summery of what the models showed was that they saw three distinct kinds of civilizational histories. The first—and, alarmingly, most common—was what we called “the die-off,” which parallels what I have been thinking and saying for 40 years. As the civilization used energy, its numbers grew rapidly, but the use of the resource also pushed the planet away from the conditions the civilization grew up with. As the evolution of the civilization and planet continued, the population skyrocketed, blowing past the planet’s limits. The population, in other words, overshot the planet’s carrying capacity. Then came a big reduction in the civilization’s population until both the planet and the civilization reached a steady state. After that the population and the planet stopped changing. A sustainable planetary civilization was achieved, but at a high cost. In many of the models, we saw as much as 70 percent of the population perish before a steady state was reached. In reality, it’s not clear that a complex technological civilization like ours could survive such a catastrophe. In many ways we were seeing a kind of cosmic Easter Island play out. There may have been as many as 10,000 people living on Easter Island at the peak of its stone-head-making heyday. But by cutting down all the trees to roll the stone heads around, that civilization seems to have mucked up its ecosystem and sealed its own fate. When the Dutch arrived in 1722 only a few thousand folks, living greatly reduced lives, were left. The second kind of trajectory held the good news. We called it the “soft landing.” The population grew and the planet changed but together they made a smooth transition to new, balanced equilibrium. The civilization had changed the planet but without triggering a massive die-off. The final class of trajectory was the most worrisome: full-blown collapse. As in the die-off histories, the population blew up. But these planets just couldn’t handle the avalanche of the civilization’s impact. The host worlds were too sensitive to change, like a houseplant that withers when it’s moved. Conditions on these planets deteriorated so fast the civilization’s population nose-dived all the way to extinction. You might think switching from the high-impact energy source to the low-impact source would make things better. But for some trajectories, it didn’t matter. If the civilization used only the high-impact resource, the population reached a peak and then quickly dropped to zero. But if we allowed the civilization to switch to the low-impact energy resource, the collapse still happened in certain cases, even if it was delayed. The population would start to fall, then happily stabilize. But then, finally and suddenly, it rushed downward to extinction. The collapses that occurred even when the civilization did the smart thing demonstrated an essential point about the modeling process. Because the equations capture some of the real world’s complexity, they can surprise you. In some of the “delayed collapse” histories, the planet’s own internal machinery was the culprit. Push a planet too hard, and it won’t return to where it began. We know this can happen, even without a civilization present, because we see it on Venus. That world should be a kind of sister to our own. But long ago Venus’s greenhouse effect slipped into a runaway mode, driving its surface temperatures to a hellish 800 degrees Fahrenheit. Our models were showing, in generic terms, how a civilization could push a planet down the hill into a different kind of runaway through its own activity. Bottom line: instead of blaming man and calling for all kinds of draconian sacrifices to save the planet, these studies along with my own thinking for a very long time is that the real key to saving humanity and the planet lies less in how mankind lives and works, and much more so in how well we control our population. If we want to save the planet and mankind, I think we need to work towards cutting world population down by about 33% from what it is today. How Do Aliens Solve Climate Change?