Of islanders, aliens, and frogs. A cosmic test for humanity. Part 2.

This is the 9th episode in a series recounting the history of measurements, data, and projections related to global climate change. If you’re just joining, you can catch up on the previous episodes:

• Episode 1: Beginnings (or two British scientists’ adventures with leaves and CO2 measurements)
• Episode 2: First measurement of anthropogenic global warming
• Episode 3: Our “large scale geophysical experiment” (1940-1960)
• Episode 4: Dave Keeling persists in a great idea
• Episode 5: Icy time capsules
• Episode 6: The “geologic eons of time”
• Episode 7: Our global thermometer since 1850
• Episode 8: Of islanders, aliens, and frogs. A cosmic test for humanity. Part 1.

Episode 9

“But where are they?” exclaimed the physicist, Enrico Fermi. He was sitting at lunch one summer day in 1950 at the Los Alamos National Laboratory with another physicist, Edward Teller, and two nuclear scientists, Emil Konopinski and Herbert York. Each of the scientists had contributed vitally to the creation of the atomic bombs that ended World War II. (Incidentally, 2 of the 4 scientists were American immigrants, 1 was a first-generation American, and 1 was part native American. You might say they perfectly represented the strength of the American melting pot.)

Improbably, Fermi was referring to space aliens.

Intrigued? If not, you’re brain dead! Everyone wonders about alien stuff!

It was the continuation of a conversation about the possibilities and limitations of interstellar travel that had started earlier in the day, and the reasoning was this:

• Our galaxy contains billions of stars like our sun, and many of those other suns are billions of years older than ours;
• If it’s common for stars like our sun to have Earth-like planets, some of those may have developed intelligent life and civilizations like our own;
• Some of those civilizations may have had a “head start” of billions of years on ours;
• They may have developed interstellar travel (which didn’t seem like a great stretch, since these 4 very guys — having recently unlocked the secrets of nuclear fission — had been discussing interstellar travel earlier that day and other civilizations might have had billions of years longer to have been thinking about it — consider the strides we’ve made in transportation in just a couple hundred years);
• Even at a “slow” pace of a fraction of the speed of light, it would only take a few million years for an interstellar-travelling civilization to cross the entirety of our Milky Way galaxy;
• So why hadn’t space aliens already landed on the White House lawn? Why hadn’t we seen evidence of them with telescopes, etc.?
• In short, “Where are they?”

The above set of questions would later be called the Fermi paradox. Today, there is a Wikipedia article about it, and it’s the subject of systematic and active study by astronomers, cosmologists, and astrobiologists. At the time Fermi first posed the question in 1950, it was immediately compelling to many scientists. Given a growing realization among them that “Earth-like” (wet, warm) planets were possibly abundant in our galaxy, it suggested that there might be some “Great Filter” that prevented intelligent civilizations like ours from either beginning or lasting long on those planets. Optimistically, the Great Filter was something related to the biological evolution of intelligent life, making us a unique or very rare success story. Pessimistically, intelligent life was fairly common but the Great Filter was some existential challenge that prevents intelligent civilizations from lasting very long. You have to imagine scientists in the 1950’s thinking, “like they all discover nuclear fission and then get in a fight and blow themselves up.” It was a conundrum, and the answer seemed important to the fate of humanity. Looking for evidence of the other civilizations that seemed like they should exist began to seem important.

A few years later in 1959, a pair of physicists, Giuseppe Cocconi and Philip Morrison, published a paper in one of the most selective scientific journals making the case that the best way to look for alien civilizations was to search for radio signals from them. Unlike light, which is blocked by interstellar dust, radio waves penetrate unobstructed through great distances of space. And, they reasoned, a civilization as advanced as or more advanced than ours would likely have learned to manipulate and communicate with radio like we have. Thus was born an international radio astronomy effort that persists to this day as the Search for Extraterrestrial Intelligence (SETI). By 1961, a group of scientists led by the astrophysicist, Frank Drake, and including a young Carl Sagan (whom some readers will remember as the writer and presenter of the 1980’s TV series, Cosmos) had boiled the Fermi paradox down to a short mathematical equation, called the Drake equation, that could be very efficiently written on a postage stamp:

• N is what the scientists wanted to know, the number of alien civilizations we can detect radio signals from;
• R_* is the rate of star formation (number of stars that form each year);
• f_p is the fraction of those stars with planets;
• n_p is the average number of planets, given a star has them, that are “Earth-like” (where life could potentially form);
• f_L is the fraction of those planets on which life does form;
• f_i is the fraction of those planets on which the life evolves intelligence;
• f_c is the fraction of those intelligent species that develop civilizations involving radio communications; and
• L (rather frighteningly) is the average lifetime of those civilizations.

This may seem silly, but it’s not. Boiling a nebulous question like, “Where are the aliens?” into a number of (at least potentially) quantifiable factors had the power of making a big question into a set of smaller questions that different groups of scientists could actually work on.

And they have. NASA’s many robotic missions in the decades since have had many scientific objectives, important of which have literally been to measure key terms in the Drake equation.

Starting in our own neighborhood, we’ve conducted a multitude of robotic missions to Mars, culminating with the landing and operation of 4 car-sized remote controlled rovers, 2 of which are driving around now. Geological evidence collected by these rovers has conclusively shown Mars had warm oceans and liquid water rushing across parts of its surface between 3 and 4 billion years ago. Mars today has weather and a climate, and climate models like those used on Earth actively predict its day-to-day weather conditions.

Our other planetary neighbor, Venus, has proven harder to explore in detail due to its current harsh surface conditions, but recent NASA models consistent with data from robotic missions and Earth-based observations suggest it could have had a water ocean and habitable temperatures for as much as 2 billion years of its early lifetime before it became a hellish place due to a runaway greenhouse effect.

We’ve also looked much further afield in search of planets beyond our solar system. Since 1995, astronomers have been able to observe stars with sufficient precision to detect the “wobble” caused by planets orbiting them. Since 2009, the Kepler space telescope has hunted planets by staring at a field of stars long enough to see the cyclic dimming as orbiting planets pass in front of them. The nature of each planet and its distance from its sun can be sorted out based on the extent and periodicity of the dimming.

Based on these explorations, we now know the following:

• Our own solar system, in its history, has hosted at least 2 and maybe 3 habitable planets.
• Planets are not static, and the habitability of a planet can change. Mars was once habitable, and now it isn’t (at least for complex life). Earth wasn’t always habitable for us. Before the Great Oxidation Event about 2 billion years ago, during which now-extinct bacteria began producing oxygen by photosynthesis, we wouldn’t have been able to breathe.
• f_p in the Drake equation, the fraction of stars with planets, is about 1. Just about every star you see in the night sky hosts at least 1 planet.
• n_p in the Drake equation, the average number of planets in a star’s “habitable zone” where water would be liquid, is about 0.2. That is, about 1 out of every 5 stars hosts a world that has the right temperature for life like our own.

To me, these discoveries are incredible. There are a lot of planets that could potentially host life, and even intelligent civilizations! But what are the chances that any one of them develops life, intelligent life, and a civilization like ours? And, how long does such a civilization typically last? We are still lacking any good information about the last 4 terms in the Drake equation (f_L, f_i, f_c, and L). It would seem we will be lacking that information for some time, since we so far only know of one intelligent civilization (us), and getting to other stars in reasonable time frames remains a substantial technical challenge.

In a 2016 paper, astrophysicist Adam Frank and astrobiologist Woody Sullivan showed that we can still make important conclusions about alien civilizations — conclusions relevant to our own project of civilization — with what we know now. The two scientists re-arranged the Drake equation to ask, not how many alien civilizations exist now, but an easier and still interesting question: How many alien civilizations have ever existed in the history of the observable universe? This question can be expressed in a re-formulated Drake equation:

Now, N_* is the total number of stars, which we know. There are about 2×10²² in the observable universe. We know the next two terms from astronomy work (see above), we have no idea about the following three terms, and the pesky L term (average lifetime of intelligent civilizations) is taken away because we are asking how many civilizations have ever existed in the observable universe, not how many exist right now. Frank & Sullivan combined the three remaining terms we don’t know into a single fraction, f_bt, which is the fraction of planets that have ever existed within the habitable zones of orbits around stars that go on to develop biology that results in a technological civilization:

Now, we can ask and answer the question, “What is the likelihood that we are alone in the history of the observable universe?” That is, what would f_bt, the probability that a habitable planet develops an intelligent civilization, have to be in order for N_ever to be just 1? We can calculate the answer based on what we know:

That is, for us to be alone in the history of the universe, the probability of a physically habitable planet developing a technological civilization would have to be less than 2.5×10^-22 — less than a 0.000000000000000000025% chance. To put that in context, the chance you will be struck by lightning 3 times during your lifetime is 1×10^-12. That’s a probability 4 trillion times larger than f_bt would have to be, given the sheer number of habitable planets, for us to be the lone civilization to have developed in the history of the universe. If we are the only one, then nature would have to be incredibly biased against the development of intelligent life.

There are optimists and pessimists. Since we’re talking probabilities, we’re all free to think what we want. As for me,

• I don’t generally fret that I might get struck by lightning 3 times; and
• The above math makes me think we are almost certainly not the only intelligent civilization to have faced the challenges of filling up its home planet. In fact, there have very likely been thousands. This is an amazing conclusion to ponder.

What wisdom can we glean from that knowledge? What common experiences might we share with, perhaps, thousands of alien civilizations possibly living, or having lived, on worlds our telescopes have already seen? Without crossing over to science fiction, what can we say we know about what an alien civilization might be like?

We know a defining feature of any civilization like ours would be its ability to harness energy from its planet’s star. Prior to civilization, each person had the energy of one person with which to do stuff. Now, if you live in an industrialized country, you probably use the equivalent of about 50 people’s energy every day just to control the temperature in your house. If you jump in your car that gets 25 mi/gal and start driving, you immediately begin using the energy equivalent of about 12 people. A fundamental feature of a civilization like ours is the ability to magnify our power by harnessing and directing a star’s energy. That’s exactly what we’re doing whenever we make a bonfire, drive a car, fly on an airplane, or send a text message. Dolphin’s and chimpanzees are smart. They use tools and communicate through language. But they don’t build fires. Each dolphin or chimpanzee has exactly the energy of one dolphin or chimpanzee at its disposal. They don’t harness additional energy from the sun; hence, they are not civilized.

Since we’ve spent decades studying other planets, we know pretty much for certain what sources of energy would be available for any intelligent aliens seeking to develop a civilization:

• Burning stuff (combustion). We started by burning trees, which stored energy from the sun and converted it to biomass over a period of years. Later, we discovered our Earth had given us a great gift: fossilized biomass (oil, gas, coal) from millions of years of its previous experiments with life. Most of the energy that fuels our civilization still comes from burning stuff.
• Hydro/Tides. If a planet has water or other liquids flowing on its surface, that motion can be harnessed to generate energy.
• Wind. If the planet’s atmosphere generates wind, the wind can be used to harvest energy.
• Solar. The planet’s star’s radiation energy can be directly harvested by low-tech (think black plastic), high-tech (think photo-voltaic), or organic (think photosynthesis) methods.
• Geothermal. Heat from deep within the planet, generated by storage of it’s star’s radiation or tidal energy, can be tapped by a civilization on the planet’s surface.
• Nuclear. If the planet has stores of radioactive elements like uranium, the energy evolved when they decay by nuclear fission can be captured and used. We also believe we may someday create energy by nuclear fusion — by fusing hydrogen molecules to make helium like the stars themselves do. But we haven’t yet proven it.

That’s pretty much the whole list. We know, because we’ve studied astronomically or sent robots to visit lots of planets and stars. Energy in the universe comes from stars, and stars shine on and gravitationally pull on planets, and those are the ways of directing star energy if you live on a planet.

To the extent that it’s successful, any alien civilization’s energy use will eventually affect its home planet. Some methods of energy use will affect the planet more strongly than others. In our case, as we’ve been studying in this series, burning stuff creates carbon dioxide which traps the sun’s radiation energy which heats the atmosphere and then the oceans.

What happens when the aliens’ population gets large, when it begins to fill up its home planet and when its energy use begins to create significant planetary responses?

In a 2018 paper, Adam Frank and three other scientists applied to this question the same type of math that was applied to Easter Island in Episode 8. In that episode, two linked mathematical equations, describing the growth of the human population on the island and the growth and consumption of the resources on which the humans depended, accurately predicted the early growth and eventual catastrophic collapse of the human population, as captured by the archaeological record.

Here, the scientists applied the same type of math to an entire planet (also a sort of island) inhabited by an intelligent, civilization building population. One equation modeled the population growth and its consumption of energy. A second, interdependent equation modeled the response (temperature rise) of the planet to the method of energy generation. There were two means of generating energy. The first (like fossil fuel combustion) caused a strong planetary response. The second (like solar) caused a mild planetary response. At some point (either soon or late after detecting the planetary response), the population could switch its energy generation method from the first method to the second method.

The scientists found four broad categories of solutions to their equations, depending on the rate at which the planet responded to the population’s energy generation and the timing of the population’s switch to the lower impact energy resource. The four different types of outcomes are shown in the plots below, where the solid line is the population and the dashed line is the planetary “temperature.”

Rather frighteningly, the most common outcome was some extent of a “die-off,” as shown in plot A. In these numerous scenarios, growth in high impact energy use drove a significant change in the planetary state that strongly reduced the planet’s capacity to support the population, even after the population switched to the lower impact energy source. This often resulted in significant population reduction before restoration of the planet to an equilibrium (though changed) state; in plot A, the surviving population was only about a third of the peak population. Two out of every 3 people died during the collapse.

Some simulations provided hope. Populations that switched to the more sustainable energy source early enough, relative to the planetary response, were able to achieve a soft approach to a sustained population, as shown in plot B.

Populations unable or unwilling to change to a sustainable resource were doomed to collapse, as shown in plot C. The time before collapse was dictated only by the rate of response of the planet.

Perhaps most scary of all was the type of scenario shown in plot D. In these scenarios, the population switched to the more sustainable resource, but too late. The planetary system and the population appeared to begin to stabilize, before suddenly rushing to collapse as planetary response feedbacks took over. This, I think, is one of the most underappreciated features of climate change. Geology is slow. We can already see at work glimmers of the types of positive feedbacks that, once underway, could drive our planet to a very different state despite our best efforts. Arctic ice melts, reducing the solar reflectivity of the entire Arctic region of the Earth, causing Earth to absorb more solar radiation. Thawing Arctic permafrost releases formerly trapped methane, a greenhouse gas 20 times as potent as carbon dioxide.

We can’t necessarily call off climate change when we decide we’ve had enough. The decision is time sensitive.

A cosmic test.

Why are we talking about aliens?

Here’s the thing. In American politics (which appear to be mirroring the politics of the democratic world), we are currently divided into two tribes. The voice of each tribe, through monetary distortions of the systems that elect our politicians, is dominated by the most extreme elements of the tribe. Each tribe is telling itself a story about climate change.

The story being told by the extreme elements of each tribe is objectively wrong.

The Story of Tribe #1. Humans are greedy. We are carelessly, wantonly destroying the Earth. From the beginning, the burning of fossil fuels was a nasty, unnatural method of fueling the fires of our greedy desires and Earth’s destruction. We are immorally destroying the planet, primarily in the service of the very rich. We should be ashamed for burning fossil fuels.

The Story of Tribe #2. The Earth and its resources are our birthright. We have used those resources, including fossil fuels, to great effect. Unburdened capitalism is beneficial, and has unleashed the full power of the human spirit. Limiting that progress with fake “evidence” of problems is immoral. The costs of addressing your unproven problems are unjustified. Even, “God had guaranteed us an ultimate solution to our problems.”

These are my own interpretations of the two extremes that currently animate us. Please forgive me any inaccuracies, and try to honestly answer whether you identify more strongly with one of them.

I, myself, identify more strongly with one of them (Tribe #1) but, having studied this for a year, I know it’s a mistaken position. We are not a greedy, evil species that’s wantonly consuming a helpless Earth. The Earth is fine. It was fine before there was oxygen in its atmosphere for us to breathe, and it may well be fine when the next life evolves that’s well adapted to the planetary temperature we create. Further, we are not some greedy, evil blight on the Earth because we burn fossil fuels. In fact, the fossil fuels were a gift from Earth’s previous life experiments. They are fundamental to us having built a civilization in which we can have this conversation. On any alien planet, given our understanding of astronomy and physics, the same energy resources would very likely be used first. We are not greedy and evil, we have just been trying to do what humans do — live comfortably, free ourselves from the threats of diseases and predators, raise kids. Earth’s fossil resources were a gift to us, one we have used to build our civilization, but one our scientific evidence tells us we dare not use much longer.

The story told by Tribe #2 is also problematic. The Earth is not our birthright. Our own solar system has featured at least one, and maybe two, other planets that have been habitable at one point but lost their habitability. There are no guarantees. The only protections we have from a bleak future, as a species, are knowledge and acting on that knowledge.

In fact, evidence gathered from significant study of both nearby and faraway worlds makes a strong case that the urgent challenge we currently face with climate change is a cosmic test that would face any intelligent, technological civilization on any planet in the universe. Further, it almost certainly has faced other alien civilizations already, perhaps thousands. It may well be the “Great Filter” proposed as one solution of the Fermi paradox.

This should focus our thinking. Just as much smart work has been required to prevent a potentially civilization-ending nuclear war, smart and coordinated work will be required to find our way through this challenge. We really have no excuse. Thanks to decades of work, we have the technology to switch to low-impact energy sources. The only thing standing in our way is our own ability to agree on a set of facts, compromise on a rational set of solutions, and execute. A basic law of life is “survival of the fittest,” and this is probably a cosmic test of our civilization’s societal fitness.

But what course of action can we all agree on? We need a framework in which we can make steady (and rapid) progress while still arguing about the details. I’ve put quite a bit of thought into that, and I’ve read widely over the last couple years. I believe there is such a framework. It’s a framework we’ve already used with great success (hint: it gave you your smart phone). It’s one that could ensure consistent progress, while allowing all of us the freedoms of choice we value.

That will be the subject of Episode 10. Stay tuned.

#rescuethatfrog

Note: Episodes 8 and 9 of this series rely heavily on ideas in the book, Light of the Stars: Alien Worlds and the Fate of the Earth, by Adam Frank (2018). I recommend it.