Earth in Human Hands

by David Grinspoon

  In some ways the ozone problem is a relatively easy one to solve compared to others that loom. In the larger scheme of things, the solution required relatively minor economic disruption. Nonetheless, it serves as an important “proof of concept.” Clearly we have the capacity for global changes of the fourth kind. There is nothing impossible or magical about the transition from inadvertent to intentional planetary change.

  There are other success stories. The fight against infectious diseases is notable here, an ongoing struggle that has in many ways been made more difficult by the modern vectors of worldwide trade and travel. Yet the global public health community has accomplished miracles and wonders. One Anthropocene extinction that will not provoke too much mourning is the elimination of the smallpox virus from the planet. The near accomplishment of this merciful task has been possible only through a huge planetary-scale coordinated effort.*

  The Twisted Gift of Global Warming

  I’ll give a few more illustrations of planetary changes of the fourth kind. They range from fully or nearly achieved global goals, to urgent near-term priorities, to far-future possibilities sometimes explored in science fiction. What these examples have in common is that they are all purposefully chosen planetary-scale changes.

  Among these, the most pressing goal is the relinquishment of fossil fuels and the diversification of energy sources required to keep global warming in check. This is a change, a global project, that is currently under discussion. When I’ve said this at lectures for savvy audiences in Washington, DC, that the problem is “under discussion,” it has sometimes elicited ripples of mordant laughter from the cognoscenti. Chalk that up to my killer comic timing, but I don’t mean it as a joke. Yes, of course the actions mustered thus far seem like too little too late. At this writing it appears that there is virtually no way we will be able to avoid some level of global catastrophic change as a result of our carbon emissions. The ultimate magnitude of these changes, and whether we can act to avert a massive twenty-first-century human disaster, one on the scale of the tragic global conflicts and famines of the twentieth century, is still an open question, one of the great dramas of our age. Its outcome hinges on the uncertain interactions between two complex systems, both impossible to predict in detail: mass human behavior and the response of the global climate system. Yet things have moved hugely in that there is now widespread global awareness of this situation, with much fevered debate and gnashing of teeth. The existence of this agitated global conversation is something new and positive.

  We scientists have been discussing the problem for half a century, at first as a somewhat abstract concern and then with an increasing sense of reality and urgency. It started to emerge as a visible public policy question in the 1980s. A key milestone was the testimony of climatologist Jim Hansen before the U.S. Congress in June 1988, during which he declared that “It is time to stop waffling so much and say that the evidence is pretty strong that the greenhouse effect is here.”2

  The more widespread debate really only started up, however, in the mid-2000s. The film An Inconvenient Truth, which helped launch a more visible public discourse, first in the United States and then worldwide, was released in 2006. Consensus on answers may still be sorely lacking, but the question is now undeniably on the world’s radar screen. Whether or not any solutions enacted this year, or next year, are to your liking, or seem equal to the problem at hand, the emergence of this global awareness and deliberation is a hugely significant change, and a necessary prelude to any substantive action.

  Keep in mind that we have never dealt with anything like this before. How will we power our global civilization without wrecking the natural systems upon which we, and the rest of the biosphere, depend? With this question there is a sense in which global humanity is trying to make up its mind about something important for the very first time.

  To put it mildly, not everyone agrees on the answer. Yet now the question looms large, even for those who put all their energy into trying to wish or talk it away. It is not going away. Around the world, everyone—at least those who are not completely consumed with warfare or daily survival—is talking about it. To those who are filled with urgent concern this seems to be happening very slowly. However, considering how hard it is for this problem to compete for people’s attention with concerns that seem more immediate and pressing, and how long it takes for an idea to diffuse around the globe and sink in to wide public consciousness, this is actually a rapid change in the right direction. Maybe this comes from my perspective as a planetary scientist, where anything changing on the scale of a decade seems lightning fast. To some of us who model planetary radiation balance, who were following this for many decades before anyone else was paying attention, it’s a huge relief that now everyone is.

  This is only one of many issues that will force us to confront ourselves as global actors in order to maintain a thriving civilization, but it is the first one to get our attention in this way. Perhaps it is at first shaking us too gently, but it is awakening us to our planetary nature. This is the twisted gift of global warming.

  Planetary Defense

  What else goes in this category of purposeful interference with the fate of the Earth? Active defense against dangerous asteroids and comets. As I describe in chapter 1, a big insight from planetary exploration has been the important role played by small bodies crashing into larger ones. Earth has suffered catastrophic collisions, and will do so in the future, unless we (or others) intervene. Studies of cratered surfaces throughout the solar system and telescopic surveys of the population of small orbiting objects give us a rough idea of the level of danger, the “expectation frequency,” of impacts of a given size. Some historical events remind us that the threat is real. On June 30, 1908, a small comet exploded over the remote forest near the Tunguska River, in Russia, flattening some eighty million trees and generating a powerful shock wave that knocked people off their feet hundreds of miles away. This was the largest impact explosion in recorded history, with an estimated energy equivalent of some ten to thirty megatons of TNT, or roughly the yield of the largest nuclear bombs ever built. Had this occurred close to a modern city, it could have caused millions of casualties.

  Impacts from space are an ongoing phenomenon, with the smaller objects arriving much more frequently. In February 2014 a tiny* asteroid entered the atmosphere over Chelyabinsk, Russia, formed a meteor that appeared brighter than the Sun and then exploded, causing thousands of injuries, many to people who had been drawn to windows by the initial glow, only to have the blast wave splatter them with broken glass. It’s just a matter of time before our luck runs out and an inhabited area suffers a more catastrophic impact. These historically recent impacts, including potential city destroyers such as Tunguska, are small potatoes in planetary history, not world-changing events of evolutionary significance.

  There are some real monsters lurking out there. Every one hundred million years or so, on average, Earth gets clobbered by an object greater than six miles across, the size of the end-Cretaceous impactor, the one that did in the dinosaurs. Smaller (but still sizable) bodies fall more frequently. A half-mile-diameter object could cause a short-lived but intense climate disaster, raising enough dust to seriously disrupt global agriculture for long enough to cause mass starvation. There is about a one-in-five-thousand chance of something this size hitting Earth in the next century. Depending on where it fell, it could cause other horrible effects, such as gargantuan, historically unprecedented tsunami waves sweeping over densely populated continents. However, we are no longer helpless against such outrageous misfortunes. Science to the rescue. We now can detect, and likely intercept, such an intruder.

  Planetary defense is being taken seriously in the planetary science and space engineering communities, and several defense mechanisms are currently being studied. Probably the worst idea, although it makes for flashy Hollywood movie plots, is to send up a nuke and blow the offending object to bits. Instead of one giant asteroid heading for E
arth, you might now have an unstoppable radioactive swarm of smaller objects. More promising is the idea of affixing small thrusters to an asteroid and gently pushing it off its collision course. If the interloper were identified many years out from its projected impact date, then a small change in trajectory would be enough. Or, if we used a “gravity tractor,” we wouldn’t even have to touch the wrong-way asteroid: park a massive spacecraft alongside it, and the gravitational force acting over time will be sufficient to pull it into a nonmenacing path.

  We don’t yet have a planetary defense system in place, but there are many feasible ideas. No matter what, the first step is simply identifying the objects out there that might pose a threat. Several observational programs are under way to do just that. Unless we discover a dangerous object that is going to hit in the next decade or two, a possibility that diminishes as our telescopic surveys improve, we should have plenty of time to stop a monster asteroid.

  I am slightly more concerned about the possibility of a dangerous comet heading our way. Unlike the asteroids (rocky and metallic remnants of planet formation that mostly wander the inner solar system and a vast belt between Mars and Jupiter), the icy comets lurk, largely undetected, in the cold, dark outer fringes of the solar system. We know that comets can also impact Earth, and one might be harder to thwart than an asteroid.

  In 1994, the eyes of the world’s astronomers were glued to telescopes trained on Jupiter to watch as pieces of Comet Shoemaker–Levy 9, gravitationally disrupted by a previous near miss with Jupiter, and strung out into a line of icy fragments, smashed one by one into the swirling atmosphere of the giant planet. With some friends, I watched it happen through a telescope at the University of Colorado in Boulder. It was quite the spectacle, the giant, dark impact scars appearing and then rotating around with the planet—breathtaking, and both comforting and disturbing. The fact that the predicted timing of the impacts was exactly correct was reassuring. We really are pretty good at detecting orbiting objects and predicting their motions with incredible accuracy. That part we have down. When a respected dynamical astronomer declares that a certain object will or will not hit Earth in such-and-such a year, you should believe her. Still, it was a little disorienting, strange, and surreal to see these large black flaws suddenly appear: enormous new features abruptly altering the age-old familiar geography of the bright, banded giant. It was also surprising to realize the extent to which nobody knew how to predict the consequences of these impacts on Jupiter itself. The range of predicted effects was huge, from massive visible flashes to barely noticeable changes. Observing the outcome in real time, with our own eyes affixed to telescope eyepieces as well as a battery of instruments measuring the flash and the aftereffects, was awe-inspiring and instructive. The experience reminded us vividly that violent planetary collisions are a fact of life in the modern solar system, not only something that happened in the ancient past.

  In January 2013, sharp-eyed Australian telescopic observer Rob McNaught found a new comet. This in itself was not surprising. He’s discovered more than eighty of them. Once, when I was but a wee postdoc, I spent an evening observing with him through his telescope at Siding Spring Observatory, in eastern Australia, after a day spent exploring the adjacent Warrumbungle National Park, where I first saw tree-nested koalas and galloping emus. When night fell, I had my first really good look at the southern sky, another wild new landscape populated with exotic beasts. I could not have had a better guide, and with McNaught’s deep-sky familiarity and encyclopedic knowledge, it was clear that he would instantly notice any faint intruders wandering into this territory. Yet what was surprising about this particular new comet was that it seemed to be on a direct path to collide with the planet Mars on October 19, 2014. Initial estimates suggested that the icy nucleus of the comet was possibly up to thirty miles across, much larger than the doomsday object that struck Earth sixty-five million years ago, leaving fire, darkness, and mass extinction in its wake.

  Such a colossal collision might spell big trouble for our spacecraft currently at Mars, but, man, would it ever provide us with front-row seats to a phenomenal planet-shaking collision. And you thought the Shoemaker–Levy 9 smash-up with Jupiter in 1994 was cool! Adding to the strange sense of celestial coincidence, this comet was fated to arrive at Mars less than a month after two new spacecraft. NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) entered orbit on September 22, followed by India’s Mars Orbiter Mission on September 27.

  As it turned out (unfortunately?), upon further observation and calculation, this comet was much smaller, less than half a mile across, and would miss Mars by about eighty thousand miles. This was still close enough to splatter the atmosphere with hydrogen and dust, producing atmospheric effects that were observable with telescopes and spacecraft. When the close approach occurred, it provided a great opportunity to learn more about the infrequent (on human timescales) but inevitable interactions of planets with comets. For me there was also an unsettling aspect. We hear more about the impact threat from stray near-Earth asteroids, but a comet like this one, plunging at a frightening pace from the dark periphery of the solar system, would be a more formidable threat. In contrast to the many years or even decades of warning we’d likely have for a menacing asteroid, a comet can appear with little notice. This Martian near miss occurred less than two years after McNaught’s discovery. If the wrong comet appeared, we might have only a similar warning interval between detection and Earth impact. The chances of this happening in any year are minuscule, but recent solar system history teaches us that, if we watch long enough, seemingly unlikely objects and events will eventually materialize. Such incidents remind us that the apparent isolation of planetary distance can be abruptly shattered and that, given enough time, the constancy and the safety of our world are illusory.

  Most likely, assuming that our civilization sticks around on this planet for another few centuries, by the time another truly scary comet comes our way we’ll have systems in place to detect and deflect it. In the meantime, I’m glad (for many reasons) that we are continuing to send spacecraft to comets and asteroids. In addition to providing pretty pictures and new information about planetary origins, such missions are also valuable for the longer-term project of threat mitigation. Deepened understanding of cometary structure and evolution will sharpen our ideas about how to redirect or disrupt one, should that be necessary one day. And I’m glad that the Rob McNaughts of this world are keeping watch for anything new coming in our direction.

  The comet threat, while smaller, is also less predictable, and one could strike with little warning. So, once we ascertain that there are no threatening asteroids currently out there, we still shouldn’t wait too long to design some kind of deflection capacity. We’ll need it someday.* The creation of a planetary defense system will be an important event not just for humanity, but in the life of the planet: it will be that moment in planetary evolution at which life first develops the capacity to avert a threat that has been hanging over it since the world was born.

  The Big Payback

  If we hope to be an enduring entity on this planet, we need to start thinking like one. Asteroid defense need not currently be our most pressing concern, but it is in a category that we need to get much better at dealing with: those threats that lurk and linger, that are not imminent but are also not going anywhere, that will eventually be our undoing if we don’t address them.

  Just as we have unwittingly become global actors, we have also become long-term actors. We’ve set in motion processes that will play out over centuries and millennia. We are acting on multigenerational timescales, but there’s nobody in charge of long-range planning, nobody remaining at the helm long enough to see obstacles coming at long distances down the time stream, and steer around them rather than into them. Unless we want to be driving blind, we have to have some awareness of where we’re going on the larger scales, both spatial and temporal, on which we’re now acting.

  Once, our biggest worries ca
me and went with seasonal cycles. Biological evolution had no reason to equip us for problems spanning longer than a human lifetime.* There’s no reason our cognitive tool kit, well evolved to deal with Paleolithic survival challenges, should include the ability to think ten thousand years into the future. But we are also creatures of culture. When we began to develop oral histories and make plans together, probably first for hunting game, we transcended our genetic capacities. By telling stories, we found new sources of resilience, new ways to incorporate past experiences and meet future challenges. Now it is up to us to adapt again. We’re awakening to several threats, some of our own making, that will require us to maintain constant attention, and action, over centuries and millennia. We need to continue to expand our time horizons. Cultural evolution has equipped us with institutions that endure for decades and centuries, but not too many that have maintained continuity over millennia. Religions are exceptions, and whatever institutions we develop to deal with asteroid defense or other very-long-term endeavors may have something to learn from those that have persevered.

  We have a deficit of sustained attention, but this disorder seems especially acute today. We’ve never needed a long-term outlook more than we do now. Yet, at the same time, as the pace of technological and social change quickens, both the past and the future seem to recede in a fog of electronic distraction. Sometimes it seems we can barely hope to master the elusive present. However, technology has also gifted us with greater access to our past than we have ever enjoyed, in burgeoning scientific knowledge of the history of our species, biosphere, planet, and universe, in unprecedented instantaneous access to vast treasures of knowledge, and in the ability to share stories, old and new, with a global community. Likewise, our capacities for transmitting knowledge to our descendants, and for forecasting and modeling future challenges, are growing in seemingly boundless ways. An expanding connection to the past and future is at our fingertips.