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In this column, we'll be talking about terraforming. But rather than considering what we would need to do to transform Venus, Mars, or one of Jupiter's moons to make it Earthlike, we'll be talking about terraforming our own planet. As global climate change progresses, we need to consider making some environmental adjustments to keep the Earth suited to human habitation.
We'll tell you about a potential climatic disaster that makes the currently projected disaster look like chump change. We'll consider how a mass extinction event that took place some 12,000 years ago has contributed to that disaster. We'll discuss the ecological role of the wooly mammoth (Pat's favorite extinct critter) and we'll end with a research project that's attempting to avert disaster by restoring the ecosystem that was dominant in the Arctic in the late Pleistocene.
But before we get to the global disaster that will change the world as we know it, let's consider a disaster you may have experienced personally. Have you ever had a power failure that turned off the electricity to your freezer? Being a savvy science-minded sort, you probably know that you should keep the freezer door closed when the power goes out. The door is insulated and keeping it closed will keep food cold and frozen for up to two days. After a few days without power the reason for keeping the door closed changes: opening that door will release an overpowering stench—gases released by the rotting food.
Keep that in mind as we talk about the Arctic, the Earth's freezer in the Northern Hemisphere.
In the Arctic lands that border the Arctic Ocean, the North Atlantic, and the North Pacific, there are vast landscapes underlain by permafrost. Permafrost is the name for soil that has been continuously frozen for two years or more. (Writing that makes Paul realize he has some permafrost pork chops in his freezer.) Some permafrost has been frozen for thousands of years.
You may think of the Arctic as perpetually snow covered. But in the summer, when temperatures rise above freezing, there is an explosion of life. The uppermost layer of the permafrost thaws. With twenty-four-hour sunlight and plenty of water, mosses, shrubs, and grasses flourish. Those plants use sunlight to remove carbon dioxide from the air and combine it with water to create the carbohydrates that make up plant matter.
When winter returns, the ground freezes and the plants die. But temperatures are so low that the dead vegetation doesn't decompose and rot. It just stays put, adding a small layer of organic matter to the top of the permafrost. Those summertime plants are basically taking carbon dioxide from the air and storing it in the Arctic freezer in the form of carbohydrates.
The next summer, the top layer of the soil thaws. That thawed region (known as the active layer) is about the same thickness as the previous year. But plant matter was added to the top of the soil during the previous summer. So the frozen bottom of the active layer isn't as deep as it was the year before. There's just a little more permafrost.
As a result, the permafrost layer increases in thickness each year, growing upward with the addition of dead plant matter. In some places, organic material is stored in frozen layers hundreds of feet thick.
All this adds up to a lot of carbon stored in the Arctic freezer. Scientists have calculated that there is currently almost twice as much carbon stored in permafrost as there is in the entire atmosphere of the Earth.
Plant matter that has been added to the permafrost over thousands of year will keep that carbon dioxide stored away only as long as the Arctic remains frozen. But the planet is warming and average temperatures in the Arctic are rising even faster than they are on the rest of the planet. Researchers who monitor permafrost temperatures have noticed a trend—the temperature deep in the permafrost has been rising. In some areas, melting permafrost has resulted in "drunken forests" where trees tilt at crazy angles. As the frozen soil in which the trees grew turns to mush, their roots are no longer held fast and the trees lean this way and that.
Currently the Arctic is still storing away more carbon than it is releasing. But as warming continues, that balance will change. And when it does, the melting of the permafrost will have implications far more significant than trees that appear to have had one too many.
Like the food in your freezer when the power is out, the organic material stored in the permafrost will rot when it warms up. Exactly how it rots depends on the microorganisms that produce the rot. If oxygen is available, microorganisms digest the organic plant matter in a process that's aerobic (a fancy way of saying "with air"). That process breaks the carbohydrates down to make carbon dioxide and water, releasing the carbon dioxide into the atmosphere.
Since carbon dioxide is a greenhouse gas, more carbon dioxide means a warmer atmosphere, and a warmer atmosphere means more permafrost melting. This unfortunate state of affairs is what scientists call a positive feedback process.
But wait! There is even more bad news. If no oxygen is available, microorganisms digest the plant matter in a process that's anaerobic (that means, as we're sure you guessed, "without air"). Rather than releasing carbon dioxide, the anaerobic process releases methane in a process known as methanogenesis (a fancy way of saying "making methane"). Methane is an even more potent greenhouse gas than carbon dioxide. It is more than twenty times better at absorbing infrared radiation (and warming the planet) than carbon dioxide is.
In many areas, methane from melting permafrost bubbles up through the water in the summer and is trapped under the ice in the winter. (To see great footage of scientists setting fire to methane bubbles, we suggest searching Youtube for "exploding under-ice methane gas in Siberia" or "Hunting for methane with Katey Walter Anthony." Believe us—this is footage worth looking for.)
For those of you who are striving to make lemonade out of lemons, there's some slightly good news. Over the course of ten years or so, other microorganisms eventually consume methane in the atmosphere. But that slightly good news has bad news attached. Those microorganisms use oxygen to turn the methane into carbon dioxide and water. The carbon dioxide then lives in the atmosphere for hundreds of years. So one way or the other, we get more greenhouse gas.
Greenhouse gases from the melting permafrost will add to the greenhouse gases released by burning fossil fuels. Hundreds of millions of years ago, plants removed carbon from the atmosphere. Those plants died and were buried, becoming coal, oil, and natural gas. When those fuels burn, the carbon that was safely stored away is set free once again to absorb solar infrared radiation and warm the earth.
The increased greenhouse gases from the melting permafrost could have many negative effects, but one sure thing is this: sea level will rise. Why? There are two primary reasons: 1) glaciers will melt and add water to the ocean, and 2) ocean water expands as it warms up.
Since the beginning of the industrial revolution, sea levels have risen about nine inches. Recently, the rate of sea level rise has been accelerating. As any physicist can tell you, acceleration means rapid change. The acceleration also leads to a wide range of predictions for the future. A very conservative estimate is that sea level will rise three feet by 2100, and could rise by six feet. The Exploratorium in San Francisco (where Paul works) is on a pier and can handle a three-foot rise, but six feet will cause problems for almost every pier in San Francisco and lots of low-lying seashore around the world.
But wait—we aren't done with the bad news! Carbon dioxide stays in the atmosphere for hundreds of years. Over that time, temperatures will increase enough to partially melt the glaciers of Greenland as well as the West Antarctic ice sheet. This would raise sea level by twenty feet or more.
By this time, you may be wondering how much sea level can change. Short answer: a lot. At the end of the last ice age, sea level rose by over 300 feet. That rise in sea level created such useful ocean-water-filled features as San Francisco Bay. Over thousands of years, if we burn all available fossil fuel and melt the permafrost, we could melt the entire ice sheets of Antarctica and Greenland, raising sea level by 200 feet. That rise in sea level would put Pat on an island that used to be one of the hills of San Francisco; Paul would be in a houseboat anchored in a hundred feet of water over what used to be Mountain View.
That takes us to Russian scientist Sergey Zimov and his plan to slow the melting of the permafrost.
Zimov is the director of the Northeast Science Station, located near the Russian town of Chersky, just north of the Arctic Circle. Here, permafrost lies beneath bogs filled with water and dead vegetation and covered by a layer of moss. The moss ensures the landscape stays soggy—moss has no roots to pull water up from the soil and it releases little water to the air.
Unfortunately, this moss-covered tundra is terrible for keeping the permafrost frozen. Dark in color, it absorbs solar energy, warming the ground and melting the permafrost. To slow the melting of the permafrost it would be good to reflect more sunlight back into space. Snow cover would do the trick—it reflects a lot of sunlight, keeping the surface it covers cool. But alas—the warming climate removes snow cover.
Fortunately, snow isn't the only surface that is good at reflecting sunlight. Consider a lush meadow, filled with grass. If you took a photo of that meadow in infrared light, you'd see an alien world in which each blade of grass looks bright and white, glowing against a dark background of rock and soil. The grass blades look white because leaves reflect infrared energy. That makes them a great covering for an area you want to stay cool.
If grasslands could replace the mosses that now cover the permafrost, the warming of the permafrost could be slowed down. The grass would reflect infrared light and keep the ground cooler. But how could thousands of square miles of Arctic bog be turned into grassland?
That's where Sergey Zimov comes in. He has pointed out that the bogs that cover the permafrost are recent, geologically speaking. Go back to the Pleistocene, and you'd see a very different environment.
The Pleistocene lasted a long time, starting some two million years ago and ending a mere 12,000 years ago, give or take a few centuries. It was a time of vast glaciers, which advanced and retreated in a cycle that repeated many times over the years. During all this time, the Siberian tundra was a grassland, now called the Mammoth Steppe. At the end of the last ice age, the Mammoth Steppe was the world's most extensive ecosystem, stretching from the northern areas of Europe and Asia, across the Bering Strait and into northern North America.
This vast grassland supported enormous populations of large grazing animals. The density of grazers was comparable to that of today's African savannah. But instead of zebra, wildebeests, antelope, elephants, and the like, these grazers were wooly mammoths and wooly rhino, along with cold-adapted grazing animals that still exist—like bison and musk ox and horses.
By analyzing bones collected in Siberia, scientists have calculated that animals were abundant even during the coldest periods of the Pleistocene. A single square kilometer of steppe would have ten tons of animal biomass. That's the equivalent of a mammoth, five bison, six horses and ten reindeer.
Just over 11,000 years ago, all that changed. The mammals of the Mammoth Steppe disappeared in a mass extinction that happened over a relatively short time period near the end of the ice age.
They disappeared at the same time that human hunters of the Clovis culture appeared in North America. Paleontologists argue over whether humans could drive large animals to extinction over the entire area of North America, but they are confident of one thing. Humans arrived in North America and a thousand years later all the large animals were gone.
Paleontologists have found sites where the characteristic fluted Clovis pointed spears are found together with the remains of large mammals with cuts on the bones showing that the animals were slaughtered. They point out that when humans occupied an island, even one as big as New Zealand, large animals disappeared. The disappearance of the grazing animals may not have been entirely due to humans eating the animals—human agricultural practices involving burning large areas and human introduction of domestic animals may also have contributed to the demise of the larger animals. But Paul answers without hesitation when asked what happened to the mammoths. "We ate them," he says.
And with the disappearance of the animals (eaten or otherwise disappeared), the Mammoth Steppe vanished as well. The grassland gave way to mossy bogs.
The Mammoth Steppe was a stable environment. It had developed over hundreds of thousands of years and had survived glacial periods and warm periods. But without the grazing animals, the environment changed.
Every environmentalist knows that animals need the right habitat to thrive. Destruction of habitat is generally considered to be the most significant cause of extinction worldwide. Without the bamboo forest, giant pandas can't survive. Without old growth forest, there are no spotted owls.
But it may be less obvious that the habitat also needs the animals. The kelp forest off the coast of California, for example, needs sea otters to remain healthy. The otters prey on sea urchins. Without the otters, sea urchins overgraze on the kelp, creating "urchin barrens," areas with many urchins and no kelp. The African savannah needs elephants to weed out trees and shrubs. Without elephants, these plants transform the grassland into forest.
Sergey Zimov contends that the grassland of the Mammoth Steppe did not disappear because of climate change. Instead, he believes mosses and shrubs overtook the Mammoth Steppe because the mammoths and other large grazers were no longer there to maintain it.
According to Zimov, those grazing animals provided a service that was essential to the survival of the Siberian grassland. They ate the grass. That may not seem like a boon to the grass, but it is. Unlike most plants, grass grows from the bottom of its stem, not from the top. This allows grass to do just fine in the presence of grazing animals. The animals eat the top off the grass, and the bottom, still safe and healthy, pushes up more leaf to harvest sunlight.
And the great hairy beasts of the Mammoth Steppe very efficiently processed the grass they ate. In the belly of the beasts, dead vegetation changes into something grassland desperately needs—an excellent fertilizer in the form of manure. Without the grazers to digest the grass, dead grasses accumulate. (Those bogs are clogged with dead vegetation, remember?) As long as the dead grass remained intact, the nutrients it contained were trapped, unavailable to new growth.
But that's not the only service the grazers provided. As herds of large animals trample over a carpet of moss, their hooves cut through the moss, breaking it up and letting grasses gain a foothold. Unlike mosses, grasses suck water from the soil and release it into the air in the process of transpiration, drying the boggy ground. All of this disrupts the moss community and helps the grass return.
So far, this has been a lesson in prehistoric biology. But now our story turns into something a lot more like a science fiction novel. Many classic science fiction concepts can be reduced to a question that begins with the words: "What if…?"
In this case, the question is: What if the grazing animals came back? That is the question that Sergey Zimov is working to answer with an ambitious project that he calls "Pleistocene Park." In a six-square-mile, fenced plot of tundra, he is testing a form of reverse geoengineering intended to restore the landscape to its Pleistocene state by reintroducing grazing animals.
Of course, it's tough to reintroduce animals that no longer exist, so he's had to improvise. The local species of wild horse was killed off 300 years ago, but Zimov gathered a herd of Yakutian horses, a variety that has a layer of fat on to keep it warm through the winter. He wrote to the king of Sweden to ask for some reindeer—they're raised commercially there. The bison native to the area are extinct, but the Canadian government gave him some modern bison. A reserve in Alaska provided some musk oxen. Into the Pleistocene park enclosure, Zimov introduced five major herbivore species: bison, musk ox, moose, horses, and reindeer.
What about the mammoth? Yes, we asked that, too. Live mammoths are just not available anymore and the frozen variety (occasionally found in the permafrost) is not useful for grazing. As good sf readers, we know that you are advocating for mammoth cloning just about now, but Zimov and Pleistocene Park aren't waiting for that.
Zimov needed the power of a mammoth to cut a path through the shrubs and trees, so he found a practical and immediate solution. He bought a tank. Yes, a genuine decommissioned Soviet tank, which pulverizes any tree or shrub in its way. Visitors to Pleistocene Park report that it's easy to see where the tank has been driven—years after it passed through the tundra forest, a trail of lush grass marks its path.
Zimov's reverse engineering is working. Conversion from moss-covered bogs to dry grassland has happened surprisingly quickly. Zimov talks of expanding the project, of bringing in predators like wolves and tigers to control the herbivore population. To create a modern Mammoth Steppe ecosystem, he'll have to go big—really big.
There's a wonderfully science fictional quality about the whole idea. There's something appealing about changing the environment by bringing back the animals that our hungry ancestors had for dinner. There's something downright charming about knocking down trees with a tank because you don't have a mammoth around.
Maybe it does seem a little crazy, but it's certainly not the first time people have made an effort to alter the planet on a grand scale. Every city that's been built, every harbor that's been dredged, every river that's been dammed, every forest cleared for agricultural use is an example of human engineered environmental change. What's different here is the mindful use of environmental processes to transform—and restore—the environment on a grand scale.
Paul Doherty works at The Exploratorium, San Francisco's museum of science, art, and human perception—where science and science fiction meet. For more on Paul's work and his latest adventures, visit www.exo.net/~pauld. Pat Murphy is a science writer, a science fiction writer, and occasionally a troublemaker. She works at Mystery Science, developing hands-on lessons for elementary school. You can learn more about what she's up to at www.brazenhussies.net/Murphy.
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