The World in 2050: Four Forces Shaping Civilization's Northern Future

nourished on their tops by snow. They are removed at their margins by melting and—if they float out into an ocean or lake—by calving off icebergs into the water. When nourishment exceeds removal, glaciers grow, storing water up on land, so sea level falls. When removal exceeds nourishment, glaciers retreat and their stored water returns to the ocean. In this way sea levels have danced in a tight waltz with glaciers, falling and rising anywhere from about 130 meters lower to 4-6 meters higher than today over the past few ice ages. Other things—especially thermal expansion of ocean water as it warms—also drive sea level, but the waxing and waning of land ice is a huge driver.

As the last ice age unraveled, sea levels commonly rose 1 meter per century, and sometimes as fast as 4 meters per century during intervals of very rapid glacier melting.⁵⁰¹ Looking forward, if average air temperatures over Greenland rise by another +3°C or so, its huge ice sheet, too, must eventually disappear. Depending on how hot we allow the greenhouse effect to become, this will take anywhere from one thousand to several thousand years, raising global average sea level by another 7 meters or so.

Based on the emissions scenarios currently being bandied about by policy makers, the temperature threshold to begin this process will indeed be crossed in this century, and the long, slow decline of Greenland’s ice sheet will begin.⁵⁰² It is already something of a stubborn relic of the last ice age; if it magically disappeared off the island tomorrow, it’s doubtful this ice sheet could grow back.⁵⁰³ One thousand years from now, eighteen of the twenty-seven megacities of 2025 listed in Chapter 2 will lie partially or wholly beneath ocean water that might once have been blue ice in Greenland.⁵⁰⁴

But over the shorter term, meaning between now and the next century or two, the scary genie of Greenland and Antarctica isn’t from their ice sheets melting per se (indeed, it will never become warm enough at the South Pole for widespread melting to occur there) but from their giant frozen rumbling ribbons of ice that slide over hundreds of miles of land to dump icebergs into the sea. Already, there are many such ice streams in Antarctica and Greenland moving tens of meters to more than ten thousand meters per year. They empty out the deep frozen hearts of these ice sheets, where temperatures are so cold the surface never melts at all.

Of grave concern is collapse of the West Antarctic Ice Sheet. This vast area is like a miniature continent of ice towering out of the ocean, much of it frozen to bedrock lying below sea level. If it became unstuck, a great many Antarctic glaciers would start lumbering toward the water, eventually raising average global sea level by around five meters. There is geological evidence that this has happened before,⁵⁰⁵ and if it happens again it would hit the United States especially hard. For various reasons a rise in global average sea level does not translate to the same increase everywhere—water will rise by more than the average amount in some places and less than the average in others.⁵⁰⁶ Such a collapse would produce above-average inundation of the Gulf Coast and eastern seaboard, putting Miami, Washington, D.C., New Orleans, and much of the Gulf Coast underwater. When it comes to climate genies, the West Antarctic Ice Sheet is an ugly-looking lamp.

Frankly, we don’t understand the physics of sliding glaciers and ice sheet collapses well enough yet to model the futures of Greenland and Antarctica with confidence. Many things affect the speed and dynamics of that long slide that are hard to measure or see. They include the interplay between the sliding ice and its bed, the heat and lubrication added by meltwater percolating to the bed from the surface, the importance of buttressing ice shelves (which help dam ice up on the land), the ocean water temperature at the ice edge, and others.⁵⁰⁷ Computer models and field studies—like the one Jason and I were conducting in Greenland—are in their infancy. Scientists are still discovering new things and debating what may or may not be important. This is why the likelihood of accelerated sea-level rise was kept out of the last IPCC assessment, and may be kept out of the next one as well. Might the ice sheets start slipping faster, with higher sea levels right behind? Perhaps—but without well-constrained models, we don’t yet know how likely that is.

Genie in the Ground

Digging into a permafrost landscape usually goes something like this: After cutting through a thick living mat of vegetation, the spade turns over a dark, organic-rich soil, almost like the mulch that one buys to spread in a garden. Usually there are bits and pieces of old dead plants poking out of it. Then, anywhere from several to tens of inches down, the blade goes chunk and will bite no farther. But it’s not a stone. At the bottom of the hole, there is just more of the same organic-rich goop but it is frozen hard as cement, often with a little black ice peeking through. Going any deeper is a major job, requiring a big drill and lots of manpower.

Why on Earth would anybody go all the way to the Arctic to drill holes into frozen black muck? The reason is organic carbon, and we now know that frozen northern soils hold more of it than any other landscape on Earth. In fact, the more we study these soils the more carbon we find. As of 2010 the latest estimate is 1,672 billion tons (gigatons) of pure organic carbon frozen in the ground.⁵⁰⁸ That’s roughly half of the world’s total soil carbon crammed into just 12% of its land area.

The reason there’s so much carbon there is because this is a place too cold and damp for living things to fully rot away when they die. Live plants draw down fresh carbon from the atmosphere and store it in their tissues. When they die, decomposing microbes chow down, pumping the carbon back to the atmosphere in the form of carbon dioxide (CO₂) or methane (CH₄) greenhouse gases. But while plants and trees can still grow in cold places, even on top of permafrost, the microbes are hard pressed to finish off their remains because their metabolisms are strongly temperature-dependent (just as stored food decomposes more slowly in a refrigerator than at room temperature). Very often a mulch-like layer of peat will accumulate, building up the ground elevation over time as successive generations of plants root into the semirotted remains of their ancestors. Some decomposition continues underground, but once permafrost sets in, even that halts, and the stuff becomes cryogenically preserved. Since the end of the last ice age, this excess of plant production over plant decomposition has slowly accumulated one of the biggest stockpiles of organic carbon on Earth.

To put that earlier 1,672 gigatons (Gt) of carbon estimate into greater perspective, all of the world’s living plants hold about 650 Gt. The atmosphere now holds about 730 Gt of carbon, up from 360 Gt during the last ice age and 560 Gt before industrialization. The world’s remaining proven reserves of conventional oil hold about 145 Gt of carbon and coal about 632 Gt. Each year we release around 6.5 Gt of carbon from burning fossil fuels and making cement. The total target reduction for “Annex 1” (developed world) signatory countries to the Kyoto Protocol was 0.2 Gt per year.

Put bluntly, there is an absolutely gigantic pile of carbon-rich organic material just sitting up there in a freezer locker, lying at or very near the surface of the ground. The big question is, what will happen to that carbon as it thaws out? Will it stay put, perhaps even offsetting the greenhouse effect thanks to faster-growing plants, thus storing more carbon even faster than before? Or will the microbes wake up and chow down, feasting on thousands of years of accumulated compost and farting voluminous quantities of methane and carbon dioxide back into the air? I’m not suggesting that sixteen hundred gigatons of deeply frozen soil carbon could all be returned to the atmosphere at once, but even 5% or 10% of it would be enormous.

This possibility is another one of those climate genies that we are only just beginning to assess. Compared with the previous two, relatively little work has been done on it. Most permafrost research has traditionally focused on engineering, i.e., how to build structures without thawing the ground, thus slumping it and destroying what was built. Hardly anyone cared much about permafrost carbon until recently.

We don’t know how quickly or deeply permafrost will thaw or how quickly and deeply the microbes will get to work. The microbes themselves generate heat, and we’re not sure how much this will further enhance the permafrost thawing process. The net outcome—net carbon storage versus net carbon release—hinges on a small difference between two far larger and opposed numbers (i.e., the rates of plant primary production versus microbial decomposition). Both numbers are difficult to measure and have large uncertainties associated with them.

Much also depends on hydrology. The millions of lakes sprinkled across permafrost landscapes are themselves heavy greenhouse gas emitters and even bubble forth with pure methane, so their fate, too, is intimately tied to our climate future. Also, if thawed permafrost soils become dry and aerated (as might be expected if deep permafrost goes away), then microbes will release stored carbon in the form of carbon dioxide. If soils stay wet (as might be expected from climate model predictions of increased northern precipitation), then microbes will release it as methane, which is twenty-five times more potent a greenhouse gas than carbon dioxide.