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

like flipping a switch. The implications of this are global, as we shall see next.

The Pentagon Report

From a societal perspective, an abrupt unexpected climate change is more destabilizing than one that is gradual and anticipated. Military analysts concede that the expected gradual climate changes pose national security threats, and by late 2009 the U.S. Central Intelligence Agency had opened a new center specifically dedicated to assessing them.⁴⁹³ A recent study, for example, projects a more than 50% increase in armed conflict and nearly four hundred thousand more battle deaths in Africa by 2030.⁴⁹⁴ But one of the few attempts to assess the societal impact of an abrupt climate change was commissioned by the U.S. Department of Defense in 2003.

This document, titled “An Abrupt Climate Change Scenario and Its Implications for United States National Security,” is not based on climate model projections, but instead on a known prehistoric event seen in ice cores, sediments, and fossils. About 8,200 years ago, several thousand years after the really big swings that Alley had studied, temperatures near Greenland suddenly tumbled by about 6°-7°C. Cold, dry, windy conditions spread across northern Europe and into Asia; certain African and Asian monsoon rains faltered, and temperatures probably rose slightly around the southern hemisphere. These conditions persisted for about 160 years before reversing again.

This event was not unique but simply the last and smallest of several climate shudders seen in Greenland ice cores as the last ice age wound down. It was less severe, shorter-lived, and less geographically extensive than its predecessors (especially the Younger Dryas event, the monster cold snap studied by Alley that abruptly kicked in about 12,700 years ago, then persisted for nearly 1,300 years).⁴⁹⁵ That said, let’s hope that it never happens again. The Pentagon’s report, which outlines possible social scenarios if what occurred 8,200 years ago were to happen again today, is quite scary.

It describes wars, starvation, disease, refugee flows, a human population crash, civil war in China, and the defensive fortification of the United States and Australia. “While the U.S. itself will be relatively better off and with more adaptive capacity,” the authors conclude, “it will find itself in a world where Europe will be struggling internally, large numbers of refugees washing up on its shores, and Asia in serious crisis over food and water. Disruption and conflict will be endemic features of life.”⁴⁹⁶ The report’s authors insist that their assessment, while extreme, is plausible.

Could this really happen? Nobody knows for certain, but the good news is that the physical mechanism underlying these North Atlantic cold shudders is now fairly well understood, and its behavior successfully replicated by climate models, so we can at least test the probability. The culprit appears to be a slowdown of the global thermohaline circulation—the long, ribbon-like “heat conveyor belt” of ocean currents, one arm of which carries warm tropical water from the Indian Ocean all the way to the Nordic seas, bathing western Europe and Scandinavia in all that heat so undeserved for its latitude as described in Chapter 7. The North Atlantic region is a critical pivot for this global circulation pattern. It is where the warm, salty north-flowing surface current finally cools sufficiently so that it becomes heavier than the surrounding colder (but less saline) water, sinks down to the ocean floor, and begins its millennia-long return south, crawling along the dark bottom of the abyss.

All of this is driven by density contrasts. If sufficiently large, a local freshening of the North Atlantic can slow or even halt the sinking, thus killing this entire overturning arm of the global heat conveyor belt. This has immediate implications for the Earth’s climate. Heat becomes less mixed around the planet. Cold temperatures (especially winters) and drought descend upon Europe. The southern latitudes warm; the Asian and African monsoons weaken or drift. It’s rather like adding hot water to a cold bath, in which stirring the water around helps to even out the temperature contrasts. But with no water circulation, one’s back grows cold but feet are scalded.

The most likely source of water for the sudden freshening of the North Atlantic was one or more massive floods released from the North American continent at the end of the last ice age, as its giant glacial ice sheet melted away. As the sheet retreated north into Canada, huge freshwater lakes, some even larger than the Great Lakes today, pooled against its shrinking edge. Then, when a pathway to the sea emerged from beneath the rotting ice, out the water went. The deluge that tore out through Hudson Bay must have been biblically awesome in scale.⁴⁹⁷ I wonder if any aboriginal version of Noah witnessed and survived it, creating a legend for generations of the Great Flood that drained the Earth’s water to the sea, bringing seemingly endless winter upon the land.

Figuring out hidden genies takes time and a lot of work. The above hydrologic explanation for the North Atlantic climate shudders was first proposed by Columbia University’s Wallace Broecker back in 1985.⁴⁹⁸ Its finer details are still being tinkered with today. But now that we understand this genie rather well, and its physics are reproducible in climate models, we can assess the likelihood of another such shudder happening again in the future.

So far, most simulations agree that a complete collapse of the thermohaline circulation is unlikely anytime soon, for the simple reason that it’s hard to find a big enough freshwater source with which to sufficiently hose down the North Atlantic. The Laurentide ice sheet that once covered Canada and much of the American Midwest is long gone. The projected increases in high-latitude precipitation and river runoff appear sufficient to weaken the circulation, but not enough to kill it outright.⁴⁹⁹ This weakening shows up in most future climate model projections as a little bull’s-eye of below-average warming centered over the North Atlantic. It’s not enough to create outright cooling, but it does reduce the magnitude of warming locally over this area. Let’s hope these simulations are correct—because if they’re wrong, losing even part of the Asian monsoon would be really, really bad.

There is, of course, another big source of potential freshwater—one that happens to be plunked right in the middle of the North Atlantic. No serious scientist thinks the Greenland Ice Sheet will melt away anytime soon, and if it ever does we’ll be dealing with even bigger worldwide problems than a cold, dry Europe and faltering monsoonal rains. But this genie, we’re nowhere near to understanding well enough to model yet.

Genie in the Ice

Two smelly straight guys sharing a tent sized for one is bad enough. But waking up covered in yellow dust, with no hot water for days, is the pits. It was impossible to keep the stuff out, even barricaded inside the lone wind-rated tent we had thought to bring with us.

The Greenland Ice Sheet was in charge, not me and not Ohio State geography professor Jason Box. We were camped next to its southwestern edge, where one of its many outlet glaciers finally succumbs to a grinding wet death, killed by the sun among the tundra grasses, caribou, and musk oxen. Every night, we squeezed head- to-toe in the little tent and buttoned up tight. Every night a fierce katabatic wind would pour off the ice sheet, lift tons of grit from its gravelly outwash plain, and fling it against our shuddering tent. The silt pushed through closed zippers and tiny mesh slits. It entered our nostrils and encrusted our hands as they gripped the tent’s violently shaking poles.

But by morning the winds would die down and we went to work. Jason installed time-lapse cameras to track the speed of the glacier’s sliding snout; I submerged electronic sensors in its outgoing torrent of meltwater to monitor how much was flowing off to the sea. We were studying these things to help answer a burning scientific question that should worry us all. Chapter 4 showed that we are facing decimeters of sea-level rise by century’s end. Many scientists wonder if even these estimates might be too low. Could climate warming cause the Greenland and West Antarctic ice sheets to accelerate their dumpage of ice and water into the sea, thus cranking up its rise even faster than is happening already? Could the world’s oceans go even higher, say a couple of meters by the end of this century?

The short answer is maybe. The geological record tells us sea levels are certainly capable of responding quickly to shrinking glaciers. And over the long haul—meaning several thousands of years—it looks like the Greenland Ice Sheet is in trouble and could well disappear completely.⁵⁰⁰ Glaciers and ice sheets are