by Curt Stager
For some people in that far future who have enough of a sense of history to realize what’s happening, these inexorable changes may be a source of unease. Others revel in the dramatic. If an active media industry still exists in 10,000 AD, headlines may warn that “Global Cooling Threatens Greenland with Icy Doom.” Newscasters may try to boost ratings by describing in lurid detail how colder weather increases the risk of death by exposure and ice-related injuries, and the term “carbon crisis” might be used in reference to a shortage, rather than an excess, of greenhouse gases. Some who notice the changes might yearn for the slightly warmer, greener, gentler settings that their grandparents grew up in, as Norse homesteaders probably did while encroaching sea ice slowly locked them away from the rest of the world at the close of the temporary warm period that had brought Eirik there centuries earlier.
And some day much farther down the carbon curve, the rebounding crust that once cradled the shrinking waters of Ny Fjord Lake will rise high enough to tip the last of them into the Atlantic. One can only guess when that might be; perhaps in 50,000 AD. Greenland’s vertical profile will have oscillated from a dome of ice to a sunken bowl of water to a rising dome of stone. The forested, farmed, and settled landscape will slope upward from west to east, and rivers will rush seaward down formerly ice-bound valleys to drain a rugged spine of mountains on the eastern rim of the great island. It is those mountainous highlands that will eventually spawn a new, ground-crushing ice encroachment when our carbon legacy finally fades to insignificance.
Greenland probably wins more than it loses in this long view of the future, even though it can’t keep Ny Fjord in the end. Meanwhile, tiny Denmark shrinks as the sea rises. By the time Greenland loses all of its ice in an extreme-emissions scenario, additional losses from Antarctica could contribute to a total sea-level rise of 40 feet (12 m) or more, enough to submerge the large, flat Danish island of Lolland and nearly sever the Jutland peninsula from mainland Europe. With that future in mind, it’s all the more interesting to watch Denmark now loosen its former grip on Greenland, one of the few places that’s likely to benefit substantially from global warming. By doing so, it might be letting go of a future lifeline.
When Greenland gained home rule within the Danish Commonwealth in 1979, the Home Rule Parliament left Denmark in charge of foreign policy, defense, currency issues, and the judicial system. Pressure is now growing amid Greenland’s mix of 50,000 Inuit and 6,000 Danes to further increase their national autonomy, and in November 2008, local voters passed a nonbinding referendum on full independence. From their local perspective, Anthropocene warming may increasingly favor complete separation, especially once the Arctic Ocean becomes ice-free, more vegetation begins to thrive, and the shrinking ice sheet exposes more and more of Greenland’s hidden treasures.
With Denmark’s long-term survival at stake, the Danes will have strong incentives to try to convince their old friends to remain within the fold or, at least, to remain friends. Sooner or later, they’re going to need Greenland much more than Greenland needs them.
10
What About the Tropics?
Essentially, all models are wrong, but some
are useful.
—George Box, statistician
Pale wisps of white quartz sand slither and hiss as a hot wind sweeps them across the hard-packed floor of what was once Ferguson’s Gulf. The broad, shallow bay had dimpled the western shore of Lake Turkana, an emerald-tinted sea of alkaline water nearly 180 miles (290 km) long that glistens in the harsh, nearly roadless desert of northern Kenya. A sun-roasted spit of fine sand and coarse, spiny scrub circles the desiccated bay like an arm reaching out from the mainland to cradle a basket. A basket that once held fish, and lots of them.
On this day in 1988, Ferguson’s Gulf holds little more than camel droppings and the sandal prints of Turkana nomads. A jetty that once stretched hundreds of yards from the gently sloping shore to reach boat-friendly depths is now a skeleton of rusted iron pilings, its boards long since scavenged and burned for firewood. A short distance farther inland, a large building that resembles an airplane hangar stands empty, the wind moaning through holes in the sheet metal shell. During the late 1970s Norway spent millions of dollars to build this fish refrigeration and processing plant, hoping that it would help to coax skeptical herders of cattle and goats to settle and net the huge Nile perch and other fish that spawned in the jade green shallows of the lake. The aim was to lift the Turkana people out of poverty and drought sensitivity into the supposedly stable money economy of modern times.
Very quickly, things went wrong. The cost of cooling the enormous building in the fierce desert heat outweighed any profits the filets provided. And the reluctant Turkana, who had traditionally shunned fish as a starvation food, owned no boats for deepwater fishing. Instead, they harvested the gulf as if it were an aquaculture pond. Its flat bottom let them wade neck deep in the murky waters, towing handheld nets and baited lines behind them. Crocodiles pursued the same fish in the same place, often cruising uncomfortably close to the fishermen. Sometimes, unwary children became their prey instead. Meanwhile, newly sedentary livestock nibbled the already sparse, mostly thorny vegetation bare in an ever-widening ring around the settlement, further locking their owners into an increasingly tenuous, lake-based lifestyle.
And then the lake level began to fall. Ferguson’s Gulf shrank, then fused with the surrounding sands, leaving the Turkana bereft of their primary fishing grounds. Many headed back into the hills to escape the overgrazed zone with what remained of their herds. Apparently, the project planning team forgot or failed to recognize that lake levels can change, and that Lake Turkana’s surface has a long history of doing so. An expert who was later sent from Norway to evaluate the defunct fish-factory-in-the-desert ruefully summed it up with the question: “How could we have been so stupid?”
Jetty leading into the center of Ferguson s Gulf, Lake Turkana, Kenya, before and after the lake level fell; top photo taken in 1981, bottom photo taken in 3:988. Curt Stager
In hindsight, it can be easy to dismiss this story as just another interventionist boondoggle, and it seemed like one to me as I drove across Ferguson’s Gulf seven years after boating on it in 1981 and having seen the short-lived fishery while it was still in operation. But such mistakes are in fact easy to make. The trap is readily reset when well-meaning people try to help others without fully understanding their physical and cultural settings. Nowadays, with threats of impending climate change urging people to reach into their wallets or policy manuals on behalf of developing tropical nations, it’s all too easy to overlook one troublesome fact. Tropical climates are among the least understood of any on the planet. How can we prepare effectively for coming changes if we don’t know exactly what is going to happen?
In the latest IPCC assessment report, the tropics received less attention than higher latitudes and the world as a whole in the overviews and predictions for the twenty-first century. That was not because the tropics are unimportant; they cover two-fifths of Earth’s surface and support roughly half of all humanity. Some say that this kind of imbalance occurs because most climate research originates in extratropical nations, and it tends to focus more often on northern winter and summer conditions than on the “offseason” months when most equatorial rains fall. Others add that precipitation patterns are generally more important in the tropics than temperature variations are, but rainfall can be difficult for computers to model and forecast accurately. And most experts agree that we have less background information to work with when we study tropical climates than when we consider those in North America or Europe. The United States, for example, has a well-funded, frequently updated, and easily accessible online repository of high-quality weather station data called the U.S. Historical Climatology Network (USHCN). No such network exists for most of the underserved and underrepresented tropics.
For some of us it may seem odd to imagine the greenhouse effect posing a threat to places that are alre
ady hot. But if we’re to understand climate change on a global scale, we have to know what is going on at the planet’s midriff as well as in its cooler places. To do otherwise is to risk repeating the errors that are humorously but effectively described in an old Indian folk tale that I enjoyed as a child. In that story, each of several blind men briefly touched different parts of a large elephant and then offered a seemingly reasonable but wildly inaccurate assessment of what the beast actually was. The man who touched the trunk concluded that the elephant was like a snake, the one who felt a massive rough-skinned leg called it a tree, another man who leaned against the beast’s broad flank thought it was a wall, and so on. In hopes of sketching a more complete picture of global climate change than that misguided group might produce, I’ll focus mainly on Africa and Peru where most of my research has been centered, while keeping in mind that much remains to be learned about how tropical weather works and what it will be like in the future.
Consider the situation for tropical Africa, which is typical of most other low-latitude regions, as well. The 2001 IPCC assessment reported that “deriving regional climate change predictions [is currently] impossible,” and “the potential effect of climate change on drought in Africa is uncertain.” The 2007 IPCC report cautioned against “the over-interpretation of results, owing to the limitations of some of the projections and models used,” and said that although droughts have long ravaged northern and eastern Africa, “it has not been demonstrated that these droughts can be simulated with coupled ocean-atmosphere models.” Tropical climatologist Richard Washington was recently quoted in Nature as saying, “You can get any result you like” with an African climate model. And an exhaustive review of regional simulations posted online by the Royal Netherlands Meteorological Institute (KNMI) shows a confusingly diverse range of possible hydrological futures for various subsections of the continent.
Because of this complexity and uncertainty, much of what you may read and hear about the future of tropical climate is questionable. In 2006, for example, an article in The Independent said that Africa will warm faster than the rest of the world and will face “the greatest catastrophe in human history,” citing economist Sir Nick Stern and various computer-model projections of West African droughts to support the claim. In contrast, a recent scientific report entitled The Copenhagen Diagnosis used similar models to show, as most sources do, that it is the poles, not the tropics that are warming fastest, and they also concluded that wetter conditions may occur in the West African Sahel, representing “a rare example of a positive tipping point” in response to global warming. Such contradictory predictions, along with the widely divergent model readouts on the KNMI website, suggest that deciding which vision of the near future to trust is more of a gamble than one might wish. And the same situation exists in other tropical regions as well; according to geophysicist Venkatachalam Ramaswamy in a recent issue of Eos, the climatology of Asia remains troubled by “insufficient understanding of intermodel differences” and “inadequacy of our climate models to resolve [regional] spatial scales.” Fortunately, sound scientific footing in that regard does exist, and much can simply be deduced from the basic nature of temperature and precipitation in the tropics.
Temperatures are already rising in the lower latitudes, though generally less so than in the polar regions where an extra thermal boost from the loss of reflective snow and ice is currently making them heat up faster than the global average. But people have lived longer in the warm tropics than anywhere else on Earth; we evolved there, after all. Life has survived abundantly in hot places for hundreds of millions of years, and it still thrives there today more than anywhere else. If you want to see thousands of species of frogs, fishes, flowers, and fungi, you go to the Amazon, not the Yukon.
In this context, it may seem odd that most of the imagery that we associate with global warming makes hot climates seem frightening, even deadly. Images of planets on fire or sweaty, red-faced Earths with thermometers sticking out of their mouths are good for gaining attention or raising money but less so for supporting well-informed discussions. Warming is indeed a problem, especially to organisms and societies that are adapted to stable or cooler conditions, but high temperatures themselves are not necessarily a deadly threat to those for whom they are already normal.
As the world warms, most tropical locales will not face the physical tipping point that amplifies changes at high latitudes and altitudes: namely, the melting temperature of ice. In places where things now freeze on a regular basis, future heating may have abrupt and dramatic physical effects from the collapse of ice sheets to the unsheathing of polar seas. But in already hot places there is no obvious ecological boundary to cross on a rising temperature curve. In the Arctic, it warms and warms and then suddenly there’s no ice for walruses to haul out on between dives, and the shift from snow cover to heat-absorbent soils, rocks, and vegetation drives temperatures radically higher. When the weather heats up further in most of the tropics, it mainly just feels that much warmer.
I’m sure that most residents of hot places would prefer not to see temperatures rise further. But as we weigh the human costs and benefits of a changing future, it’s worth remembering how Homo sapiens copes with heat in more realistic terms than those we often encounter in the mainstream media.
I’ll never forget gaping in amazement as columns of muscular French Foreign Legionnaires jogged and maneuvered amid the rippling mirages of Djibouti, a furnacelike pocket of lava ridges and troughs that notches the Horn of Africa between Ethiopia and Somalia. The hammering sun and thick, humid air intimidated me as a newcomer, and shortly before I arrived, a carload of French tourists died of heat stroke within hours of a breakdown on a remote desert road. However, off-duty legionnaires later told me that they eventually acclimatize enough to do what has to be done outdoors, regardless of the heat. And after hours, the streets of the capital are alive with off-duty soldiers and local folks because it becomes quite a bit cooler there after sundown. Even in the torrid outback of Djibouti, people love the land that they were born into, and generations of pastoral nomads have vigorously defended their claims to that harshly beautiful landscape from others who have sought to take it for themselves.
These examples show that high temperatures are not necessarily intolerable, especially if one is used to them and not also suffering from extreme poverty, disease, or war on top of everything else. It is mainly change itself that threatens life as we know it more than any particular thermal set point, and the global cooling that eventually follows the future climate whiplash period will also cause problems for many of our descendants, just as the opposite trends do now.
Misunderstandings of tropical climate history are also common. One of the most surprising geological discoveries of the nineteenth century was the realization that vast ice sheets have repeatedly covered much of Eurasia and North America during the last 2 to 3 million years. With the legacy of those past coolings in mind, many scientists assumed from the shortage of glacial landforms in the tropics that low-latitude climates have always been stable, and that the high biodiversity of the tropics reflects a benign climatic setting. But those assumptions are wrong.
What “temperate zoners” often fail to realize is that climate involves more than just temperature alone. I grew up in New England believing that seasons are either cold or warm, and that major climatic shifts of the past centered on the advance or retreat of ice sheets. But if I had grown up in Nairobi or Jakarta, the main seasons would be either wet or dry, and the most noteworthy weather-related disturbances in local history would have involved flooding or drought. Precipitation is just as much a factor in global climate change as temperature is, and in most of the tropics it is by far the more important of the two. Unfortunately, it is also more difficult to model and predict.
Scientists have only known much about the central roles of rainfall and drought in the long-term ecological history of the tropics for the last half century or so, since paleoecologists began to anal
yze sediment cores from tropical sites. Among the first was my graduate advisor at Duke University, Dan Livingstone, who traveled through much of East Africa with his graduate students during the 1960s in order to study vegetation and lake levels of the past as a way of deciphering the nature and causes of tropical climate variability.
Using now-classic techniques, Livingstone and his students drove long metal pipes into the soft sediments beneath lakes such as Victoria, Tanganyika, and Cheshi (where a crocodile sank their boat but let them escape). Back in the lab, they studied ancient pollen grains and the glassy shells of diatom algae under the microscope and reconstructed, layer by sedimentary layer, a record of African climate that stretched thousands of years into the past. What they found surprised the scientific community. Not only had ice ages brought climatic changes to the tropics after all; the paleoclimate records showed that those changes were both extreme and quite different from those at high latitudes.
When the north grew colder and snowier East Africa cooled somewhat as well, but instead of becoming wetter, it parched. Near the end of the last ice age, East Africa became so dry that local forests gave way to dry savannas. About 17,000 to 16,000 years ago, the surface of 4,800-foot-deep (1,470 m) Lake Tanganyika sank low within its Rift Valley basin, and Victoria, now the world’s largest tropical lake, disappeared altogether. Elsewhere in the presently wet monsoonal regions of southern Asia, geohistorical investigations reveal similarly intense drying, as well. The changes made physical sense, after all; warmth drives humid air upward where it condenses into rain clouds, and cooling tends to reverse the pattern. Paleoclimate records have repeatedly shown that this basic rule of thumb—warming means wetter, cooling means drier—applies to long-term climatic history in much of the inner tropics. This, in turn, eliminates environmental stability as a possible cause for high species diversity in the tropics, and the mystery still remains unsolved in scientific circles.