Deep Future

by Curt Stager

  Secondly, although most models indicate wetter conditions in the region by 2100 AD, most of Peru’s mountains are currently undergoing a drying trend that might last for several more decades, and that drying process can affect local wetlands as much as it does glaciers. Drought among the bofedales could therefore threaten alpine pastoralists and their alpaca herds as well as lowland farms and settlements, and an unpleasant combination of warming and drying might drive some people out of the highlands altogether.

  In any system shift that is as all-encompassing as global climate change, there will be winners as well as losers, and the future of the low latitudes need not be totally grim. As Hadley circulation speeds up, for example, the ITCZ should drop more rain on most of the tropics. In some situations, heavy rains can be troublesome because they wash roads and bridges away, erode topsoil, and leave puddles for disease-bearing insects to breed in. But rain is also a valuable commodity in seasonally dry regions, particularly in nations that rely heavily upon agriculture and hydro power for subsistence and commerce.

  Most Pakistani farmers or Indonesian rice-paddy harvesters are less likely to bemoan the arrival of heavy summer monsoons than to worry that the rains may weaken or fail on occasion. According to most global circulation models, however, the vast monsoonal regions of southern Asia will become wetter as the tropical atmosphere and oceans warm. More copious rains could also help to keep a sizable fraction of Amazonian rain forests green, and increased precipitation in the Andes later in this century might help to keep some ice and snow on the peaks there. Wetter conditions in the East African headwaters of the Nile could open new areas along the river’s green flanks in lowland Sudan and Egypt for irrigation and settlement. Subsistence farming keeps many Kenyans and Tanzanians fed today, and just as the last bits of arable land are coming under the hoe we learn that more abundant and reliable rains—and fewer killing frosts at higher elevations—may be coming. Many who stand to benefit thus from such changes are among the world’s least wealthy, and the possibility that warming might in some cases improve their lives should be considered seriously in any tally of the costs and benefits of Anthropocene climate change.

  Unfortunately, such conclusions are difficult to make with perfect certainty. One can reasonably assume that warming should stimulate Hadley circulation and use that assumption as the basis for drawing rough maps of future wet and dry zones even without the aid of computer models. But again, the story may be more complex than it seems at first. Take cyclones, for example. In theory, warming should increase their frequency and strength, but despite well-documented heating trends in the lower latitudes there is blessedly little evidence (yet) for thermally enhanced cyclone activity in most of the topics. The same cannot be said for Atlantic hurricanes, though; several studies do indicate a significant increase in hurricane activity since the 1970s and 1980s that may be due, at least in part, to oceanic warming.

  The uncertainty runs deeper still, because inherent variability in the Hadley cells and ITCZ are not the only players in the field of tropical rainfall dynamics. For reasons unknown even to solar physicists, the sun releases slightly more energy than usual every eleven years or so, and a growing body of evidence suggests that those mild fluctuations can sometimes influence weather on Earth. In 2007, my colleagues and I published a paper in the Journal of Geophysical Research showing that those small oscillations in the strength of the sun’s output appear to trigger unusually heavy precipitation in East Africa, and that such rhythmic, rainfall-driven pulses occurred in the levels of Rift Valley lakes throughout the twentieth century. Similar decadal rainfall pulses have also been found in parts of southern Africa, only in reverse; there, the mild solar energy peaks are linked to droughts.

  The effects of the equatorial rainfall pulses are complex, and not all of them are desirable. More rain can mean more water for crops and reservoirs, but it also spreads disease by creating puddles for mosquitoes to breed in. With clockwork regularity, episodes of unusually heavy rain have triggered major outbreaks of Rift Valley fever in Kenya since detailed record keeping began in the 1950s. Unfortunately, exactly how this apparent sun-weather linkage works is still unclear—most likely it is related to surface temperatures in the Indian Ocean—and to my knowledge no climate models have reproduced it yet.

  But there is yet another source of tropical rainfall variation to consider, one that links the weather of Africa to that of Peru and other locations around the world. Its influence is more widely felt than the effects of the solar cycle, but its pacing is far less predictable and we know less about it than we should if we are to plan effectively for a warmer tropical future. That wild card is El Niño.

  Shortly before global warming invaded the world’s newsstands a decade or so ago, El Niño was the dominant climatic star on stage. If you’re old enough, you might remember when it first drew extensive media coverage outside of South America, back in 1983 when one of the most powerful El Niño events on record threw weather systems around the globe into disarray. Perhaps it was the intensity of that disturbance, which drenched the southern United States and desiccated islands of the western Pacific, that first attracted world attention to what was previously treated like a quaintly localized phenomenon. Perhaps it was also the writings of prominent scientists who happened to be monitoring Peru’s coastal upwelling system when the sudden slackening of winds shut it down. Whatever the reason, many of us are now more or less familiar with the term itself, which refers to the climatic disturbances whose onsets approximately coincide with December, the traditional birth date of the Christ child, usually every three to seven years or so.

  El Niño begins with a slackening of easterly winds, which slows the upwelling of deep, cold waters along the coasts of Peru and Ecuador. As the sea warms, air moistens with marine water vapor and heats up enough to rise and condense into rain clouds. The effects of that regional switch from desert to deluge cascade through sensitive sites around the world, generally making the weather wetter in places that are normally somewhat dry (Kenya, Texas) and drier in the wet places (Queensland, Zimbabwe). In 1997–1998, when another severe Niño drought struck Indonesia, dehydrated peatlands caught fire and smoldered for months, choking everything from Jogjakarta to Singapore with lung-searing smoke. As much as a third of Indonesia’s wild forest orangutans are thought to have died as a result of the flames and fumes, either directly or from forced migrations into dangerously unfamiliar or more heavily settled areas.

  Such changes in weather patterns could be powerful enough to complicate expected rainfall trends in much of the tropics. But despite El Niño’s huge influence on climates worldwide, we’re still not sure what has been causing it since the modern version of it began, roughly 5,000 to 7,000 years ago, much less what it may do during the rest of the Anthropocene. Not surprisingly, computer projections about the coming responses of El Niño to rising temperatures vary a great deal. In a paper published in 2005, British climatologist Matthew Collins and a team representing sixteen international research groups reported that models in which the El Niño system changed the most also produced the least reliable simulations, and they concluded that no major disruptions of that system are likely to occur as a result of future warming.

  Geologic history also paints a rather blurred picture in this case. Sediment cores from the Galápagos Islands, the Ecuadorian mountains, and marine deposits off the Peruvian coast contain abundant evidence of past El Niño floods, but the records that we currently have on hand still leave much unexplained. Most of them do suggest that a long-term suppression of El Niño activity occurred during northern summer warmings 7,000 to 10,000 or so years ago, but that change was due to factors other than human-produced greenhouse gases, and some of them offer conflicting versions of rainfall conditions during warm and cool phases of the last millennium. Furthermore, the prolonged global warmth of the Eocene epoch 34 to 55 million years ago caused little or no change in El Niño activity, at least none that has left convincing signs in published geo
historical records. This unfortunate situation leaves us largely ignorant of what El Niño will do to tropical rains in the future as we move along the rising and falling curve of fossil carbon emissions.

  Although we can’t be sure exactly how Hadley cells, El Niño, and related weather systems may respond as global average temperature rises, we can still be fairly certain that changes are imminent, if not already under way, and that some of them could be severe. With this in mind, we may pity official decision makers in tropical nations who hear the warning cry to “Look out!” as they struggle to see what lies ahead. A recent editorial in Nature described that situation at a conference in Johannesburg in 2005. A gathering of more than fifty foreign researchers warned government officials and planners that they need to “take urgent action” in the face of global warming, and said that “the key is to convert these concerns into action.” But none of those experts explained what that action should be. How can you respond appropriately when you don’t know what you’re supposed to respond to?

  It is often said that inaction in the face of impending climate change is not an option, but choosing the wrong response can be dangerous, too. In 1997, for example, meteorologists used sophisticated computer models to warn that a severe El Niño-induced drought was about to strike southern Africa. As a result many local farmers held off on planting crops that seemed to be doomed to failure, but the rains fell almost as abundantly as usual despite the forecast. When the nation’s food supplies shrank in response to the farm cutbacks, people’s trust in the meteorologists shriveled, too. That, in turn, caused a second wave of damage when resentful citizens later ignored subsequent warnings of impending floods, which actually did appear as predicted and killed hundreds of people in the region.

  Rather than try to predict specific climatic changes with great precision—which many scientists believe is impossible even with the most sophisticated models—an increasing number of experts favor preparatory strategies that enhance general adaptability in anticipation of a wide range of possible futures. That approach typically involves building resilience by addressing vulnerabilities in aspects of life that are more immediately troublesome than global warming, such as poverty, disease, war, and limited access to education and technology. If you’re well off financially and socially, then it doesn’t matter so much what the weather is like; the example of oil-rich Dubai, on the Persian Gulf, shows that one can theoretically enjoy a comfortable lifestyle even in a barren sun-baked landscape where summer air temperatures exceed 106°F (41°C). It is mainly low incomes, societal instability, and inadequate infrastructure that make climatic change of any kind such a threat to so many residents of the tropics. Though some activists claim that adaptation is a cop-out, that all efforts should be concentrated on reducing carbon emissions as the root of the problem, I find it difficult to justify that attitude in the case of tropical nations. These include some of the world’s least resilient cultures and economies, and they have made the smallest contributions to planetary heating in the first place. It is particularly important for them to maintain stable, well-balanced stances while walking into a poorly understood climatic future so they can react quickly and effectively to unforeseen obstacles in their path.

  In that spirit, the following advice may be helpful: focus on the long term. Don’t fall for illusions of stability or miragelike trends that can appear on short-term horizons. Remember those misguided blind men for whom the cursory feel of an elephant’s leg, trunk, or flank made the creature before them seem to be a tree, a snake, or a wall; incomplete information can fool us into making dangerously inaccurate conclusions about the world we live in.

  In much of Peru, for example, the accelerated melting of mountain glaciers is now sending extra meltwater downhill to thirsty farms, towns, and power dams, but the surplus will likely reverse into a deficit as the ice shrinks further, probably within the next few decades. Adapting to this temporary bonanza by boosting demand could therefore be disastrous in the long run. Better to concentrate now on conserving high wetlands and on building more reservoirs and canals, keeping a wary eye on a drier future (as well as on earthquake-resistant construction methods).

  In Africa, the desiccation of Ferguson’s Gulf need not have taken anybody by surprise if they had maintained a historical view of the place that was farsighted enough to recognize the full range of lake level variability. But a similar mistake is now being made in reports of a recent drying trend farther south in the Lake Victoria watershed. The level of that lake has been falling since the 1960s, which threatens to strand existing fishing boat launch sites farther and farther from the water’s edge and weaken the generative capacity of hydropower turbines on the Nile outlet. But this is probably not really a sign that global warming is sucking the lake basin dry. Charts of the full twentieth-century lake level record suggest that this short-term trend is part of a decades-long recovery from an as yet unexplained, unusually wet period that soaked tropical Africa between 1961 and 1964. In that case, it probably has little predictive value other than to serve as a reminder that tropical rainfall regimes can be extremely variable; if anything, the equatorial Victoria basin should eventually become wetter as it warms through the twenty-first century and beyond, not drier.

  A truly long-term view of climate also warns of another aspect of Anthropocene change that favors thoughtful flexibility rather than rigid, overly specific preparatory strategies. Many of the trends that are appearing around us now will eventually reverse. After thermal maximum passes and climate whiplash runs its course, inexorable global cooling should progressively slow the Hadley circulation down, thereby weakening monsoons in much of the tropics and lightening up on some of the aridity elsewhere. The crest of Peru’s snowy Cordillera Blanca may spend some time looking more like the “Cordillera Dry and Brown,” but then the increasingly frequent frostings that drop from alpine skies will take longer and longer to fade away, and they will hold the promise of heavier, more reliable snowmelts to come in the deep future.

  On the far, cooling side of the coming thermal divide there will be new environmental winners as well as losers, just as there are now. To paraphrase Bob Dylan, “the first ones now may later be last.” Best to keep our eyes open and focused far ahead because some of the chances available to us now for effective preparation and adaptation may not come again. Yes, tropical climates are changing, too; of that, and only that, we can be sure.

  11

  Bringing It Home

  Not all change is bad. Where a reasonably healthy, reasonably diverse ecosystem is providing at least some kind of service, we might be better off to embrace our altered Earth…. We may even learn

  to find some charm there.

  —Editorial, Nature, July 23, 2009

  Most of this book has been dedicated to the understanding of grand sweeps of time and planet-spanning environmental changes. But the events that it describes will be experienced by our descendants on much smaller, personal scales. Global averages of temperature and precipitation are constructed from individual data points, as a house is built from various boards and beams. Each component has a more or less unique shape and position, and the dimensions of any given handful of them can differ widely from the overall average. The computer models that illustrate global trends are too farsighted to focus easily on the little places where you and I and future generations must deal with climate up close. And in order to envision what greenhouse warming means for specific locales we need more place-based information to guide us.

  In this chapter, I’ll turn to the temperate zone for examples of what the Anthropocene may have in store for some of those little places that fall between the climatic extremes of the poles and the equator. At the highest latitudes, many of the most important ecological changes will involve the melting of ice, and in the tropics, rainfall variability will be the dominant theme. But in the middle latitudes, those that encompass the United States, central Eurasia, and the southerly portions of Canada, South America, Australia, New Zea
land, and Africa, the situation is rather more complex. In those regions, ice and snow are confined to higher elevations and to certain times of year, and precipitation or drought are rarely limited to any particular season.

  As a result of that geographical diversity, it can be more difficult to anticipate what Anthropocene warming means for a temperate-zone site than for the North Pole or humid equatorial Africa, other than a near-universal rise in mean annual temperatures. To do so with a reasonable amount of certainty requires intimate knowledge of the setting in question and an awareness of how changes in planetary-scale weather systems influence the small-scale locales that we actually live in. Such place-based familiarity is essential to understanding what global climate change means to one’s home turf, and in that spirit I’ll choose two such places here for illustrative purposes, the Cape Province of South Africa to represent the southern midlatitudes and upstate New York to represent the northern ones. I’ve selected these locales because I know them fairly well and because they represent two very different climatic regimes, with the African site being more vulnerable to coming changes in precipitation and the American one slated to be more directly affected by warming. But I’ll focus most closely on the latter region for one simple reason: I live there.

  It may seem odd to some of us that the southern tip of Africa lies in the temperate zone. In the austral autumn, brown leaves fall from the sycamore trees and crunch underfoot on the sidewalks of Cape Town. In winter, it often snows on the high rocky escarpments that loom over the vineyards of Paarl and Stellenbosch. For much of the year, many South Africans wear sweaters and pull knit caps down tight over their ears while most of the rest of the continent swelters in tropical heat. But when summer comes, the seasonal warmth is glorious and the long sandy beaches draw crowds of swimmers and sunbathers. In some ways the weather resembles that of the semiarid Mediterranean or Californian coasts, but one is quickly reminded of South Africa’s uniqueness when one looks closely at the native vegetation out in the open countryside.