Abrupt Climate Changeby Richard B

Abrupt Climate ChangeBy Richard B. Alley

n the Hollywood disaster thriller Inevitable, too, are the potential chal- The Day after Tomorrow, a climate lenges to humanity. Unexpected warm Winter temperatures catastrophe of ice age proportions spells may make certain regions more catches the world unprepared. Mil- hospitable, but they could magnify swel- plummeting six degrees lions of North Americans fl ee to tering conditions elsewhere. Cold snaps sunny Mexico as wolves stalk the could make winters numbingly harsh Celsius and sudden last few people huddled in freeze- and clog key navigation routes with ice. dried New York City. Tornadoes rav- Severe droughts could render once fertile droughts scorching I age California. Giant hailstones pound land agriculturally barren. These conse- farmland around the Tokyo. quences would be particularly tough to Are overwhelmingly abrupt climate bear because climate changes that oc- globe are not just the changes likely to happen anytime soon, cur suddenly often persist for centuries or did Fox Studios exaggerate wildly? or even thousands of years. Indeed, the stuff of scary movies. The answer to both questions appears collapses of some ancient societies—once to be yes. Most climate experts agree attributed to social, economic and politi- Such striking climate that we need not fear a full-fl edged ice cal forces—are now being blamed largely age in the coming decades. But sudden, on rapid shifts in climate. jumps have happened dramatic climate changes have struck The specter of abrupt climate change many times in the past, and they could has attracted serious scientifi c investiga- before—sometimes happen again. In fact, they are probably tion for more than a decade, but it has inevitable. only recently captured the interest of within a matter of years SLIM FILMS FILMS SLIM

COPYRIGHT 2004 SCIENTIFIC AMERICAN, INC. fi lmmakers, economists and policymak- other hand it achieved roughly half of Ice layers that trapped dust from Asia ers. Along with more attention comes the heating sustained since the peak of indicated the source of prevailing winds, increasing confusion about what trig- the last ice age—more than 10 degrees for instance. Investigators concluded gers such change and what the outcomes C—in a mere decade. That jump, which that the winds must have been calmer will be. Casual observers might suppose occurred about 11,500 years ago, is the during warm times because less wind- that quick switches would dwarf any ef- equivalent of Minneapolis or Moscow blown sea salt and ash from faraway fects of human-induced global warming, acquiring the relatively sultry conditions volcanoes accumulated in the ice. And which has been occurring gradually. But of Atlanta or Madrid. the list of clues goes on [see “Greenland new evidence indicates that global warm- Not only did the ice cores reveal what Ice Cores: Frozen in Time,” by Richard ing should be more of a worry than ever: happened in Greenland, but they also B. Alley and Michael L. Bender; Scien- it could actually be pushing the earth’s hinted at the situation in the rest of the tifi c American, February 1998]. climate faster toward sudden shifts. world. Researchers had hypothesized that Intense, abrupt warming episodes the 10-degree warming in the north was appeared more than 20 times in the Jumping Back and Forth part of a warming episode across a broad Greenland ice records. Within several scientists might never have swath of the Northern Hemisphere and hundreds or thousands of years after fully appreciated the climate’s ability to that this episode enhanced precipitation the start of a typical warm period, the lurch into a radically different state if not in that region and far beyond. In Green- climate reverted to slow cooling fol- for ice cores extracted from Greenland’s land itself, the thickness of the annual lowed by quick cooling over as short a Global warming should be more of a worry than ever: it could be pushing the earth’s climate faster toward sudden shifts. massive ice sheet in the early 1990s. ice layers showed that, indeed, snowfall time as a century. Then the pattern be- These colossal rods of ice—some three had doubled in a single year. Analyses of gan again with another warming that kilometers long—entomb a remarkably old air bubbles caught in the ice corrobo- might take only a few years. During the clear set of climate records spanning the rated the prediction of increased wetness most extreme cold conditions, icebergs past 110,000 years. Investigators can dis- in other areas. In particular, measure- strayed as far south as the coast of Por- tinguish annual layers in the ice cores and ments of methane in the bubbles indi- tugal. Lesser challenges probably drove date them using a variety of methods; the cated that this swamp gas was entering the Vikings out of Greenland during the composition of the ice itself reveals the the atmosphere 50 percent faster during most recent cold snap, called the Little temperature at which it formed. the intense warming than it had previ- Ice Age, which started around A.D. 1400 Such work has revealed a long his- ously. The methane most likely entered and lasted 500 years. tory of wild fl uctuations in climate— the atmosphere as wetlands fl ooded in Sharp warm-ups and cool-downs in long deep freezes alternating with brief the tropics and thawed up north. the north unfolded differently elsewhere warm spells. Central Greenland experi- The cores also contained evidence in the world, even though they may have enced cold snaps as extreme as six de- that helped scientists fi ll in other details shared a common cause. Cold, wet times grees Celsius in just a few years. On the about the environment at various times. in Greenland correlate with particularly cold, dry, windy conditions in Europe and North America; they also coincide Overview/Inevitable Surprises with anomalously warm weather in the ■ Most climate change policy discussions and research efforts center on South Atlantic and Antarctica. Investi- global warming. But another problem looms as well: climate has suddenly gators pieced together these regional his- fl ip-fl opped in the past and will surely do so again. tories from additional clues they found ■ A regional drought could, for instance, arrive one summer and stay for in the ice of high mountain glaciers, the decades, wiping out rich agricultural lands across Asia and North America; thickness of tree rings, and the types of weather patterns in Europe could shift in a matter of years, making that area’s pollen and shells preserved in ancient climate more like Siberia’s. mud at the bottoms of lakes and oceans, ■ Scientists cannot yet predict when such abrupt changes will occur, but most among other sources. climate experts warn that global warming and human activities may be The evidence also revealed that abrupt propelling the world faster toward sudden, long-lasting climate changes. shifts in rainfall have offered up challenges rivaling those produced by tem-

Abrupt climate change has marked the earth’s history for from Mexico’s Yucatán Peninsula record sudden and severe eons. Ice cores from Greenland, for instance, reveal that droughts (bottom left) because a diagnostic ratio of oxygen wild temperature swings (top left) punctuated the gradual isotopes in the shells shoots up when more water evaporates warming that brought the planet out of the last ice age starting from the lake than falls as rain. Societies have often suffered about 18,000 years ago. Fossil shells in lake sediments as a result of these rapid shifts (photographs).

Medieval Warm Period –30

–35 8,200-Year Event Little Ice Age

–40 End of Younger Dryas (degrees Celsius) (degrees –45 Start of ; Temperature in Central Greenland Greenland in Central Temperature Younger Dryas Viking settlement, now in ruins, was among those in Greenland abandoned during an –50 abrupt cold spell called the Little Ice Age. 15 10 5 0 Time (thousands of years ago)

Drier Collapse of Mayan

National Geophysical Data Center Data Geophysical National civilization ) bottom graph bottom ) bottom photo bottom Climate and Precipitation and Climate ) AND D. HODELL ET AL. (

Inferred from Oxygen Isotope Composition Isotope Oxygen from Inferred Mayan rain god (statue in foreground) top graph was apparently no match for the drought Wetter now widely blamed for the collapse of Mayan 7 6 5 4 3 2 1 0 civilization about 1,100 years ago. Time (thousands of years ago)

perature swings. Cold times in the north ciﬁ c occasionally have steered weather key driver of climate toward an invisible typically brought drought to Saharan patterns far enough to trigger surprise threshold. At the point that threshold Africa and India. About 5,000 years ago droughts, such as the one responsible for was crossed, the climate driver—and thus a sudden drying converted the Sahara the U.S. dust bowl of the 1930s. the climate as well—ﬂ ipped to a new and );FREELANCE CONSULTING SERVICES PTY LTD/CORBIS ( PTY LTD/CORBIS SERVICES CONSULTING );FREELANCE from a green landscape dotted with lakes different state and usually stayed there to the scorching, sandy desert it is today. Point of No Return for a long time [see box on next page].

top photo Two centuries of dryness about 1,100 be they warm spells, cold snaps Crossing a climate threshold is simi- years ago apparently contributed to the or prolonged droughts, the precipitous lar to ﬂ ipping a canoe. If you are sitting end of classic Mayan civilization in Mex- climate changes of the past all happened in a canoe on a lake and you lean gradu- ico and elsewhere in Central America. In for essentially the same reason. In each ally to one side, the canoe tips, too. You modern times, the El Niño phenomenon case, a gradual change in temperature are pushing the canoe toward a thresh- RUDY BRUEGGEMANN ( BRUEGGEMANN RUDY ELIZA JEWETT; SOURCES: M. STUIVER ET AL. AND K. CUFFEY ET AL. ( AL. ET CUFFEY K. AND AL. ET STUIVER M. SOURCES: JEWETT; ELIZA and other anomalies in the North Pa- or other physical condition pushed a old—the position after which the boat

www.sciam.com SCIENTIFIC AMERICAN 65 COPYRIGHT 2004 SCIENTIFIC AMERICAN, INC. CROSSING THE THRESHOLD Global warming alters ambient conditions little by little. But climate—with potentially challenging consequences to people even this kind of slow, steady change can push climate drivers, and societies. Once a climate driver crosses its so-called such as well-established ocean currents or patterns of rainfall, threshold, the changes that ensue could persist for millennia. to a critical point at which they lurch abruptly into a new and Many thresholds may still await discovery; here are three that different state. That switch brings with it an associated shift in scientists have identifi ed: CLIMATE DRIVER THRESHOLD CROSSING RESULTING CLIMATE SHIFT SOCIAL CONSEQUENCES Ocean currents in the North Atlantic Freshening of surface waters Temperatures plummet in Agriculture suffers in carry warmth northward from tropics, in the far north slows down the region, and climate in Europe regions around the world, keeping western Europe’s winters mild these currents, possibly and the eastern U.S. becomes and key navigation routes (see box on opposite page). stopping them altogether. more like Alaska’s. become clogged with ice. Rainwater that is recycled through A minor dry spell wilts or kills A potentially mild dry spell is Parched land can no longer plants (absorbed by their roots and too many plants, and recycled enhanced and prolonged into support crops; famine strikes returned to the air through evaporation rainfall disappears, reinforcing a severe drought. those who cannot trade for from their leaves) provides much of the the drying in a vicious cycle. the remaining grain in the precipitation in the world’s grain belts. world market. Currents in the Pacifi c Ocean determine Natural phenomena, such as El Niño, Weather patterns on adjacent Some croplands dry up major patterns of sea-surface cause subtle changes in sea-surface continents shift, triggering severe while other places incur temperature, which in turn control temperatures, although scientists storms or droughts where they damage from intense storms. regional weather patterns. are still not sure why. typically do not occur. can no longer stay upright. Lean a bit too tic can slow or shut off the conveyor, rocking the boat—by changing so many far, and the canoe overturns. shifting climate as a result. aspects of our world so rapidly. Particu- Threshold crossings caused history’s Diluted by water from the land, sea- larly worrisome are human-induced in- most extreme climate fl ips—and point water fl owing in from the south would creases in atmospheric concentrations to areas of particular concern for the fu- become less salty and thus less dense, of greenhouse gases, which are pro- ture. To explain the icy spells recorded in possibly to the point that it could freeze moting global warming [see “Defusing Greenland’s ice cores, for example, most into sea ice before it had a chance to sink. the Global Warming Time Bomb,” by scientists implicate altered behavior of With sinking stopped and the conveyor James Hansen; Scientifi c American, currents in the North Atlantic, which halted, rain and snow that fell in the March; www.sciam.com/ontheweb]. are a dominant factor in that region’s north could not be swept into the deep The United Nations–sanctioned long-term weather patterns. ocean and carried away. Instead they Intergovernmental Panel on Climate Eastern North America and Europe would accumulate on the sea surface and Change has predicted that average enjoy temperate conditions (like today’s) freshen the North Atlantic even more. global temperatures will rise 1.5 to 4.5 when salty Atlantic waters warmed by The conveyor then would stay quiet, leav- degrees C in the next 100 years. Many southern sunshine fl ow northward across ing nearby continents with climates more computer models that agree with this as- the equator. During far northern winters, like Siberia’s [see box on opposite page]. sessment also predict a slowdown of the the salty water arriving from the south North Atlantic conveyor. (As ironic as it becomes cold and dense enough to sink Chilling Warmth may sound, gradual warming could lead east and west of Greenland, after which eight thousand years have to a sudden cooling of many degrees.) it migrates southward along the seafl oor. passed since the last of the biggest Uncertainties abound, and although a Meanwhile, as the cooled water sinks, North Atlantic cold snaps. Could it be new ice age is not thought credible, the warm currents from the south flow that humans are actually “leaning” in resulting changes could be notably larg- northward to take its place. The sink- the right direction to avoid fl ipping the er than they were during the Little Ice ing water thereby drives what is called a climate’s canoe? Perhaps, but most cli- Age, when the Thames in London froze conveyor belt circulation that warms the mate experts suspect instead that we are and glaciers rumbled down the Alps. north and cools the south. Ice cores contain evidence that sud- RICHARD B. ALLEY is professor of geosciences at Pennsylvania State University and an as- den cold periods occurred after the sociate at the Earth System Science Center there. Since earning his Ph.D. in geology from North Atlantic became less salty, per- the University of Wisconsin–Madison in 1987, Alley has focused his work on understand- haps because freshwater lakes burst ing how glaciers and ice sheets record climate change, how their fl ow affects sea level, and through the walls of glaciers and found how they erode and deposit sediment. Alley has spent three fi eld seasons in Antarctica and their way to the sea. Researchers identify THE AUTHOR fi ve in Greenland. During those visits, he helped to harvest many of the key ice cores that this rush of freshwater as the fi rst phase are revealing the history of the earth’s climate over the past 110,000 years. In 2001 Alley of a critical threshold crossing because won the national Phi Beta Kappa Science Award for his nontechnical book The Two-Mile Time they know freshening the North Atlan- Machine, which details the results from a two-mile-long ice core from Greenland.

66 SCIENTIFIC AMERICAN NOVEMBER 2004 COPYRIGHT 2004 SCIENTIFIC AMERICAN, INC. MELTING TOWARD A COLD SNAP? As global warming continues to heat up the planet, many strongly inﬂ uences climate elsewhere in the world. A conveyor scientists fear that large pulses of freshwater melting off the shutdown—or even a signiﬁ cant slowdown—could cool the Greenland ice sheet and other frozen northern landmasses North Atlantic region even as global temperatures continue could obstruct the so-called North Atlantic conveyor, the to rise. Other challenging and abrupt climate changes would system of ocean currents that brings warmth to Europe and almost certainly result.

Prevailing CONVEYOR ON winds Salty ocean currents (red) Greenland ﬂ owing northward from the WET tropics warm prevailing TEMPERATE Europe TEMPERATE winds (large arrows) as they North blow eastward toward Europe. America The heat-bearing currents, SEASONAL which are dense, become Atlantic MONSOONS even denser as they lose Ocean heat to the atmosphere. South Africa Eventually the cold, America salty water becomes dense enough to sink near Greenland. It then Conveyor migrates southward along the seaﬂ oor (blue), COLD leaving a void that draws more warm water from the south to take its place.

RESULTING CLIMATE When the North Atlantic conveyor is active, temperate conditions with relatively warm winters enable rich agricultural production in much of Europe and North America. Seasonal monsoons fuel growing seasons in broad swaths of Africa and the Far East. Central Asia is wet, and Antarctica and the South Atlantic are typically cold.

Prevailing CONVEYOR OFF winds If too much freshwater enters the North Atlantic, it dilutes Freshwater runoff the salty currents from COLD, DRY, WINDY Europe COLD, DRY, WINDY DRY the south. Surface waters North Sea ice no longer become dense America enough to sink, no matter Atlantic how cold the water gets, Ocean and the conveyor shuts DRY down or slows. Prevailing South Africa winds now carry frigid air America eastward (large arrows). This cold trend could endure for decades or more—until southern waters become salty enough to overwhelm WARM the fresher water up north, restarting the conveyor in an enormous rush.

RESULTING CLIMATE As the conveyor grows quiet, winters become harsher in much of Europe and North America, and agriculture suffers. These regions, along with those that usually rely on seasonal monsoons, suffer from droughts sometimes enhanced by stronger winds. Central Asia gets drier, and many regions in the Southern Hemisphere become warmer than usual. DAVID FIERSTEINDAVID

www.sciam.com SCIENTIFIC AMERICAN 67 COPYRIGHT 2004 SCIENTIFIC AMERICAN, INC. Tricky Predictions o credible predictions of abrupt climate changes have spells or droughts or fl ooding at the locations and times that ever been issued—nor should you expect one anytime have been recorded in annual layers of ice and sediment. Some soon. That is because rapid changes are inherently more of them even do a decent job of simulating shifts in storm tracks, N wind patterns, seasonal precipitation and other fi ner details. diffi cult to forecast than global warming or other gradual changes. One major stumbling block has to do with the very nature But even if the models get the general nature of the of abrupt change. A rapid shift occurs when a slow but steady climate change right, they represent important parameters force, such as global warming, imperfectly. In particular, moves a crucial component of the abrupt changes of the the climate system past a point past were usually larger and of no easy return. Crossing such more widespread than the a threshold triggers a sudden models indicate. Most of them switch to a new state—much underestimate the amount of the way leaning over too far in moisture lost in the Sahara over a canoe suddenly dumps you in the past few thousand years, for the lake. Knowing exactly how example. The models also seem to far you can tip the canoe without have trouble simulating both the overturning is almost impossible, great warmth of the polar regions however, especially as wind and during the time of the dinosaurs waves rock the boat. Similarly, it and the extreme cold at the peak is exceedingly tough to recognize of the most recent ice age. The simplest reason for when an aspect of climate is BALANCING ACT: The earth typically experiences a given approaching a critical threshold. climate for millennia or more. Then, at a moment that is these mismatches may be that Researchers have attempted nearly impossible to predict, some aspect of the climate the models are typically less to gain insight into the factors system teeters too far to one side and global conditions sensitive than the climate is, that operate near a tipping point tumble into a starkly different state. perhaps because they omit key through computer modeling. These efforts have revealed much feedbacks and responses. Climate thresholds that no one has about what rocks the climate’s canoe, but uncertainties still yet considered might also explain the discrepancies. Locating abound. To determine how accurately their computer models these thresholds would undoubtedly prove helpful, even though will forecast climate change, scientists check to see how well more potential climate fl ips could be unveiled in the process. On the programs simulate real-world changes from the past. Many the bright side, new discoveries might instead reveal that the models match the basic types of previous climate anomalies likelihood for abrupt change is actually lower than scientists reasonably well—in other words, they reliably reproduce cold suspect or that one change might offset another. —R.B.A.

Perhaps of greater concern than cold the Global Business Network assess the threshold crossings elsewhere. The grain spells up north are the adverse effects possible national security implications of belts that stretch across the interiors of that would probably strike other parts a total shutdown of the North Atlantic many midlatitude continents face a re- of the world concurrently. Records of conveyor. Many scientists, including me, gional risk of prolonged drought. Most climate across broad areas of Africa and think that a moderate slowdown is much climate models produce greater sum- Asia that typically benefi t from a season more likely than a total shutdown; either mertime drying over these areas as aver- of heavy monsoons indicate that these way, the seriousness of the potential out- age global temperatures rise, regardless areas were particularly dry whenever come makes considering the worst-case of what happens in the North Atlantic. the North Atlantic region was colder implications worthwhile. As the Global The same forecasts suggest that green- than the lands around it. Even the cool- Business Network report states, “Ten- house-induced warming will increase ing from a conveyor slowdown might be sions could mount around the world.... rainfall overall, possibly in the form of enough to produce the drying. With bil- Nations with the resources to do so may more severe storms and fl ooding; how- lions of people relying on monsoons to build virtual fortresses around their coun- ever, those events—signifi cant problems water crops, even a minor drought could tries, preserving resources for themselves. on their own—are not expected to offset lead to widespread famine. Less fortunate nations ... may initiate in the droughts. The consequences of future North struggles for access to food, clean water, Summer drying could cause a rela- Atlantic freshening and cooling may or energy.” tively mild drought to worsen and per- make life more diffi cult even for people sist for decades or more. This transition living in regions outside the extreme cold Floods and Droughts would occur because of a vulnerability or drought. Unease over such broad im- even if a slowdown of the North of the grain belts: for precipitation, they pacts spurred the U.S. Department of De- Atlantic conveyor never happens, glob- rely heavily on rainfall that local plants

fense to request that a think tank called al warming could bring about troubling recycle rather than on new moisture COLLINS MATT

68 SCIENTIFIC AMERICAN NOVEMBER 2004 COPYRIGHT 2004 SCIENTIFIC AMERICAN, INC. blown in from elsewhere. The plants’ ers, but damage worsens as the drought surprise is upon us, as suggested by the roots normally absorb water that would lengthens—especially if no one had time U.S. National Research Council. The otherwise soak through the ground to to prepare. Unfortunately, scientists have authors of the council’s report pointed streams and ﬂ ow to the sea. Some of that little ability to predict when abrupt cli- out that some former societies have bent water then returns to the air by evaporat- mate change will occur and what form it in response to climate change when oth- ing through their leaves. As the region will take [see box on opposite page]. ers have broken. The Viking settlers in begins to suffer drier summers, however, Despite the potentially enormous Greenland abandoned their weakening the plants wilt and possibly die, thereby consequences of a sudden climate trans- settlement as the onset of the Little Ice putting less water back into the air. The formation, the vast majority of climate re- Age made their way of life marginal or vital threshold is crossed when the plant search and policymaking has addressed unsustainable, while their neighbors, population shrinks to the point that the gradual shifts—most notably by calling the Thule Inuit, survived. Understanding It appears likely that humans are pushing certain aspects of climate closer to the thresholds that could unleash sudden changes.

recycled rainfall becomes too meager for global reductions of carbon emissions what separates bending from breaking to sustain the population. At that point as a way to slow the gradual rise in global could prove constructive. Plans designed more plants die, and the rainfall dimin- temperatures. Although such reductions to help ease diffi culties if a crisis devel- ishes further—in a vicious cycle like the would probably help limit climate insta- ops could be made at little or no cost. one that turned the Sahara into a desert bility, thought should also be given specif- Communities could plant trees now to 5,000 years ago. The region has shown ically to avoiding abrupt changes. At one help hold soil during the next windy dry no signs of greening ever since. extreme, we might decide to ignore the spell, for example, and they could agree Scientists fear they have not yet iden- prospect altogether and hope that noth- now on who will have access to which tifi ed many of the thresholds that, when ing happens or that we are able to deal water supplies when that resource be- crossed, would lead to changes in re- with whatever does happen; business-as- comes less abundant. gional climates. That knowledge gap is usual did sink the Titanic, but many other For now, it appears likely that humans worrisome, because humans could well unprepared ships have crossed the North are rocking the boat, pushing certain as- be doing many things to tip the climate Atlantic unscathed. On the other hand, pects of climate closer to the thresholds balance in ways we will regret. Dancing we might seriously alter our behavior to that could unleash sudden changes. Such in a canoe is not usually recommended, keep the human effects on climate small events would not trigger a new ice age or yet dance we do: We are replacing for- enough to make a catastrophic shift less otherwise rival the fertile imaginations ests with croplands, which increases how likely. Curbing global warming would of the writers of the silver screen, but much sunlight the land refl ects; we are be a step in the right direction. Further they could pose daunting challenges for pumping water out of the ground, which investigation of climate thresholds and humans and other living things on earth. changes how much water rivers carry to their vulnerabilities to human activities It is well worth considering how societies the oceans; and we are altering the quan- should illuminate other useful actions. might increase their resiliency to the po- tities of trace gases and particulates in the A third strategy would be for societ- tential consequences of an abrupt shift — atmosphere, which modifi es the charac- ies to shore up their abilities to cope with or even how to avoid fl ipping the climate teristics of clouds, rainfall and more. abrupt climate change before the next canoe in the fi rst place. Facing the Future MORE TO EXPLORE negative consequences of a ma- Climate Change 2001: The Scientific Basis. Intergovernmental Panel on Climate Change (IPCC). jor climate shift can be mitigated if the Cambridge University Press, 2001. Available at www.ipcc.ch change occurs gradually or is expected. Abrupt Climate Change: Inevitable Surprises. National Research Council, Committee on Abrupt Farmers anticipating a drought can drill Climate Change. Richard B. Alley, chair. National Academy Press, 2002. wells, or learn to grow crops less depen- Global Climatic Impacts of a Collapse of the Atlantic Thermohaline Circulation. Michael Vellinga and Richard A. Wood in Climatic Change, Vol. 54, No. 3, pages 251–267; August 2002. dent on water, or simply cut their losses Rapid Climate Change. Spencer Weart in The Discovery of Global Warming. Harvard University and move elsewhere. But unexpected Press, 2003. Essay available at www.aip.org/history/climate/pdf/rapid.pdf change can be devastating. A single, sur- An Abrupt Climate Change Scenario and Its Implications for United States National prise drought year may at fi rst bankrupt Security. Peter Schwartz and Doug Randall. October 2003. Available at www.gbn.org/ or starve only the most marginal farm- ArticleDisplayServlet.srv?aid=26231