j.a.pan had a remarkable economic boom when its workforce was predominantly young, but its slowdown over the last two decades has coincided with the aging of its population. In 2012, the j.a.panese bought more adult diapers than baby diapers. By midcentury its median age, the world's oldest, in 2012, at forty-three, will be fifty-six. Globally, the median is projected to increase from twenty-eight today to forty by midcentury.

Whenever there is an unusually large generation of young people compared to the rest of a society, the so-called youth bulge can also contribute to disruptive and even revolutionary pressures if the society does not have an adequate number of job opportunities-particularly for males between the ages of eighteen and twenty-five. Demographic historians believe that the relatively large proportion of young men in France more than 200 years ago contributed to the pressures that resulted in the French Revolution. The same was true during the seventeenth-century English Civil War and the majority of the revolutions in developing countries during the twentieth century. The cultural and political upheavals of the 1960s in the United States coincided with the young adulthood of the postWorld War II baby boom.

In the 1990s, according to Population Action International, nations with more than 40 percent of its adults made up of those aged fifteen to twenty-nine experienced civil conflict at twice the rate of countries generally, and more than two thirds of civil conflicts since the 1970s have been in nations with youth bulges. Among the many factors causing the Arab Spring in 2011 was the disproportionate size of the young adult generation in most of the Arab countries. It is worth remembering, however, that it was a food vendor in Tunisia who set off the Arab Spring during a period of food price hikes around the world.

One of the largest youth bulges in the world today is in Iran, and although the street demonstrations and the Green Revolution have been suppressed brutally, the pressures for societal change appear to be still building. Similarly, Saudi Arabia, where dissent and demonstrations are also suppressed, faces similar demographic pressures for change, because the percentage of its population made up of young men age fifteen to twenty-nine is exceptionally high, and the number of jobs available to them is exceptionally low.

By most of these demographic measures, the United States has a more favorable outlook than many developed countries. Its median age is climbing, but will reach only 40 by midcentury. Its fertility rate is above the replacement rate, partly due to immigration and to the fertility of immigrant populations.

MIGRATIONS.

In 2010, the United Nations reported that the world's migrant population had reached almost 214 million people, driving the percentage of migrants in the population of developed countries to 10 percent, an increase from 7.2 percent twenty years earlier. In the last year for which statistics are available (2009), 740 million internal migrants moved from one region to another inside countries. Cities are the primary destination for these migrants-both international migrants and those who migrate within their own countries from one region to another, almost always from rural areas to cities.

One new trend is that the number of international migrants moving from one developing country to another is now roughly equal to the number of migrants moving from a developing country to developed regions of the world. As the secretary-general of the United Nations put it, "In other words, those moving 'South-to-South' are about as numerous as those moving 'South-to-North.' "

Although migration has, of course, many beneficial effects-not least among them the enrichment of the talent pool in countries and regions to which they relocate-the number of international migrants has also been driving some dangerous trends in many countries. Xenophobia, with its a.s.sociated discrimination and violence against migrants-particularly those with ethnicities, nationalities, cultures, and religions markedly different from the majority in the country they move to-has been most p.r.o.nounced in regions stressed by high unemployment among natives and in countries where the percentage of international migrants has become seen as a threat to the majority's culture, traditions, and future prosperity.

In Athens, neo-n.a.z.i vigilantes have been patrolling the streets and brutally attacking the growing number of Muslim migrants from several countries, including Afghanistan, Pakistan, and Algeria. In Moscow and some other Russian cities, neo-n.a.z.is, skinheads, and other right-wing extremist groups are also brutalizing migrants-many of them from areas like Chechnya in the trans-Caucasus region, where there are significant Muslim populations.

Migrants now make up 20 percent or more of the people in forty-one countries around the world; three quarters of them have less than one million people. There are now thirty-eight larger countries where cross-border migrants make up 10 percent of the population or more.

India will soon complete construction of a 2,100-mile-long, 2.5-meter-high iron fence on its border with Bangladesh. As the nation most affected by the early impacts of climate change, Bangladesh has experienced a surge of internal migration from low-lying coastal areas and offsh.o.r.e islands in the Bay of Bengal, where four million people currently live. The overall population of Bangladesh is expected to increase from 150 million today to 242 million over the next few decades.

Bangladesh has also been the destination for a large number of international migrants from Afghanistan since the U.S. invasion. The presence among these migrants of many jihadists and Taliban members has given rise to concerns by India about an upsurge in Islamic extremism on the Bangladesh side of the border. But the continuing economic stress in Bangladesh is the princ.i.p.al source of pressure for trans-border migration toward India and through India to other destinations.

Even in the United States, where immigration has been a historic success story, the surge of legal and undoc.u.mented migrants in the early part of the twenty-first century created social stress. Twenty percent of all international migrants now live in the United States even though it has only 5 percent of the world's population. During the twelve-month period that ended in July 2011, the number of "non-white" babies born outnumbered Caucasian babies for the first time. The concern over illegal immigration from Mexico and other countries during the same period is cited by domestic terrorism experts as a major factor causing the surge of hate groups.

A RECENT STUDY by the Brookings Inst.i.tution indicates that "minorities accounted for 92 percent of the nation's population growth in the decade that ended in 2010." The number of white children in the U.S. declined by 4.3 million as the number of Hispanic and Asian children increased by 5.5 million. Already, more than half of U.S. cities are minority majority, with the two largest groups represented by Hispanics at 26 percent and African Americans at 22 percent. Hispanics now represent the largest minority group in the United States.

U.S. domestic terrorist groups actually peaked in the 1990s just prior to the bombing of the federal office building in Oklahoma City. The number declined sharply for more than twelve years until the inauguration of Barack Obama, which appeared to trigger a renewed upsurge in 200912 to levels far higher than the previous peak. The Southern Poverty Law Center links the increase to the changes in America's demographic makeup: "This very real and very significant change is represented in the person of Barack Obama. We've of course seen the most remarkable growth in the radical right since 2008, precisely coinciding with Obama's first three years as president."

Ironically, net immigration from Mexico fell to zero in 2012, though immigration from several other countries has continued. Flows of Asian immigrants to the U.S. overtook Hispanics in 2009. And according to the Brookings study, "Even if immigration stopped tomorrow, we will achieve a national minority majority child population by 2050 (by around 2023 if current immigration trends continue)."

The relatively higher birth rate in the Palestinian territories, compared to the Jewish birth rate in Israel, is causing changes in the political a.n.a.lyses by both Palestinians and Israelis of how to evaluate potential options for resolving, or at least managing, the tensions in the region. The same differential birth rate has led to a sevenfold increase in the Arab minority population inside Israel's borders since the modern state was founded, leading to oft-expressed concerns by some Israelis that demographic trends could one day force a choice between the Jewish nature of the state of Israel and the democratic principle of majority rule.

There are also often negative consequences in countries where large numbers of migrants are leaving. Chief among them is the problem caused by a brain drain when highly trained professionals-such as doctors and nurses-leave their countries of origin, in part because their skills make it much easier for them to find lucrative employment and higher standards of living in developed countries. When middle-cla.s.s families migrate, there is often diminished support in their countries of origin for continued investments in public goods like education and health care. At the same time, the increasing percentage of migrant and domestic minority populations in developed countries has sometimes appeared to weaken the social contract supporting the provision of public goods-particularly public education-when phenomena such as white flight to private schools results in less support for public school budgets.

Nevertheless, many destination countries have adopted policies designed to attract higher-skilled migrants. And the need for low-wage workers in many developed countries with smaller than optimal workforces has also led to a significant expansion of temporary worker programs-particularly in the United States, Australia, and the United Kingdom. Colleges and universities have also significantly increased their recruiting of migrant students from foreign countries.

Many of the nations and regions from which migrants originate also experience some positive benefits, particularly in the form of remittances, especially from migrants leaving lower-middle-income countries. The remittances sent by migrants back to their families totaled $351 billion in 2011 and are projected to reach $441 billion in 2014.

The amount of remittances sent back to their communities of origin by internal migrants is believed to be much larger. In China, internal migrants from rural areas send an average of $545 per year back home from the cities where they work. In Bangladesh, the Coalition for the Urban Poor calculates that migrants from rural areas to the capital city of Dhaka routinely send back home as much as 60 percent of their income. Indian migrants from the poor states of Uttar Pradesh, Bihar, and West Bengal routinely send money orders from Mumbai back to their home communities in amounts that make up the majority of money flowing into those three states.

REFUGEES.

Alongside the flows of international and internal migrants are growing numbers of refugees. According to the international treaty on refugees, the definition of a refugee is someone who, unlike a migrant, leaves his or her country of origin due to the fear of violence or persecution. Almost 44 million people around the world have been forced from their nations of origin by conflict or persecution-of which 15.4 million are cla.s.sified as refugees-and another 27.5 million people have been displaced by violence and persecution to new communities within their own country.

The U.N. high commissioner for refugees, Antonio Guterres, notes that 70 percent of current refugees have been in that status for more than five years, and as a result, "it's becoming more and more difficult to find solutions for them." Twelve million among them are stateless, meaning they have no place to go home to. In the last five years, for the first time, more refugees moved to cities than to refugee camps. While equal numbers of migrants traveled to developed and developing countries, 80 percent of refugees live in poor regions of the world.

All of the large source countries for refugees are mired in violent conflicts, including Somalia, the Democratic Republic of the Congo, Myanmar, Colombia, and Sudan. The two largest source countries for refugees are Afghanistan and Iraq. The ill-fated decision by the United States in 2002 to invade Iraq-thus prolonging the conflict in Afghanistan as well, by prematurely removing troops that had encircled Osama bin Laden-has had a cascading impact on the entire region, flooding neighboring countries with refugees.

The three million Afghans displaced by the war in their home country have fled mostly to Pakistan (1.9 million) and Iran (one million). The 1.7 million refugees from Iraq have also gone mostly to neighboring countries. Indeed, according to the World Development Report, more than three quarters of refugees worldwide are hosted in nations neighboring their country of origin. The largest number are now living in Asia and the Pacific (2 million-most of them in South Asia), Sub-Saharan Africa (2.2 million-403,000 of them in one country, Kenya!), and the Middle East and North Africa (another 1.9 million).

However, more than 1.6 million refugees, the vast majority of them Muslim, have found their way to Europe, further exacerbating xenophobic tensions and increasing fears of radicalization of poorly a.s.similated young Muslim populations living in Europe; Muslims already make up 5 percent of Europe's population. The surge of international migrants from North Africa and South Asia into Europe has also triggered a renewal of xenophobia, even in countries previously known for their commitment to tolerance. In several European countries, the combination of economic stress and the growing numbers of immigrants, particularly Muslim immigrants, has disrupted the political balance as extreme right-wing and nativist groups exploit the public's uneasiness.

THE FASTEST GROWING new category of refugees is climate refugees. Although they are not legally cla.s.sified as refugees (because the definition in the Refugee Protocol requires that the source of their motivating fear be violence or persecution from other people), they are nevertheless routinely described as refugees because their migration is not voluntary. In the U.N.'s State of the World's Refugees report from June 2012, U.N. secretary-general Ban Ki-moon noted that the traditional causes of forced displacement, "conflict and human rights abuses," are now "increasingly intertwined with and compounded by other factors," many of them related "to the relentless advance of climate change."

Israel announced a major national plan last May on climate change that included a recommendation to build "sea fences" near its maritime borders on the Red Sea and the Mediterranean, linked with impa.s.sable barriers on its land borders, in order to protect against a predicted wave of climate refugees. "Climate change is already here and requires comprehensive preparations," said Israeli environmental protection minister Gilad Erdan. "The lack of water, warming and sea level rise, even if it will occur on a different schedule, will bring migration movements from all impoverished regions to every place where it is possible to escape this," the study noted.

One of the two leaders of the team authoring the report, Professor Arnon Soffer of the University of Haifa's Geography Department, added, "The migration wave is not a problem for the future. It is today, it is going on now.... It will just increase from day to day." Noting that European navies prevent most boats with migrants from reaching Europe, he said they are forced to go elsewhere, but "in India they shoot, in Nepal they shoot, in j.a.pan they shoot." The team noted that climate refugees are expected from Africa, where approximately 800 lakes have dried up completely in the last decade, including the former largest lake in Africa, Lake Chad, which mobilized many climate refugees eastward into the Darfur region.

Persistent droughts and desertification in Somalia have also contributed to the violent conflict there. Other climate refugees attempting to migrate to Israel are expected from Jordan, the Palestinian territories, Syria, and the Nile Delta in Egypt. In addition, still more internal climate refugees are expected from the Negev, from which many Bedouins have already moved to cities in the center of Israel. Soffer added, "If we want to keep Israel a Jewish state, we will have to defend ourselves from what I call 'climate refugees,' exactly as Europe is doing now."

U.S. a.s.sistant secretary of state Kurt Campbell recently wrote that the impact of climate change on Africa and South Asia, including "the expected decline in food production and fresh drinking water, combined with the increased conflict sparked by resource scarcity," is likely to produce "a surge in the number of Muslim immigrants to the European Union (EU)," doubling Europe's Muslim population within the next twelve years, "and it will be much larger if, as we expect, the effects of climate change spur additional migration from Africa and South Asia."

A few years ago, I visited the southernmost extremity of the European Union, Spain's Canary Islands, just off the coast of West Africa. I found many conversations dominated by concerns of residents about the surge of refugees attempting to migrate by boat from Africa to their most convenient point of entry into the European Union. In some years, more than 20,000 Africans have attempted the dangerous journey across to the Canaries.

Over the next century, the global community can expect millions of climate refugees. Almost 150 million people now live in low-lying areas only one meter or less higher than the current sea level. For each additional meter of sea level rise, roughly 100 million more people will be forced to abandon the places they call home. And this number, of course, does not include refugees from desertifying dryland areas.

The dimensions of the climate crisis are described in Chapter 6, along with the difficult but cost-effective and necessary responses. What is clear now, however, is that even with global warming in its early stages, the growth of human civilization is already pressing hard against limitations that are complicating our ability to provide the essentials of life for billions of people.

ENDANGERED GROUNDWATER AND TOPSOIL.

For example, where topsoil and groundwater are concerned, there is a disconnect between the frenzied rate of exploitation of both these resources on the one hand, and the extremely slow rate with which either resource can be regenerated on the other. Renewable groundwater aquifers fill back up, on average, at the rate of less than one half of one percent per year. Similarly, topsoil regenerates naturally-but at the agonizingly slow rate of approximately 2.5 centimeters every 500 years.

In just the last forty years, the overexploitation of topsoil has led to the loss of a significant amount of productivity on almost one third of the arable land on Earth. Without urgent action, the majority of the Earth's topsoil could be severely degraded or lost before the end of this century. In China, topsoil is being lost fifty-seven times faster than this natural replacement process; in Europe seventeen times faster. According to the National Academy of Sciences, it is being lost in the United States ten times faster than it can be replenished. Ethiopia is now losing almost two billion tons of topsoil every year to rain washing the erodible soils down the steep slopes of its terrain.

In the case of groundwater, the nearly total depletion of some important aquifers and the sharply dropping levels of others have now focused the attention of experts in many countries on the future of this resource. The doubling of the global withdrawal rate over the last half century-and the projection that withdrawals will continue to increase at an even faster pace-have many experts beginning to get very worried. In many areas, the withdrawals from aquifers now far exceed the rate of replenishment; many aquifers are now falling several meters per year.

IT IS AS if we are willfully blind to the basic underlying reality of our relationship to the Earth's limited resources. But this seeming blindness is reinforced by the world's princ.i.p.al method of accounting for natural resources, which treats their use as income rather than withdrawals from capital. This is, in the words of economist Herman Daly, "a colossal accounting error.... At least we should put the costs and the benefits in separate accounts for comparison."

The basic distinction between operating income and withdrawals from capital is crucial, whether one is accounting for a company or a nation. In the words of a cla.s.sic accounting text, if this distinction is misunderstood and improperly made, it leads to "practical confusion between income and capital." Another seminal accounting text notes that "net income of an ent.i.ty for any period is the maximum amount that can be distributed to its owners during the period and still allow the ent.i.ty to have the same net worth at the end of the period as at the beginning.... In other words, capital must be maintained before an ent.i.ty can earn income." This same principle holds true for nations and for the world as a whole. In recognition of this principle, the U.N. Statistical Commission in 2012 adopted a "system of environmental-economic accounts" as a step toward integrating environmental externalities. In 2007, the European Union launched its "beyond GDP" initiative, and is due to release an a.s.sessment by all member states of their "natural capital" in 2014.

When Simon Kuznets warned in 1937 that misuse of GDP would make us vulnerable to such accounting errors and could lead to a form of willful blindness, he noted that conflicts over resources might well exacerbate the risk inherent in the admittedly flawed design of his elaborate accounting system: The valuable capacity of the human mind to simplify a complex situation in a compact characterization becomes dangerous when not controlled in terms of definitely stated criteria. With quant.i.tative measurements especially, the definiteness of the result suggests, often misleadingly, a precision and simplicity in the outlines of the object measured. Measurements of national income are subject to this type of illusion ... especially since they deal with matters that are the center of conflict of opposing social groups where the effectiveness of an argument is often contingent on oversimplification.

In an example of the precise problem Kuznets was antic.i.p.ating, today-all around the world-calculations about the impact of groundwater withdrawals are often at "the center of conflict of opposing social groups." Often, officials in regions where water supplies are shared with other regions or countries-and whose farms and businesses would be disrupted by any change in water allocations-have strong incentives to minimize the seriousness of the problem-putting off for the future a problem they would rather not deal with in the near term. It's an all too familiar challenge for anyone who works on global warming.

In just one of many examples of this particular variety of denial, when an expert from the University of Oklahoma, Luo Yiqi, visited Inner Mongolia in northern China a few years ago to study desertification, he was astonished to see fields of rice (one of the most water-intensive crops) grown with water that authorities allowed to be pumped at grossly unsustainable rates from deep aquifers. "Apparently," he noted dryly, "farmers did not get enough scientific guidance."

The regrettable decision to ignore the depreciation of natural resources, while accounting precisely for the depreciation of capital goods, may have been subtly influenced by the state of the world when this formula was created in the 1930s. We were still in the last stages of the colonial era, when limitations on supplies of natural resources seemed irrelevant; industrialized countries could simply obtain more in their colonial possessions, where the supply seemed, for all intents and purposes, limitless. Global population has tripled since the national accounts were adopted, and the dangerous illusion that Kuznets warned about is now at the heart of the world's failure to recognize the twin dangers of unsustainable depletion of both topsoil and groundwater.

Since the beginning of the Agricultural Revolution, these two strategic resources have both been essential for the production of food. The irrigation of crops emerged roughly 7,000 years ago and the Green Revolution of the twentieth century increased agriculture's dependence on irrigation-particularly in China, where 80 percent of the harvest depends on irrigation, and India, where 60 percent depends on irrigation. (The U.S. depends far less on irrigation.) Large dams for water storage gained popularity in the late nineteenth and early twentieth centuries. There are now 45,000 large dams in the world, including on all twenty-one of the world's longest rivers. FDR's economic stimulus program in the 1930s resulted in large-scale dam construction by the Tennessee Valley Authority in my home region, and the Bonneville Power Administration in the Pacific Northwest-and of course, the majestic Hoover Dam on the Colorado River, which was the tallest in the U.S. when it was built seventy years ago.

Prior to the Industrial Revolution and the explosion of urban populations, more than 90 percent of global freshwater was used for agriculture. In more recent decades, the compet.i.tion for water between agriculture, manufacturing, and fast-growing thirsty cities has led to growing disputes over water allocation-disputes that agriculture often loses. Today, more than 70 percent of the world's freshwater is used to grow food, even though 780 million people in the world still lack access to safe drinking water. As noted earlier, the world has made significant progress in reducing the number of people who lack access to improved water resources (though little progress has been made in preventing the contamination of freshwater sources-both surface and groundwater resources-from human and animal waste and other pollutants).

Some deep aquifers have long been sealed from surface water. A recently tapped aquifer in the Northeastern United States, Patapsco (under the state of Maryland) has water found to be one million years old. Similarly, the Nubian Aquifer (underneath the Sahara), the Great Artesian Basin (underneath northeastern Australia), and the Alberta Basin (underneath western Canada) all also have water more than one million years old. But although these "fossil" aquifers are nonreplenishable, most scientists believe they are limited in their supply of water; the vast majority of aquifers are replenished slowly as rainwater filters down to them.

Until recently, the amount of information about groundwater depletion rates was spotty at best, and according to one expert, the threat to the resource is a cla.s.sic case of "out of sight, out of mind." Indeed, so much water is now being withdrawn from underground aquifers that it is believed by experts to account for 20 percent of the sea level rise in recent decades (although scientists forecast that the accelerating ice loss from Greenland and Antarctica will dramatically increase sea level rise later in this century).

The highest rates of groundwater depletion are in northwest India and northeast Pakistan, the Central Valley of California, and northeastern China. One Chinese groundwater specialist found that an aquifer in northern China with water 30,000 years old was being used unsustainably to irrigate crops in dryland areas. China has embarked upon the largest water project in history-the SouthNorth Water Transfer Project that has been under construction for decades, intended to remedy water shortages in northern China. Asia, which has 29 percent of the world's freshwater resources, is now using more than 50 percent of the world's water. According to the United Nations, "In 2000, about 57% of the world's freshwater withdrawal, and 70% of its consumption, took place in Asia, where the world's major irrigated lands are located."

Africa has only 9 percent of the world's freshwater, but is using 13 percent, and is expected by U.N. experts to have the most intensive increases in water withdrawal in the coming decades. Europe is consuming only a slightly larger percentage than its own supply. The Americas are fortunate in having more water than they use, but large regions-particularly Mexico and the Southwestern U.S.-are already experiencing severe shortages. In 2011, more than one million head of cattle were herded north from Texas to wetter, cooler pastures. Few expect them ever to return.

According to a study by the Scripps Inst.i.tute, there is a "50-50 chance" that Lake Mead-the largest man-made lake in the western hemisphere, the one formed by Hoover Dam-will run completely dry before the end of this decade. In addition, according to the U.S. Department of Agriculture, the water table beneath three of the largest grain-producing states-Kansas, Texas, and Oklahoma-has dropped more than 100 feet, forcing many farmers to abandon irrigation. Reservoirs in the state of Georgia have also been running at dangerously low levels for several years.

Improving the efficiency of water use is a cost-effective option for ameliorating shortages in some areas. Many aging water distribution systems leak extraordinary amounts of water. In the U.S., for example, an important urban water line bursts every two minutes on average, twenty-four hours a day. Some portions of older urban water systems were built over 160 years ago, and since then, have been-like groundwater resources-"out of sight, out of mind." Repairing munic.i.p.al water pipes is expensive, but some cities are belatedly recognizing the necessity of undertaking this task.

According to ecologist Peter Gleick, we should view efficiency as a giant wellspring that could provide vast new quant.i.ties of needed freshwater. Unfortunately, this wellspring, like many of the aquifers now being recklessly depleted, also seems to be out of sight, out of mind. The majority of agricultural irrigation practices are still extremely wasteful. Switching to scientifically precise drip irrigation techniques is cost-effective in most agricultural operations, but many farmers have been slow to make the change. Another benefit of switching to more efficient and precise methods of irrigation is that wasteful and excessive irrigation of crops increases the salinity of soils-because the irrigation water usually contains small amounts of salt that build up with continued use.

The recycling of water is growing in popularity. Some communities already require the use of greywater-used water that is not suitable for drinking but is safe for watering plants. The more controversial recycling proposals take sewage water and remove all of the contaminants, purify it, and put it into drinking water systems. There is still a great deal of consumer resistance to these plans, but some communities have successfully implemented the approach.

In regions where rainfall is becoming more concentrated in large downpours-interrupted by longer periods of drought-many experts are calling for the increased use of cisterns to capture more of the rainfall and store it for drinking water. This once common practice fell out of favor with the extension of underground water lines from reservoirs. I remember the cisterns we used to have on our family farm when I was a boy. We stopped using them when we got "city water."

THE STATE OF the world's topsoil is threatened by the same willfully blind overexploitation that has caused shortages of freshwater. In the world's prevailing system of accounting, neither water nor topsoil are a.s.signed any value. Therefore, wasteful and destructive practices that diminish the supplies of both are invisible in the world's economic calculations. Yet topsoil, along with water, is the basis for virtually all human life on Earth. More than 99.7 percent of food consumed by human beings comes from cropland, more specifically from the six to eight inches of topsoil that cover roughly 10 percent of the Earth's surface.

On a global basis, we are effectively strip-mining this crucial resource in an unsustainable pattern, by recklessly plowing erodible soils, overgrazing gra.s.slands, taking arable land for buildings and roads to accommodate urban and suburban sprawl, tolerating reckless deforestation, and failing to use proven land management techniques that replenish soil carbon and nitrogen.

At present, every kilogram of corn produced in the American Midwest results in the loss of more than a kilogram of topsoil. In some states, such as Iowa, the ratio is even higher: 1.5 kilograms of topsoil lost for each kilogram of grain. These rates of soil loss are not sustainable. They deplete soil carbon, thus damaging the productivity of the soil over time, and accelerate the emission of carbon dioxide into the atmosphere.

We already know how to slow and reverse soil erosion, but global leadership would be required to mobilize the community of nations in the same way that FDR mobilized the United States in the 1930s. Organic agriculture with low-till and no-till practices can sharply reduce soil loss while simultaneously increasing the fertility of the topsoil. Crop rotation, a technique that used to be widespread before industrial agriculture took over, can replenish soil carbon and nitrogen.

Another once common technique that has since been abandoned in large areas of the world is the recycling of animal manure as fertilizer for crops. Factory farming-the cl.u.s.tering of thousands of head of livestock in crowded feedlots and feeding them corn-has turned this natural fertilizer into highly acidic toxic waste that is harmful to crops and thus becomes an expensive liability instead of a valued a.s.set.

A major study in 2012 by leading researchers at the University of Minnesota, Iowa State University, and the Agricultural Research Service of the U.S. Department of Agriculture showed that the use of nontoxic manure as fertilizer and a three-year crop rotation designed to replenish soil fertility reduced the need for herbicides and nitrogen fertilizer by almost 90 percent, without reducing profits. One of the researchers, Professor Matt Liebman of Iowa State, said that one of the reasons farmers do not use the approach recommended in the study is that "there's no cost a.s.signed to environmental externalities."

For the last century, modern agriculture has been based on heavy use of synthetic nitrogen fertilizer-90 percent of the cost of which is from natural gas, from which virtually all of the nitrogen is derived. However, agricultural productivity growth has been slowing even as fertilizer use per acre has been increasing dramatically. Moreover, the heavy use of nitrogen in agriculture has caused significant water pollution problems around the world as it runs off farmland with the rain and feeds uncontrolled ma.s.sive algae blooms in coastal regions of the ocean-and dead zones, areas devoid of life, which are growing in several ocean regions, including the part of the Gulf of Mexico into which the Mississippi River drains. In China the use of synthetic nitrogen fertilizer has increased by 40 percent in the last two decades even though grain production has remained relatively stable; it is this nitrogen runoff that has produced the recent spectacular algae blooms in Chinese rivers, lakes, and coastal areas.

Additional nitrogen emissions from the combustion of fossil fuels in factories, on farms, and in cars and trucks have created significant air pollution problems, particularly in the U.S., China, Southeast Asia, and parts of Latin America. More efficient and targeted use of nitrogen fertilizers, and tighter restrictions on emissions from factories and vehicles, are needed to address the problem.

While nitrogen supplies are not limited, there is a potentially serious emerging limit to the supply of another crucial component of fertilizer-phosphorus, which is a relatively rare element on the Earth. Even as conventional sources of phosphorus are running out, modern agricultural techniques have tripled the depletion of phosphorus from cropland.

A PHOSPHORUS CARTEL?.

The first warning about a phosphorus shortage in a 1938 message to Congress, by President Roosevelt, led to a successful worldwide search for additional reserves-including the discovery of phosphates near Tampa, Florida, where 65 percent of U.S. production now takes place. But while the United States produces 40 percent of the world's corn and soybeans, it produces only 19 percent of the world's phosphorus, which, in the long run, is essential for agriculture to continue-and so now the search for new reserves is beginning again.

Forty percent of the world's current supply of phosphates (the most common form in which phosphorus occurs) is in Morocco, which has been called the "Saudi Arabia of phosphorus." The next largest reserves are found in China, which imposed a 135 percent tariff on exports during the 2008 food price crisis. Many experts fear that similar h.o.a.rding of phosphorus could occur if food prices continue to go up, although other experts are more sanguine about the possibility of finding new sources in unconventional locations, such as the ocean floor.

Phosphorus is essential to all life, including human life. It makes up the backbone of DNA, among other things, and fully one percent of the bodyweight of human beings is made up of phosphorus; in fact, the seven billion people on Earth discard large quant.i.ties in urine every day. Some countries are now actively exploring the recycling of urine in order to extend the supplies of phosphorus for fertilizers.

The addition of rhizobium bacteria and mycorrhizal fungi to soils as seeds are planted can improve crop yields and also speed the recovery of soil fertility and enhance the sequestration of soil carbon. The planting of leguminous trees every thirty feet or so as buffer strips and contour hedges can replenish nitrogen in the soil and further protect against erosion. Leaving the majority of crop residue-like corn stover-on the land during and after harvesting the crop can also restore the fertility of the soil while diminishing erosion. The use of biochar (from sustainable sources) in a carefully managed way can also improve yields and soil quality. The reduction of meat as a percentage of a healthy diet can relieve pressure on the Earth's topsoil. And the expansion of small-scale organic gardens in countries with a surplus of arable land could potentially add significant volumes of fresh food to the world supply, as they did in Western countries when Victory Gardens were planted during World War II.

But perhaps the single most effective measure to protect topsoil would be to use carbon credits to provide an additional source of income for farmers who pay careful attention to safeguarding and improving the carbon content and fertility of their soils.

So long as the world ignores the value of topsoil in its constant calculations of growth and productivity, the demands placed on agriculture by the combination of growing population and growing per capita consumption of food will continue putting the future of topsoil at severe risk. At current consumption rates (which are still increasing), we need an additional 15 million hectares each year to keep up with the extra food production needed for the increasing population. Yet we are destroying and losing approximately 10 million hectares (approximately 25 million acres) every year. At present, much of the additional cropland being developed results in deforestation-often in forest areas that have very thin topsoils that are quickly depleted by wind and water after the trees are gone. In addition, the more forestland that is converted to farmland, the more biodiversity is lost.

In some respects, the global topsoil crisis is an echo of what happened in the United States in the first third of the twentieth century when the first ma.s.s market tractors-pulling the more efficient plows that had been invented three quarters of a century earlier-broke the sod of erodible gra.s.slands in the Midwest for crops; over the next three decades the vulnerable topsoil was washed and blown away, creating the Dust Bowl of the 1930s. Less well known in the U.S. is the even larger tragedy experienced in Central Asia during the 1950s when the USSR plowed an enormous area of gra.s.sland-mostly in Kazakhstan (1954)-and created their own Dust Bowl.

Another epic land-use catastrophe occurred in Central Asia in the 1960s, when the USSR embarked on a shortsighted plan to grow thirsty cotton crops in dryland areas of Uzbekistan and Turkmenistan. So much water was diverted from two rivers-the Amu Darya and the Syr Darya-that the world's fourth largest inland sea, the Aral Sea, almost completely disappeared. I visited the Aral Sea two decades ago and saw firsthand the tragedy that resulted for the people who used to depend on it.

DUST STORMS AHEAD.

My father's generation was motivated by the U.S. soil erosion crisis to adopt new land management techniques. One of the great accomplishments of FDR's New Deal was the ma.s.sive program to reconvert eroded land to gra.s.sland and a nationwide effort to fight soil erosion. I still remember my father teaching me when I was a young boy how to stop gullies before they began cutting deep into the soil, and how to recognize the richest soil-it's black from all the organic carbon in the soil.

Modern-day dust storms are now once again increasing in size and frequency as drylands are being overgrazed and erodible soils are subjected to higher temperatures and stronger winds. "Drylands are on the front line of the climate change challenges for the world," said Luc Gnacadja, who heads the U.N. Convention to Combat Desertification. The U.N. Environment Programme reports that land degradation in drylands threatens the way of life for an estimated one billion people in 100 countries. Desertification is taking a toll on topsoil and destroying arable cropland-particularly in regions of Africa north and south of the Sahara, throughout the Middle East, in Central Asia, and in large areas of China, where overgrazing, poor cultivation techniques, and urban sprawl are contributing significantly to the phenomenon.

In the U.S., in July of 2011, Phoenix, Arizona, was covered with dust when, in the words of the National Weather Service, "A very large and historic dust storm moved through a large swatch of Arizona." Although these Southwestern U.S. dust storms, often called hab.o.o.bs, are not new, Phoenix has had an unusually large number of them in recent years-seven in 2011 alone.

The U.S. Geological Survey and UCLA conducted a study in 2011 that predicted "accelerated rates of dust emission from wind erosion" as a result of climate change in the Southwestern United States. Climate expert Joseph Romm has recommended use of the term "dust-bowlification" as a way of describing what is in store for many regions of desertifying drylands.

Lester Brown, long one of the world's leading environmental experts, points out that the two most significant desertifying areas now generating dust storms are in north-central China and in the areas of Central Africa that lie on the southern edge of the Sahara Desert. As Brown puts it, "Two huge dust bowls are forming, one across northwest China, western Mongolia, and central Asia; the other in central Africa."

According to geographer Andrew Goudie at Oxford, dust storms from the Sahara have increased tenfold during the last fifty years. The chairman of the African Union, Jean Ping, says, "The phenomenon of desertification affects 43 percent of productive lands, or 70 percent of economic activity and 40 percent of the continent's population." In large areas of Sub-Saharan Africa, soil carbon content is now lower than it was in the United States' Midwest just prior to the Dust Bowl.

In Nigeria, while human population increased fourfold over the last sixty years, the number of livestock exploded from six million to more than 100 million. Partly as a result, the northern region of Nigeria is being desertified-which is contributing to growing clashes between Muslims moving from the north into non-Muslim areas in southern Nigeria. Growth in the population of both humans and livestock is also driving compet.i.tion for land in other drying areas of Africa and has led to deadly conflicts between herders and farmers (whose ethnicities and religions are also different), who have fought one another in Sudan, Mali, and elsewhere.

The same livestock population explosion is damaging the overgrazed gra.s.slands surrounding China's Gobi Desert, where the dust storms are also increasing dramatically. While the United States and China have roughly the same amount of grazing land and roughly the same number of cattle (80100 million), China has 284 million sheep and goats compared to less than 10 million in the United States. According to the latest statistics available, China is now losing almost 1,400 square miles of arable land to deserts every year.

The U.S. emba.s.sy in China has used satellite photos to ill.u.s.trate the "desert mergers and acquisitions" in north-central China where two deserts in Inner Mongolia and Gansu Province are merging and expanding. In Xinjiang Province in northwestern China, the same thing is happening, as the Taklamakan and k.u.mtag deserts are also merging and expanding. More than 24,000 villages and their surrounding cropland have had to be at least partially abandoned in these northern and western regions of China. Similar tragedies are unfolding in both Iran and Afghanistan, both of which have already abandoned many villages to the encroaching desert.

While the ma.s.sive sandstorms in China and Africa are capturing attention today, Lester Brown warns, "A third ma.s.sive cropland expansion is now taking place in the Brazilian Amazon Basin and in the cerrado, a savannah-like region bordering the basin on its south side." These soils are highly erodible and the results are predictable: low yields, followed by soil erosion on a ma.s.sive scale. The knock-on effects also include the further expansion of cattle ranching into the Amazon rainforest, adding even more risk to the integrity of that globally important ecosystem. The Amazon has already suffered from two "hundred-year droughts" in the last seven years. As the deforestation and the wildfires continue in the Amazon, many experts have expressed concern that the Amazon is in danger of being transformed over time from the greatest tropical rainforest on Earth into a ma.s.sive dryland region.

With the rapidly increasing populations in Africa and the Middle East, and impending food shortages, it is remarkable that the world has paid so little attention to the desertification crisis. According to the U.N. Convention to Combat Desertification's Luc Gnacadja, the reason desertification has not become a higher priority is that 90 percent of the people affected live in developing countries. It is another example of the imbalance of power in the world-and the lack of leadership. Gnacadja added, "The top 20 centimeters of soil is all that stands between us and extinction."

The loss of arable land is particularly acute in the most populated nation of North Africa. According to the United Nations, Egypt is now losing an incredible 3.5 acres per hour of its fertile agricultural land in the Nile Delta-mainly because of new construction and urban sprawl to accommodate additional shelter for Egypt's fast growing population.

In addition, rising sea level in the Mediterranean is already pushing salt.w.a.ter aquifers upward in areas near the coast, resulting in the loss of cropland to salinization. Salinization is also occurring in the rich Ganges Delta, the Mekong Delta, and in other so-called mega-deltas. A one-meter rise in sea level-less than that predicted during this century-would inundate a significant percentage of the most fertile soils in the Nile Delta-from whence 40 percent of Egypt's food production comes.

The pressure created by the increased use of water-intensive agriculture, population growth, and economic expansion is increasing tensions over the allocation of river water in several regions of the world where the management of rivers and dams affects watersheds shared by multiple countries. The potential for conflict is building in the Nile River watershed, where the largest country dependent on the Nile, Egypt, now benefits from its allocation of the majority of the Nile's water. But Ethiopia, where 85 percent of the Nile's headwaters originate but where very little of that water is now consumed, will double its population in the next thirty-seven years-and Sudan, which also depends on the Nile, is expected to increase its population 85 percent during the same period.

To the east of Egypt, the decision by Turkey to take a larger portion of the headwaters from the Tigris and Euphrates has led to growing complaints by Iraq and Syria that they are being treated unjustly. Both Iraq and Syria have been overdepleting their underground aquifers as they seek a resolution of the issue. Similarly, China's effort to take for itself a larger percentage of water from rivers that flow into Southeast Asia and India is raising tensions that will only get worse as populations in all the affected countries increase. In the United States, the growing conflicts over allocations of water in the West from the Colorado River system are being waged in court. But the underlying cause in all four of these giant watersheds is the same: there's more demand for water and less supply.

Conflicts between nations over access to freshwater have historically produced very few wars, though conflicts within nations over water have frequently produced social tensions and occasional violent clashes. By contrast, conflicts over land have, of course, frequently caused wars in the past.

A NEW SCRAMBLE IN AFRICA.

In our new globalized economy, some nations with growing populations and shrinking resources of topsoil and water for agriculture are embarking on large-scale projects to purchase vast tracts of arable land in other countries-particularly in Africa, where an estimated one third of the world's uncultivated arable land is found. The degree of control that African governments-and the elites that run many of them-have over property rights is much greater in many parts of Africa where tribal property rights predating the colonial era are too easily ignored.

China, India, the Republic of Korea, Saudi Arabia, and other countries, along with multinational corporations and even hedge funds investing money from U.S. universities, are buying up large amounts of land in Africa to produce wheat and other crops for their own consumption and for sale in global markets. "It's a new colonialism, it's like the scramble of Africa in [the] 19th century whereby our resources were exploited to develop the Western world," said Makambo Lotorobo, an official with a Kenyan NGO, Friends of Lake Turkana.

"There is no doubt that this is not just about land, this is about water," said Philip Woodhouse from the University of Manchester. Devlin Kuyek, a researcher with GRAIN, an NGO specializing in food and agriculture issues, added, "Rich countries are eyeing Africa not just for a healthy return on capital, but also as an insurance policy."

This has led to an agricultural real estate boom in Africa. More than one third of Liberia's land, for example, has been sold to private investors. According to an a.n.a.lysis by the Rights and Resources Initiative, a Washington-based international coalition of NGOs, the Democratic Republic of the Congo has signed deals with foreign owners for 48.8 percent of its agricultural land; Mozambique has signed deals with foreign growers for 21.1 percent of its land. Almost 10 percent of the land in South Sudan (according to Norwegian a.n.a.lysts)-and 25 percent of the best acreage around its capital-was sold to investors after the country won its independence in 2011. China reached an agreement with the Democratic Republic of the Congo to grow palm oil for biofuel on 2.8 million hectares of land. There is disagreement among experts on how much of the land involved in these ma.s.sive African purchases is being used for biofuels. The World Bank calculated that in 2009, 21 percent were for biofuels; the International Land Coalition calculated that 44 percent was dedicated to biofuels.

The South Korean multinational corporation Daewoo attempted to purchase almost half of the arable land in Madagascar, though public riots led to a cancellation of the contract (South Korean companies purchased 700,000 hectares in northern Sudan for wheat, according to a study by The Guardian, and the United Arab Emirates purchased slightly more-750,000 hectares).

In Ethiopia, where 8.2 percent of agricultural land has been signed over to foreigners, Nyikaw Ochalla, originally from the Gambella region and who is now living in the United Kingdom, told The Guardian, "The foreign companies are arriving in large numbers, depriving people of land they have used for centuries. There is no consultation with the indigenous population. The deals are done secretly. The only thing the local people see is people coming with lots of tractors to invade their lands. All the land round my family village of Illia has been taken over and is being cleared. People now have to work for an Indian company. Their land has been compulsorily taken and they have been given no compensation. People cannot believe what is happening. Thousands of people will be affected and people will go hungry."

The World Bank a.n.a.lyzed reports of international agricultural property deals between 2008 and 2009 and concluded that during that two-year period, foreign nations and corporations purchased almost 80 million hectares of land-approximately the area of the nation of Pakistan-and that two thirds of the deals were in Africa. In addition to the sheer scale of the international land purchases and long-term leases in Africa, other concerns highlighted by African and international NGOs include problems with the use of water, soil management, and the impact on local farmers whose precolonial tenure rights are often unenforceable. In Uganda, where 14.6 percent of agricultural lands have been signed over to foreign growers, 20,000 people have claimed they were unjustly evicted from their own land; the case is pending in Ugandan courts.