European settlement of North America has involved monumental environmental change. From the late 19th century to the present, agricultural practices in the Great Plains of the United States have dramatically reduced soil organic carbon (C) levels and increased greenhouse gas (GHG) fluxes in this region. This paper details the development of an innovative method to assess these processes. Detailed land-use data sets that specify complete agricultural histories for 21 representative Great Plains counties reflect historical changes in agricultural practices and drive the biogeochemical model, DAYCENT, to simulate 120 years of cropping and related ecosystem consequences. Model outputs include yields of all major crops, soil and system C levels, soil trace-gas fluxes (N2O emissions and CH4 consumption), and soil nitrogen mineralization rates. Comparisons between simulated and observed yields allowed us to adjust and refine model inputs, and then to verify and validate the results. These verification and validation exercises produced measures of model fit that indicated the appropriateness of this approach for estimating historical changes in crop yield. Initial cultivation of native grass and continued farming produced a significant loss of soil C over decades, and declining soil fertility led to reduced crop yields. This process was accompanied by a large GHG release, which subsided as soil fertility decreased. Later, irrigation, nitrogen-fertilizer application, and reduced cultivation intensity restored soil fertility and increased crop yields, but led to increased N2O emissions that reversed the decline in net GHG release. By drawing on both historical evidence of land-use change and scientific models that estimate the environmental consequences of those changes, this paper offers an improved way to understand the short- and long-term ecosystem effects of 120 years of cropping in the Great Plains.

The Great Plains region of the United States is an agricultural production center for the global market and, as such, an important source of greenhouse gas (GHG) emissions. This article uses historical agricultural census data and ecosystem models to estimate the magnitude of annual GHG fluxes from all agricultural sources (e.g., cropping, livestock raising, irrigation, fertilizer production, tractor use) in the Great Plains from 1870 to 2000. Here, we show that carbon (C) released during the plow-out of native grasslands was the largest source of GHG emissions before 1930, whereas livestock production, direct energy use, and soil nitrous oxide emissions are currently the largest sources. Climatic factors mediate these emissions, with cool and wet weather promoting C sequestration and hot and dry weather increasing GHG release. This analysis demonstrates the long-term ecosystem consequences of both historical and current agricultural activities, but also indicates that adoption of available alternative management practices could substantially mitigate agricultural GHG fluxes, ranging from a 34% reduction with a 25% adoption rate to as much as complete elimination with possible net sequestration of C when a greater proportion of farmers adopt new agricultural practices.

Recent scholarship on Mexican Americans in the United States, relying largely on qualitative evidence, sees racism and exploitation as the major explanatory factors in their history. Using representative samples of persons of Mexican origin, we argue that immigration is fundamental to their historical experience. A small, beleaguered community in 1850, the Mexican-origin population grew during the late nineteenth century due to greater security under US jurisdiction. However, immigration between 1900 and 1930 created a Southwest broadly identified with persons of Mexican origin. Economic development in Mexico, restriction of European immigration to the United States, and extreme cross-border wage differentials prompted extensive emigration. Despite low human capital, circular migration, and discrimination, immigrant Mexicans earned substantially higher wages than workers in Mexico or native-born Hispanics in the United States. They followed typical immigrant paths toward urban areas with high wages. Prior to 1930, their marked tendency to repatriate was not “constructed” or compelled by the state or employers, but fit a conventional immigrant strategy. During the Depression, many persons of Mexican origin migrated to Mexico; some were deported or coerced, but others followed this well-established repatriation strategy. The remaining Mexican-origin population, increasingly native born, enjoyed extraordinary socioeconomic gains in the 1940s; upward mobility, their family forms, and rising political activity resembled those of previous immigrant-origin communities. In the same decade, however, the Bracero Program prompted mass illegal immigration and mass deportation, a pattern replicated throughout the late twentieth century. These conditions repeatedly replenished ethnicity and reignited nativism, presenting a challenge not faced by any other immigrant group in US history.

Scholars conventionally assert that government authorities forcibly expelled 500,000 persons of Mexican origin from the U.S. in the 1930s, with more than half of those removed U.S. citizens. Estimates using census data indicate substantially lower numbers, limited governmental involvement, fewer citizens, and considerable voluntary departure. Voluntary decisions fit the repatriation strategy that had been common among young Mexican immigrants in the 1920s. Ironically, the 1940s Bracero Program, designed by Mexico and the U.S. to replicate the 1920s pattern of circular migration, led instead to massive illegal immigration and unprecedented levels of deportation.

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Big data is an exciting prospect for the field of economic history, which has long depended on the acquisition, keying, and cleaning of scarce numerical information about the past. This article examines two areas in which economic historians are already using big data - population and environment - discussing ways in which increased frequency of observation, denser samples, and smaller geographic units allow us to analyze the past with greater precision and often to track individuals, places, and phenomena across time. We also explore promising new sources of big data: organically created economic data, high resolution images, and textual corpora.

Chapter 6 documents the fragmentation of what had previously been a consensus regarding global population growth at the end of the 1960s and beginning of the 1970s, resulting in the emergence of two separate factions. The population establishment continued to promote the position of the erstwhile consensus, which held that rapid population growth in developing countries was a barrier to economic development and could be adequately slowed through voluntary family planning programs. The population bombers contended that population growth anywhere in the world posed an immediate existential threat to the natural environment and American national security and needed to be halted through population control measures that demographers had previously rejected as coercive. These two positions went head-to-head at the UN World Population Conference in 1974, where both were rejected by leaders of developing countries.

Building the Population Bomb examines how human population came to be understood as a problem in the twentieth century, how it became an object of intervention for governments, scientists, and nongovernmental organizations, and how some forms of intervention got coded as legitimate while others were recognized as coercive. It traces the emergence and growth of two scientific perspectives on population from the 1920s to the present. The first, rooted in the natural sciences, considered the world’s population as a whole in relation to natural resources. The second, rooted in the social sciences, considered national population growth rates in relation to economic growth. These two perspectives converged briefly after World War II, convincing world leaders that population growth posed a barrier to economic development and a threat to worldwide peace and environmental integrity. The book documents how this overpopulation consensus attracted vast sums of money to demography and population control, and teases out the differences between population control, birth control, and family planning. It concludes with the fracturing of this consensus at the end of the 1960s, constituting the factions that structure today’s debates over whether the world’s population is growing too quickly or not quickly enough, and over what should be done about it. The book documents how population growth came to take the blame for the world’s most complex and pressing problems, and how efforts to solve “the population problem” have diverted attention and resources from the pursuit of economic, environmental, and reproductive justice.