Chad Monfreda

Solutions for a cultivated planet

Increasing population and consumption are placing unprecedented demands on agriculture and natural resources. Today, approximately a billion people are chronically malnourished while our agricultural systems are concurrently degrading land, water, biodiversity and climate on a global scale. To meet the world’s future food security and sustainability needs, food production must grow substantially while, at the same time, agriculture’s environmental footprint must shrink dramatically. Here we analyse solutions to this dilemma, showing that tremendous progress could be made by halting agricultural expansion, closing ‘yield gaps’ on underperforming lands, increasing cropping efficiency, shifting diets and reducing waste. Together, these strategies could double food production while greatly reducing the environmental impacts of agriculture.

Farming the planet: 1. Geographic distribution of global agricultural lands in the year 2000

million km 2 of cropland (12% of the Earth’s ice-free land surface) and 28.0 (90% confidence range of 23.6–30.0) million km 2 of pasture (22%) in the year 2000.

Tracking the ecological overshoot of the human economy

Sustainability requires living within the regenerative capacity of the biosphere. In an attempt to measure the extent to which humanity satisfies this requirement, we use existing data to translate human demand on the environment into the area required for the production of food and other goods, together with the absorption of wastes. Our accounts indicate that human demand may well have exceeded the biospheres regenerative capacity since the 1980s. According to this preliminary and exploratory assessment, humanitys load corresponded to 70% of the capacity of the global biosphere in 1961, and grew to 120% in 1999.

Carbon payback times for crop-based biofuel expansion in the tropics: the effects of changing yield and technology

Biofuels from land-rich tropical countries may help displace foreign petroleum imports for many industrialized nations, providing a possible solution to the twin challenges of energy security and climate change. But concern is mounting that crop-based biofuels will increase net greenhouse gas emissions if feedstocks are produced by expanding agricultural lands. Here we quantify the ‘carbon payback time’ for a range of biofuel crop expansion pathways in the tropics. We use a new, geographically detailed database of crop locations and yields, along with updated vegetation and soil biomass estimates, to provide carbon payback estimates that are more regionally specific than those in previous studies. Using this cropland database, we also estimate carbon payback times under different scenarios of future crop yields, biofuel technologies, and petroleum sources. Under current conditions, the expansion of biofuels into productive tropical ecosystems will always lead to net carbon emissions for decades to centuries, while expanding into degraded or already cultivated land will provide almost immediate carbon savings. Future crop yield improvements and technology advances, coupled with unconventional petroleum supplies, will increase biofuel carbon offsets, but clearing carbon-rich land still requires several decades or more for carbon payback. No foreseeable changes in agricultural or energy technology will be able to achieve meaningful carbon benefits if crop-based biofuels are produced at the expense of tropical forests. S Supplementary data are available from stacks.iop.org/ERL/3/034001

Trading carbon for food: Global comparison of carbon stocks vs. crop yields on agricultural land

Expanding croplands to meet the needs of a growing population, changing diets, and biofuel production comes at the cost of reduced carbon stocks in natural vegetation and soils. Here, we present a spatially explicit global analysis of tradeoffs between carbon stocks and current crop yields. The difference among regions is striking. For example, for each unit of land cleared, the tropics lose nearly two times as much carbon (∼120 tons·ha−1 vs. ∼63 tons·ha−1) and produce less than one-half the annual crop yield compared with temperate regions (1.71 tons·ha−1·y−1 vs. 3.84 tons·ha−1·y−1). Therefore, newly cleared land in the tropics releases nearly 3 tons of carbon for every 1 ton of annual crop yield compared with a similar area cleared in the temperate zone. By factoring crop yield into the analysis, we specify the tradeoff between carbon stocks and crops for all areas where crops are currently grown and thereby, substantially enhance the spatial resolution relative to previous regional estimates. Particularly in the tropics, emphasis should be placed on increasing yields on existing croplands rather than clearing new lands. Our high-resolution approach can be used to determine the net effect of local land use decisions.

Our share of the planetary pie

The rise of modern agriculture and forestry has been one of the most transformative events in human history. Whether by clearing natural ecosystems or by intensifying practices on existing croplands, pastures, and forests, human land-use activities are consuming an ever-larger share of the planets biological productivity and dramatically altering the Earths ecosystems in the process. Although the character of land use varies greatly across the world, ranging from industrialized croplands, grazing on marginal lands, managed timber lots, animal feedlots, or biofuel plantations, the ultimate outcome is the same: the production of forest or agricultural goods for human needs taken at the expense of natural ecosystems. This observation begs the question addressed in this issue of PNAS by Haberl et al. (1): Just how large is the impact of human land use on the terrestrial biosphere?

Resetting global expectations from agricultural biofuels

Aggressive renewable energy policies have helped the biofuels industry grow at a rate few could have predicted. However, while discourse on the energy balance and environmental impacts of agricultural biofuel feedstocks are common, the potential they hold for additional production has received considerably less attention. Here we present a new biofuel yield analysis based on the best available global agricultural census data. These new data give us the first opportunity to consider geographically-specific patterns of biofuel feedstock production in different regions, across global, continental, national and sub-national scales. Compared to earlier biofuel yield tables, our global results show overestimates of biofuel yields by ~100% or more for many crops. To encourage the use of regionally-specific data for future biofuel studies, we calculated complete results for 20 feedstock crops for 238 countries, states, territories and protectorates.

Ecological Footprints and Energy

biocapacity The potential productivity of the biologically productive space within a specified country, region, or territory. biologically productive space Areas of land and water capable of supporting photosynthesis at sufficient rates to provide economically useful concentrations of biomass. Marginal and unproductive regions, such as deserts, tundra, and the deep oceans, are excluded. The global biologically productive space totals 11.4 billion ha. ecological deficit The amount by which the ecological footprint of a population (e.g., a country or region) exceeds the biocapacity of the space available to that population. ecological footprint A measure of how much biocapacity a population, organization, or process requires to produce its resources and absorb its waste using prevailing technology. ecological overshoot Ecological deficit met through the overexploitation of resources or accumulation of waste. William Catton defines the term as ‘‘growth beyond an area’s carrying capacity, leading to crash.’’ embodied energy The energy used during a product’s entire life cycle for manufacture, transport, operation, and/or disposal. global hectare One hectare of biologically productive space with world-average productivity. productivity A measurement of the potential rate of biological production of a given area. Various indicators can be used to weight productivity, including agricultural suitability, potential net primary production, and useful biomass extraction.

Feeding the World and Protecting Biodiversity

Conserving biodiversity while meeting the food, feed, and fuel needs of a growing human population with changing dietary preference is one of our society’s grand challenges. Expansion and intensification that have accelerated since the 1960s has doubled crop production in many areas, but unfortunately, has come at a cost to the environment. This article summarizes the scope of agriculture, its effect on biodiversity, and strategies for feeding the world while maintaining biodiversity.

Energy Ethics in Science and Engineering Education

Substantial global changes in energy production and use are occurring at present and will continue to occur for decades to come, with widespread ramifications for the distribution of wealth and power and humanity’s social and environmental future. This raises important ethical considerations that should be addressed in the education of engineers, whose research and practice will assuredly involve energy to some degree. The Energy Ethics in Science and Engineering Education Project, funded by the U.S. National Science Foundation, sought to enhance attention to and projects in energy ethics in graduate research education concerning energy. The partners, the Consortium for Science, Policy and Outcomes (CSPO) at Arizona State University (ASU) and the Center for Engineering, Ethics, and Society (CEES) at the National Academy of Engineering (NAE), conducted a number of research, educational, and outreach activities to develop a foundational intellectual basis for understanding the ethics of energy transitions, to provide opportunities for students to learn about energy ethics, and to disseminate ideas and materials broadly. Evaluation results indicate the project has been successful in engaging students in various formats; additionally the project has illuminated a number of fundamental ideas about the interrelationships among energy, ethics, and society.