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Stabilizing the carbon dioxide-induced component of climate change is an energy problem. Establishment of a course toward such stabilization will require the development within the coming decades of primary energy sources that do not emit carbon dioxide to the atmosphere, in addition to efforts to reduce end-use energy demand. Mid-century primary power requirements that are free of carbon dioxide emissions could be several times what we now derive from fossil fuels (~[10.sup.13] watts), even with improvements in energy efficiency. Here we survey possible future energy sources, evaluated for their capability to supply massive amounts of carbon emission-free energy and for their potential for large-scale commercialization. Possible candidates for primary energy sources include terrestrial solar and wind energy, solar power satellites, biomass, nuclear fission, nuclear fusion, fission-fusion hybrids, and fossil fuels from which carbon has been sequestered. Non-primary power technologies that could contribute to climate stabilization include efficiency improvements, hydrogen production, storage and transport, superconducting global electric grids, and geoengineering. All of these approaches currently have severe deficiencies that limit their ability to stabilize global climate. We conclude that a broad range of intensive research and development is urgently needed to produce technological options that can allow both climate stabilization and economic development., More than a century ago, Arrhenius put forth the idea that C[O.sub.2] from fossil fuel burning could raise the infrared opacity of the atmosphere enough to warm Earth (1). In [...]

A land process model, Integrated Science Assessment Model, is extended to simulate contemporary soybean and maize crop yields accurately and changes in yields over the period 1901–2100 driven by environmental factors (atmospheric CO2 level ([CO2]) and climate), and management factors (nitrogen input and irrigation). Over the twentieth century, each factor contributes to global yield increase; increasing nitrogen fertilization rates is the strongest driver for maize, and increasing [CO2] is the strongest for soybean. Over the 21st century, crop yields are projected under two future scenarios, RCP4.5-SSP2 and RCP8.5-SSP5; the warmer temperature drives yields lower, while rising [CO2] drives yields higher. The adverse warmer temperature effect of maize and soybean is offset by other drivers, particularly the increase in [CO2], and resultant changes in the phenological events due to climate change, particularly planting dates and harvesting times, by 2090s under both scenarios. Global yield for maize increases under RCP4.5-SSP2, which experiences continued growth in [CO2] and higher nitrogen input rates. For soybean, yield increases at a similar rate. However, in RCP8.5-SSP5, maize yield declines because of greater climate warming, extreme heat stress conditions, and weaker nitrogen fertilization than RCP4.5-SSP2, particularly in tropical and subtropical regions, suggesting that application of advanced technologies, and stronger management practices, in addition to climate change mitigation, may be needed to intensify crop production over this century. The model also projects spatial variations in yields; notably, the higher temperatures in tropical and subtropical regions limit photosynthesis rates and reduce light interception, resulting in lower yields, particularly for soybean under RCP8.5-SSP5. [ABSTRACT FROM AUTHOR]

The land process model, ISAM, is extended to accurately simulate contemporary soybean and maize crop yields, and estimate changes in yield over the period 1901-2100 driven by past and future changes in environmental factors -atmospheric CO2 level ([CO2]) and climate (temperature and precipitation) -- and management factors -- nitrogen fertilizer and deposition, irrigation, and crop harvest areas. Over the 20th century, each of these factors contributes to the increase in global crop yield with increasing nitrogen fertilizer application the strongest of these drivers for maize and increasing [CO2] the strongest for soybean. Over the 21st century, two future scenarios -- RCP4.5-SSP2 and RCP8.5-SSP5 -- of the environmental and management factors are modeled to estimate their influence on future crop yield. For both crops under both scenarios, changing climate drives yield lower, while rising [CO2] drives yield higher. For soybean, the negative climate effect is more than offset by the other drivers -- particularly the increase in [CO2] -- leading to an increase in global soybean yield by the 2090s. For maize, combined negative climate and harvest area effects are offset in RCP4.5-SSP2, which has continued growth in nitrogen fertilizer application, leaving global yield roughly unchanged. However, in RCP8.5-SSP5 maize yield declines since this scenario has greater warming of climate and weaker nitrogen fertilizer application than RCP4.5-SSP2. The model also projects differences between geographical regions; notably, higher temperatures in tropical regions limit photosynthesis rates and reduce light interception by accelerating phenological development in both crops, particularly for RCP8.5-SSP5 and for soybean. [ABSTRACT FROM AUTHOR]