The next generation of scenarios for climate change research and assessment

Advances in the science and observation of climate change are providing a clearer understanding of the inherent variability of Earth's climate system and its likely response to human and natural influences. The implications of climate change for the environment and society will depend not only on the response of the Earth system to changes in radiative forcings, but also on how humankind responds through changes in technology, economies, lifestyle and policy. Extensive uncertainties exist in future forcings of and responses to climate change, necessitating the use of scenarios of the future to explore the potential consequences of different response options. To date, such scenarios have not adequately examined crucial possibilities, such as climate change mitigation and adaptation, and have relied on research processes that slowed the exchange of information among physical, biological and social scientists. Here we describe a new process for creating plausible scenarios to investigate some of the most challenging and important questions about climate change confronting the global community

An Analysis of Soil Respiration across Northern Hemisphere Temperate Ecosystems

Over two-thirds of terrestrial carbon is stored belowground and a significant amount of atmospheric CO₂ is respired by roots and microbes in soils. For this analysis, soil respiration (Rs) data were assembled from 31 AmeriFlux and CarboEurope sites representing deciduous broadleaf, evergreen needleleaf, grasslands, mixed deciduous/evergreen and woodland/savanna ecosystem types. Lowest to highest rates of soil respiration averaged over the growing season were grassland and woodland/savanna &lt deciduous broadleaf forests &lt evergreen needleleaf, mixed deciduous/evergreen forests with growing season soil respiration significantly different between forested and non-forested biomes (p &lt 0.001). Timing of peak respiration rates during the growing season varied from March/April in grasslands to July-September for all other biomes. Biomes with overall strongest relationship between soil respiration and soil temperature were from the deciduous and mixed forests (R⁲ ≥ 0.65). Maximum soil respiration was weakly related to maximum fine root biomass (R⁲ = 0.28) and positively related to the previous years' annual litterfall (R⁲ = 0.46). Published rates of annual soil respiration were linearly related to LAI and fine root carbon (R⁲ = 0.48, 0.47), as well as net primary production (NPP) (R⁲ = 0.44). At 10 sites, maximum growing season Rs was weakly correlated with annual GPP estimated from eddy covariance towersites (R⁲ = 0.29; p &lt 0.05), and annual soil respiration and total growing season Rs were not correlated with annual GPP (p &gt 0.1). Yet, previous studies indicate correlations on shorter time scales within site (e.g., weekly, monthly). Estimates of annual GPP from the Biome-BGC model were strongly correlated with observed annual estimates of soil respiration for six sites (R⁲ = 0.84; p &lt 0.01). Correlations from observations of Rs with NPP, LAI, fine root biomass and litterfall relate above and belowground inputs to labile pools that are available for decomposition. Our results suggest that simple empirical relationships with temperature and/or moisture that may be robust at individual sites may not be adequate to characterize soil CO₂ effluxes across space and time, agreeing with other multi-site studies. Information is needed on the timing and phenological controls of substrate availability (e.g., fine roots, LAI) and inputs (e.g., root turnover, litterfall) to improve our ability to accurately quantify the relationships between soil CO₂ effluxes and carbon substrate storage

Microstructures and Stabilization Mechanisms of Nanocrystalline Iron-Chromium Alloys with Hafnium Addition

The low thermal stability of nanocrystalline metals severely limits their applications at high temperatures. In this study, we investigate the nanocrystalline stabilization mechanisms for Fe-14Cr alloys with 1, 2, and 4 at. pct Hf addition at 1173 K (900 °C). Microstructural characterizations using aberration-corrected scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy reveal high density of HfO2 nanoparticles with sizes of ~4 nm dispersed throughout the ferritic matrix. This indicates that kinetic stabilization by HfO2 nanoparticle pinning is primarily responsible for the observed high thermal stability. In addition, some Hf and Cr segregation on grain boundaries is observed in the Fe-14Cr-4Hf, suggesting the existence of thermodynamic stabilization at high Hf content. Second-phase precipitations such as hafnium carbide, M23C6, and Fe-Cr-Hf intermetallic phase are also found in the Fe-14Cr-4Hf, but their large sizes and inter-spacing suggest that their contribution to stabilization is minimal