Expert assessment of vulnerability of permafrost carbon to climate change

Approximately 1700 Pg of soil carbon (C) are stored in the northern circumpolar permafrost zone, more than twice as much C than in the atmosphere. The overall amount, rate, and form of C released to the atmosphere in a warmer world will influence the strength of the permafrost C feedback to climate change. We used a survey to quantify variability in the perception of the vulnerability of permafrost C to climate change. Experts were asked to provide quantitative estimates of permafrost change in response to four scenarios of warming. For the highest warming scenario (RCP 8.5), experts hypothesized that C release from permafrost zone soils could be 19–45 Pg C by 2040, 162–288 Pg C by 2100, and 381–616 Pg C by 2300 in CO₂ equivalent using 100-year CH₄ global warming potential (GWP). These values become 50 % larger using 20-year CH₄ GWP, with a third to a half of expected climate forcing coming from CH₄ even though CH₄ was only 2.3 % of the expected C release. Experts projected that two-thirds of this release could be avoided under the lowest warming scenario (RCP 2.6). These results highlight the potential risk from permafrost thaw and serve to frame a hypothesis about the magnitude of this feedback to climate change. However, the level of emissions proposed here are unlikely to overshadow the impact of fossil fuel burning, which will continue to be the main source of C emissions and climate forcing.     

Recent advances in understanding ice sheet dynamics

Glaciers and ice sheets play a dynamic role in Earth's climate system, influencing regional- and global-scale climate and responding to climate change on time scales from years to millennia. They are also an integral part of Earth's landscape in alpine and polar regions, where they are an active agent in isostatic, tectonic, and Earth surface processes. This review paper summarizes recent progress in understanding and modelling ice sheet dynamics, from the microphysical processes of ice deformation in glaciers to continental-scale processes that influence ice dynamics. Based on recent insights and research directions, it can be expected that a new generation of ice sheet models will soon replace the current standard. Improvements that can be foreseen in the near future include: (i) the addition of internally-consistent evolutionary equations for ice crystal fabric (anisotropic flow laws), (ii) more generalized flow laws that include different deformation mechanisms under different stress regimes, (iii) explicit incorporation of the effects of chemical impurities and grain size (dynamic recrystallization) on ice deformation, (iv) higher-order stress solutions to the momentum balance (Stokes' equation) that governs ice sheet flow, and (v) the continued merger of ice sheet models with increasingly complex Earth systems models, which include fully-coupled subglacial hydrological and geological processes. Examples from the Greenland Ice Sheet and Vatnajökull Ice Cap, Iceland are used to illustrate several of these new directions and their importance to glacier dynamics.     

Making seed systems more resilient to stress

While seed security is key to food security, concrete means for building resilient seed systems remain unexplored in research and practice. A new toolkit, the Seed System Security Assessment (SSSA), examines what actually happens to seed systems during crises and highlights specific features that foster or undermine resilience. Drawing evidence from SSSAs in contexts of political and civil conflict (Zimbabwe and South Sudan), earthquake (Haiti) and drought (Kenya), the article shows that seed systems prove to be relatively resilient, at least in terms of meeting farmers’ planting needs for the upcoming season. Altering crop profiles, making use of multiple delivery channels, and innovating (for example, with new barter mechanisms) all become key, as does mobilizing cross-scale seed supply linkages. However, despite short-term survival, in the medium term, both formal and informal seed systems will have to be transformed to address agro-ecological and farming system challenges, partially shaped by global environmental changes. Key is that formal seed systems will play a catalytic but supporting role, with the onus on resilience response lying within informal systems, and especially with local markets and their traders. Also key is that achieving seed security in fluctuating environments will hinge on developing resilience-linked information systems which put as much weight on helping farmers strategize as on delivering the planting material itself. The article defines seed system resilience, identifies eight principles linked to processes that build such resilience, and makes 15 practical recommendations for enhancing seed system resilience in the short and medium term. Finally, drawing insights from seed systems, processes central for building resilience in other development sectors are highlighted.     

Exceptionally Long MTBE Plumes of the Past Have Greatly Diminished

Studies published in the late 1990s and early 2000s identified the presence of exceptionally long methyl tert‐butyl ether (MTBE) plumes (more than 600 m or 2000 feet) in groundwater and have been cited in technical literature as characteristic of MTBE plumes. However, the scientific literature is incomplete in regard to the subsequent behavior and fate of these MTBE plumes over the past decade. To address this gap, this issue paper compiles recent groundwater monitoring records for nine exceptional plumes that were identified in prior studies. These nine sites exhibited maximum historical MTBE groundwater plume lengths ranging from 820 m (2700 feet) to 3200 m (10,500 feet) in length, exceeding the lengths of 99% of MTBE plumes, as characterized in multiple surveys at underground storage tank sites across the United States. Groundwater monitoring data compiled in our review demonstrate that these MTBE plumes have decreased in length over the past decade, with five of the nine plumes exhibiting decreases of 75% or more compared to their historical maximum lengths. MTBE concentrations within these plumes have decreased by 93% to 100%, with two of the nine sites showing significant decreases (98% and 99%) such that the regulatory authority has subsequently designated the site as requiring no further action.     

Pasture, profit, and power: An environmental history of cattle ranching in Colombia, 1850-1950

This article examines the expansion of cattle ranching from 1850 to 1950 into lowland forests of Colombia. Although most attention to ranching as a source of deforestation in Latin America has focused on the second half of the 20th century, in Colombia it has a much longer history. The article also examines the role of introduced African grasses in the process of pasture development. While it discusses their ability to suppress secondary-forest regeneration, it underscores their contribution to productivity gains to help explain their wide diffusion. Lastly, the article suggests that paying greater attention to the costs and labor of pasture formation can serve as a springboard to reexamine a number of common stereotypes about ranching: that the logic of livestock was not about producing beef; that cattle were primarily a means to control territory; and that ranching ‘profits’ stemmed from extra-economic sources. Although there is some truth to these explanations, the dominance of cattle throughout the countryside cannot be explained without taking the economic and productive logic of ranching into account. This, in turn, should also help push us to better understand the nature of landed power and the dynamics of agrarian change in Colombia.     

Forecasting volcanic events: some contemporary issues

As the regions around active volcanoes succumb to large increases in population, particularly in the developing world where most of the high-risk volcanoes are located, the threat posed by eruptions becomes increasingly serious. Improvements in eruption forecasting are critical to combat this situation, for reducing injury and loss of life, and for minimizing the detrimental effects to local economies and to the fabric of society. Better-constrained forecasts are strongly dependent on geophysical and other data gathered during a program of volcano surveillance, and we reveal how, if interpreted in terms of static rock fracturing, analysis of changes in volcanic seismicity and ground deformation may be used to forecast more accurately the onset of eruptive activity. As illustrated by recent events at several volcanoes, studies of previous activity, increased levels of monitoring, and improved training of scientists are also all crucial to improving forecasts of impending eruptions.     

A spatial approach to select pilot counties for programs to correct the biased sex ratio at birth in Shandong province,China

The highly skewed sex ratio at birth (SRB) in China has stimulated numerous studies. However, the geographic distribution of SRB is seldom investigated, particularly at the county level. The need for an understanding at this level has increased since the Chinese government initiated its ‘Care for Girls’ campaign to improve the survival rate of females. This campaign has been initiated in a set of pilot counties. In this article we assess the effectiveness of the set of pilot counties in Shandong province and propose two alternate configurations. To do this, we first assess the spatial distribution of the SRB values by county in Shandong, expressed as a z-score (zSRB) after correcting for the biologically expected SRB value and population size of zero-aged children. A local Moran's I_i analysis of the zSRB values indicates a significant high–high cluster in the southwest of the province. The I_i , zSRB and female deficit (the difference of the observed from biologically expected number of zero-aged females) were then used to define two alternate configurations for the pilot counties. A comparison of the current and alternate configurations against a Monte Carlo randomisation analysis shows that the current configuration is significantly different from a random selection (p < 0.05) for the two criteria of maximising the aggregate female deficit and maximising the zSRB. Although this is a good result, both alternate configurations were more significant (p < 0.001), and therefore represent potentially better configurations for the campaign given the criteria used. The spatial analysis approach developed here could be used to improve the effectiveness of the Care-for-Girls campaign in Shandong province, and elsewhere in China.     

Evolution of the etna volcano: Information from the southern wall of the Valle Del Bove Caldera

The greater part of Etna can be regarded as a complex strato-shield volcano constructed from the overlapping products of several centres of trachy-basaltic activity. The Valle del Bove is a horse-shoe-shaped caldera, 8 km long and 5 km wide, cut into the eastern flanks of Etna. The caldera is one of the few areas on the volcano where historic eruptions have not obscured the products of pre-historic centres of activity and these are well exposed in the cliff walls surrounding the caldera. Examination of these older volcanics provides important information on the eruptive style and internal plumbing of the Etna volcano during pre-historic times, and suggests that both were significantly different from the present day.Much of the southern wall of the Valle del Bove represents a surviving portion of the Trifoglietto II volcano, the largest pre-historic centre of activity. A stratigraphy is constructed for the southern wall, the Trifoglietto II lavas and pyroclastics rest unconformably upon the eroded remnants of an older centre, and are themselves overlain by the products of younger centres. All the lavas exposed in the southern wall are of alkalic affinity and comprise a trachybasaltic suite ranging from hawaiite to benmoreite. Variation in the chemistry of the lavas can be explained by their differentiation at high levels in the crust from a more basic magma of alkali olivine-basalt/hawaiite composition. An anomalous trend in the TiO₂ content of the Trifoglietto II lavas may be explained by the fractionation of kaersutite (Ti-rich amphibole).A study has been made of the numerous dykes exposed in the walls of the Valle del Bove, the alignments of which parallel trends which are important on Etna at the present time.It is proposed that the initial opening of the Valle del Bove occurred sometime between 20,000 and 10,000 y. B.P., as a result of a phreatic or phreato-magmatic explosion near the base of the eastern flank of Trifoglietto II. This is visualised as triggering a slope failure and resulting in the destruction of much of the centre by a catastrophic landslide. This mechanism has much in common with the explosive eruptions which produced both the Bandai-san (Japan) caldera in 1888, and the Mount St Helens caldera in May, 1980.