Can radiative forcing be limited to 2.6 Wm−2 without negative emissions from bioenergy AND CO2 capture and storage?

Combining bioenergy and carbon dioxide (CO₂) capture and storage (CCS) technologies (BECCS) has the potential to remove CO₂ from the atmosphere while producing useful energy. BECCS has played a central role in scenarios that reduce climate forcing to low levels such as 2.6 Wm^?2. In this paper we consider whether BECCS is essential to limiting radiative forcing (RF) to 2.6 Wm^?2 by 2100 using the Global Change Assessment Model, a closely coupled model of biogeophysical and human Earth systems. We show that BECCS can potentially reduce the cost of limiting RF to 2.6 Wm^?2 by 2100 but that a variety of technology combinations that do not include BECCS can also achieve this goal, under appropriate emissions mitigation policies. We note that with appropriate supporting land-use policies terrestrial sequestration could deliver carbon storage ranging from 200 to 700 PgCO₂-equiavalent over the 21st century. We explore substantial delays in participation by some geopolitical regions. We find that the value of BECCS is substantially higher under delay and that delay results in higher transient RF and climate change. However, when major regions postponed mitigation indefinitely, it was impossible to return RF to 2.6 Wm^?2 by 2100. Neither finite land resources nor finite potential geologic storage capacity represented a meaningful technical limit on the ability of BECCS to contribute to emissions mitigation in the numerical experiments reported in this paper.     

Mine Overburden Dump Failure: A Case Study

In any open cast mine, the management of stripped spoil during mining is crucial to the mine’s successful operation. The improper management of the overburden (OB) dump can result in stability issues which may affect safety and production of the mine. Various literatures have reported the failure of open pit dumps and the consequences in loss of life, production and impact on neighbouring amenities. Recently, the failure of an out-of-pit OB dump at an Indian Colliery was reported. The failed OB dump displaced spoil approximately 70 m from the original location of the dump toe and impacted on neighbouring amenities. This paper back analyse material properties and investigates the probable mechanism of this OB failure. Well established tools including limiting equilibrium and continuum numerical methods have been used to understand and identify the failure kinematics of this dump. It has been found that the residual friction angle of the material comprising the dump structural unit dominates stability. Mobilisation of residual strength can occur by operational induced strains and/or the presence of water. The shear strength of the foundation was fully mobilised and provided a slip surface for the overlying dump material. The resultant failure is manifest as a bilinear wedge movement of two ridged blocks defined by linear rupture planes.     

Synthesizing multifaceted characterization techniques to refine a conceptual model of groundwater sources to springs in valley settings (Minnesota,USA)

Springs are commonly used as low-cost monitoring locations to assess groundwater quality and long-term trends. However, spring waters in many settings are a mixture of groundwater sources that range in physical properties and water chemistry. The objective of this work was to determine water sources of springs emerging from the North American midcontinent Cambrian-Ordovician aquifer system at a fish hatchery near Lanesboro, Minnesota (USA), and compare and contrast the sources to shallower and deeper sources. The hydrology of the Lanesboro State Fish Hatchery has been studied for decades using a combination of dye tracing, thermal monitoring, geochemical sampling, and nearby borehole and outcrop observations. Previous studies are integrated with recently collected dye tracing results and geochemical data to develop a comprehensive conceptual model of groundwater flow. Dye trace findings and geochemistry indicate well-developed karst and bedrock fractures in shallowly buried unconfined carbonate formations are important transport pathways to convey anthropogenically influenced waters from the land surface to the hatchery springs. However, borehole dye traces, thermal monitoring, continuous nitrate monitoring, and mixing calculations show that a deeper confined siliciclastic aquifer is responsible for delivering relatively pristine water that accounts for about half of hatchery spring flux. Characterization of the hatchery’s groundwater systems provides fishery managers with information to protect this vital resource and improved context to interpret water-quality-monitoring data that track agricultural contaminants. The methods and results of this study may be widely applicable across a large extent of the Cambrian-Ordovician aquifer system, and to multiaquifer sedimentary bedrock systems elsewhere.

     

Trade-offs of different land and bioenergy policies on the path to achieving climate targets

Many papers have shown that bioenergy and land-use are potentially important elements in a strategy to limit anthropogenic climate change. But, significant expansion of bioenergy production can have a large terrestrial footprint. In this paper, we test the implications for land use, the global energy system, emissions and mitigation costs of meeting a specific climate target, using a single fossil fuel and industrial sector policy instrument, but with five alternative bioenergy and land-use policy architectures. These scenarios are illustrative in nature, and designed to explore trade-offs. We find that the policies we examined have differing effects on the different segments of the economy. Comprehensive land policies can reduce land-use change emissions, increasing allowable emissions in the energy system, but have implications for the cost of food. Bioenergy penalties and constraints, on the other hand, have little effect on food prices, but result in less bioenergy and thus can increase mitigation costs and energy prices.     

A dynamic riparian forest structure model for predicting large wood inputs to meandering rivers

Fluvial processes strongly influence riparian forests through rapid and predictable shifts in dominant species, tree density and size that occur in the decades following large floods. Modelling riparian forest characteristics based on the age and evolution of floodplains is useful in predicting ecosystem functions that depend on the size and density of trees, including large wood delivered to river channels, forest biomass and habitat quality. We developed a dynamic model of riparian forest structure that predicts changes in tree size and density using floodplain age derived from air photos and historical maps. Using field data and a riparian forest chronosequence for the 160-km middle reach of the Sacramento River (California, USA), we fit Weibull diameter distributions with time-varying parameters to the empirical data. Species were stratified into early and late successional groups, each with time-varying functions of tree density and diameter distributions. From these, we modelled how the number and size of trees in a stand changed throughout forest succession, and evaluated the goodness-of-fit of model predictions. Model outputs for the early successional group, composed primarily of cottonwoods and willows, accounted for most of the stand basal area and large trees >10 cm DBH for the first 50 years. Post-pioneer species with slower growth had initially low densities that increased slowly from the time of floodplain creation. Within the first 100 years, early successional trees contributed the most large wood that could influence fluvial processes, carbon storage, and instream habitat. We applied the model to evaluate the potential large wood inputs to the middle Sacramento River under a range of historical bank migration rates. Going forward, this modelling approach can be used to predict how riparian forest structure and other ecosystem benefits such as carbon sequestration and habitat quality respond to different river management and restoration actions.     

Trace analysis of hydrocarbons in coral cores from Saudi Arabia

As part of a long-term environmental assessment of the impact of the 1991 Gulf War on coral reefs, the Australian Institute of Marine Science (AIMS) conducted growth and chemistry studies on coral cores from the Arabian Gulf. Twenty-eight cores were collected from four coral reefs located offshore from Saudi Arabia.Annual coral growth bands surrounding the 1991 oil spill were analysed in selected cores. Additionally, in cores that extended to the early 1980s, annual layers from 1980 to 1986 were analysed for possible residues from the 1983–4 oil spill caused by the Nowruz oil field blowout during the Iraq–Iran war. Both major spill events were targeted to provide additional confidence in relating oil concentrations to specific pollution events. We detected petroleum biomarkers in several coral annual bands related to the major pollution events. However, the oil remaining in these cores has been altered over time and the biomarker ratios found in these oil residues differed from Gulf crude oils.The concentrations of hydrocarbons were compared with the growth parameters of the coral cores. Only one sample may have recorded an “impact” of oil exposure. There was no other correspondence between slight changes in growth parameters between years and the trace chemistry. Therefore, chemical analysis enabled detection of the exposure incident, but provided no insight into the amount of oil to which the coral had been exposed. The chemical data can only infer biological impact if growth was significantly decreased.The average coral growth characteristics of Porites from the four sites in the Arabian Gulf were normal, as predicted from the average water temperatures of the region. There was an indication of an overall decline in growth over time, which should be monitored in the future.     

Contrasting stratified plutons exposed in tilt blocks, Eldorado Mountains, Colorado River Rift, NV, USA

Roof-to-floor exposures of mid-Miocene plutons in tilt blocks south of Las Vegas, NV, reveal distinct but strongly contrasting magma chamber statigraphy. The Searchlight and Aztec Wash plutons are well-exposed, stratified intrusions that show a similar broad range in composition from 45–75 wt.% SiO₂. Homogeneous granites that comprise about one-third of each intrusion are virtually identical in texture and elemental and isotopic chemistry. Mafic rocks that are present in both plutons document basaltic input into felsic magma chambers. Isotopic compositions suggest that mafic magmas were derived from enriched lithospheric mantle with minor crustal contamination, whereas more felsic rocks are hybrids that are either juvenile basaltic magma+crustal melt mixtures or products of anatexis of ancient crust+young (Mesozoic or Miocene?) mafic intraplate.

Despite general similarities, the two plutons differ markedly in dimensions and lithologic stratigraphy. The Searchlight pluton is much thicker (10 vs. 3 km) and has thick quartz monzonite zones at its roof and floor that are absent in the Aztec Wash pluton. Isotopic and elemental data from Searchlight pluton suggest that the upper and lower zones are cogenetic with the granite; we interpret the finer grained, slightly more felsic upper zone to represent a downward migrating solidification front and the lower zone to be cumulate. In contrast, the upper part of the Aztec Wash pluton is granite, and a heterogeneous, mafic-rich injection zone with distinct isotopic chemistry forms the lower two-thirds of the intrusion. Similar mafic rocks are relatively sparse in Searchlight pluton and do not appear to have played a central role in construction of the pluton. Large felsic and composite dikes that attest to repeated recharging and intrachamber magma transfer are common in the Aztec Wash pluton but absent in the Searchlight pluton. Thus, although both intrusions were filled by similar magmas and both developed internal stratification, the two intrusions evolved very differently. The distinctions may be attributable to scale and resulting longevity and/or to subtle differences in tectonic setting.     

Implications of weak near-term climate policies on long-term mitigation pathways

While the international community has agreed on the long-term target of limiting global warming to no more than 2 °C above pre-industrial levels, only a few concrete climate policies and measures to reduce greenhouse gas (GHG) emissions have been implemented. We use a set of three global integrated assessment models to analyze the implications of current climate policies on long-term mitigation targets. We define a weak-policy baseline scenario, which extrapolates the current policy environment by assuming that the global climate regime remains fragmented and that emission reduction efforts remain unambitious in most of the world’s regions. These scenarios clearly fall short of limiting warming to 2 °C. We investigate the cost and achievability of the stabilization of atmospheric GHG concentrations at 450 ppm CO₂e by 2100, if countries follow the weak policy pathway until 2020 or 2030 before pursuing the long-term mitigation target with global cooperative action. We find that after a deferral of ambitious action the 450 ppm CO₂e is only achievable with a radical up-scaling of efforts after target adoption. This has severe effects on transformation pathways and exacerbates the challenges of climate stabilization, in particular for a delay of cooperative action until 2030. Specifically, reaching the target with weak near-term action implies (a) faster and more aggressive transformations of energy systems in the medium term, (b) more stranded investments in fossil-based capacities, (c) higher long-term mitigation costs and carbon prices and (d) stronger transitional economic impacts, rendering the political feasibility of such pathways questionable.