The Northwest Africa (NWA) 5790 meteorite: A mesostasis‐rich nakhlite with little or no Martian aqueous alteration

Northwest Africa (NWA) 5790 is the most recently discovered member of the nakhlite group. Its mineralogy differs from the other nakhlites with a high abundance mesostasis (38.1 ± 3.6 vol%) and scarcity of olivine (4.0 ± 2.2 vol%). Furthermore, zoning of augite phenocrysts, and other petrographic and chemical characteristics suggest that NWA 5790 samples the chilled margin of its parent lava flow/sill. NWA 5790 contains calcite and rare clay minerals that are evidence for its exposure to liquid water. The calcite forms a cement to coatings of dust on the outer surface of the find and extends into the interior of the meteorite within veins. The presence of microbial remains within the coating confirms that the dust and its carbonate cement are terrestrial in origin, consistent with the carbon and oxygen isotope composition of the calcite. The clay minerals are finely crystalline and comprise ~0.003 vol% of the meteorite. δD values of the clay minerals range from ?212 ± 109‰ to ?96 ± 132‰, and cannot be used to distinguish between a terrestrial or Martian origin. As petrographic results are also not definitive, we conclude that secondary minerals produced by Martian groundwaters are at best very rare within NWA 5790. The meteorite has therefore sampled a region of the lava flow/sill with little or no exposure to the aqueous solutions that altered other nakhlites. This isolation could relate to the scarcity of olivine in NWA 5790 because dissolution of olivine in other nakhlites by Martian groundwaters enhanced their porosity and permeability, and provided solutes for secondary minerals.     

Probabilistic estimates of future changes in California temperature and precipitation using statistical and dynamical downscaling

Sixteen global general circulation models were used to develop probabilistic projections of temperature (T) and precipitation (P) changes over California by the 2060s. The global models were downscaled with two statistical techniques and three nested dynamical regional climate models, although not all global models were downscaled with all techniques. Both monthly and daily timescale changes in T and P are addressed, the latter being important for a range of applications in energy use, water management, and agriculture. The T changes tend to agree more across downscaling techniques than the P changes. Year-to-year natural internal climate variability is roughly of similar magnitude to the projected T changes. In the monthly average, July temperatures shift enough that that the hottest July found in any simulation over the historical period becomes a modestly cool July in the future period. Januarys as cold as any found in the historical period are still found in the 2060s, but the median and maximum monthly average temperatures increase notably. Annual and seasonal P changes are small compared to interannual or intermodel variability. However, the annual change is composed of seasonally varying changes that are themselves much larger, but tend to cancel in the annual mean. Winters show modestly wetter conditions in the North of the state, while spring and autumn show less precipitation. The dynamical downscaling techniques project increasing precipitation in the Southeastern part of the state, which is influenced by the North American monsoon, a feature that is not captured by the statistical downscaling.     

Quantitative evaluation of the seasonal variations in climate model cloud regimes

An extended cloud-clustering method to assess the seasonal variation of clouds is applied to five CMIP5 models. The seasonal variation of the total cloud radiative effect (CRE) is dominated by variations in the relative frequency of occurrence of the different cloud regimes. Seasonal variations of the CRE within the individual regimes contribute much less. This is the case for both observations, models and model errors. The error in the seasonal variation of cloud regimes, and its breakdown into mean amplitude and time varying components, are quantified with a new metric. The seasonal variation of the CRE of the cloud regimes is relatively well simulated by the models in the tropics, but less well in the extra-tropics. The stratocumulus regime has the largest seasonal variation of shortwave CRE in the tropics, despite having a small magnitude in the climatological mean. Most of the models capture the temporal variation of the CRE reasonably well, with the main differences between models coming from the variation in amplitude. In the extra-tropics, most models fail to correctly represent both the amplitude and time variation of the CRE of congestus, frontal and stratocumulus regimes. The annual mean climatology of the CRE and its amplitude in the seasonal variation are both underestimated for the anvil regime in the tropics, the cirrus regime and the congestus regime in the extra-tropics. The models in this study that best capture the seasonal variation of the cloud regimes tend to have higher climate sensitivities.     

The challenge to detect and attribute effects of climate change on human and natural systems

Future scenarios of the energy system under greenhouse gas emission constraints depict dramatic growth in a range of energy technologies. Technological growth dynamics observed historically provide a useful comparator for these future trajectories. We find that historical time series data reveal a consistent relationship between how much a technology’s cumulative installed capacity grows, and how long this growth takes. This relationship between extent (how much) and duration (for how long) is consistent across both energy supply and end-use technologies, and both established and emerging technologies. We then develop and test an approach for using this historical relationship to assess technological trajectories in future scenarios. Our approach for “learning from the past” contributes to the assessment and verification of integrated assessment and energy-economic models used to generate quantitative scenarios. Using data on power generation technologies from two such models, we also find a consistent extent - duration relationship across both technologies and scenarios. This relationship describes future low carbon technological growth in the power sector which appears to be conservative relative to what has been evidenced historically. Specifically, future extents of capacity growth are comparatively low given the lengthy time duration of that growth. We treat this finding with caution due to the low number of data points. Yet it remains counter-intuitive given the extremely rapid growth rates of certain low carbon technologies under stringent emission constraints. We explore possible reasons for the apparent scenario conservatism, and find parametric or structural conservatism in the underlying models to be one possible explanation.     

PM2.5 co-benefits of climate change legislation part 2: California governor’s executive order S-3-05 applied to the transportation sector

California Governor’s Executive Order (CGEO) S-3-05 requires that California greenhouse gas (GHG) emissions be reduced to 80 % below 1990 levels by the year 2050. Meeting this target will require drastic changes in transportation technology, fuel, and behavior which will reduce criteria pollutant emissions as well as GHG emissions. The improvement to local air quality caused by the reduced criteria pollutant emissions must be calculated to fully evaluate the overall benefits and costs of CGEO S-3-05. In the present study, seven different transportation scenarios that move towards the goals of CGEO S-3-05 in the transportation sector were examined to determine how they would affect future airborne particulate matter (PM_2.5) concentrations in California: (1) hydrogen fuel cells, (2) electric vehicles, (3) high efficiency vehicles, (4) public mass transit, (5) biofuels, (6) biofuels + hybrid electric vehicles, and (7) hydrogen fuel cells + electric vehicles. The air quality implications of each scenario were evaluated using a chemical transport model applied during a wintertime stagnation episode representing future climate in California. Scenarios (6) and (7) reduced population-weighted PM_2.5 mass concentrations by ~9 % and PM_2.5 elemental carbon (EC) concentrations by ~30 % relative to base-case predictions.     

Estimating environmentally relevant fixed nitrogen demand in the 21st century

Human activities affect the impact of the nitrogen cycle on both the environment and climate. The rate of anthropogenic nitrogen fixation from atmospheric N₂ may serve as an indicator to the magnitude of this impact, acknowledging that relationship to be effect-dependent and non-linear. Building on the set of Representative Concentration Pathway (RCP) scenarios developed for climate change research, we estimate anthropogenic industrial nitrogen fixation throughout the 21st century. Assigning characteristic key drivers to the four underlying scenarios we arrive at nitrogen fixation rates for agricultural use of 80 to 172 Tg N/yr by 2100, which is slightly less to almost twice as much compared with the fixation rate for the year 2000. We use the following key drivers of change, varying between scenarios: population growth, consumption of animal protein, agricultural efficiency improvement and additional biofuel production. Further anthropogenic nitrogen fixation for production of materials such as explosives or plastics and from combustion are projected to remain considerably smaller than that related to agriculture. While variation among the four scenarios is considerable, our interpretation of scenarios constrains the option space: several of the factors enhancing the anthropogenic impact on the nitrogen cycle may occur concurrently, but never all of them. A scenario that is specifically targeted towards limiting greenhouse gas emissions ends up as the potentially largest contributor to nitrogen fixation, as a result of large amounts of biofuels required and the fertilizer used to produce it. Other published data on nitrogen fixation towards 2100 indicate that our high estimates based on the RCP approach are rather conservative. Even the most optimistic scenario estimates that nitrogen fixation rate will remain substantially in excess of an estimate of sustainable boundaries by 2100.     

A return to wet conditions over Africa: 1995–2010

Climatic trends over sub-Saharan Africa are described using major river flows, European Community Medium-Range Weather Forecasts, Coupled Forecast System, global land surface data assimilation and National Center for Environmental Prediction reanalysis, Global Precipitation Climate Center gauge data, and satellite observations in the period 1995–2010. The Niger and Zambezi rivers reached flow levels last seen in the 1950s (2,000 and 5,000 m³ s^?1, respectively), and rainfall across the Congo Basin increased steadily ~+0.16 mm day^?1 year^?1. Weather events that contributed to flooding are studied and include the Zambezi tropical trough of 4 January 2008 and the Sahelian easterly wave of 19 July 2010. Diurnal summer rainfall increased threefold over the 1995–2010 period in conjunction with a strengthened land–sea temperature contrast, onshore flow, and afternoon uplift. 700 mb zonal winds over East Africa became easterly after 2001, so clean Indian Ocean air was entrained to the Congo, improving convective efficiency. Relationships between the African monsoon circulation and global teleconnections are explored. Zonal wind convergence around the Congo appears related with the tropical multi-decadal oscillation and signals in the Atlantic during the study period.     

Encouraging clean energy investment in developing countries: what role for aid?

A large portion of foreign assistance for climate change mitigation in developing countries is directed to clean energy facilities. To support international mitigation goals, however, donors must make investments that have effects beyond individual facilities. They must reduce barriers to private-sector investment by generating information for developers, improving relevant infrastructure, or changing policies. We examine whether donor agencies target financing for commercial-scale wind and solar facilities to countries where private investment in clean energy is limited and whether donor investments lead to more private investments. On average, we find no positive evidence for these patterns of targeting and impact. Coupled with model results that show feed-in tariffs increase private investment, we argue that donor agencies should reallocate resources to improve policies that promote private investment in developing countries, rather than finance individual clean energy facilities.

Policy relevance

We suggest that international negotiations could usefully shift the focus of climate change finance towards adaptation in exchange for mitigation-improving policy reforms in developing countries. There is little evidence that mitigation-related financing is having broader effects on energy production, so new financial arrangements should be the focus of future negotiations. Additionally, international donors should focus efforts on reforming policies to attract private investment.     

The High-Resolution Coronal Imager (Hi-C)

The High-Resolution Coronal Imager (Hi-C) was flown on a NASA sounding rocket on 11 July 2012. The goal of the Hi-C mission was to obtain high-resolution (≈?0.3?–?0.4′′), high-cadence (≈?5 seconds) images of a solar active region to investigate the dynamics of solar coronal structures at small spatial scales. The instrument consists of a normal-incidence telescope with the optics coated with multilayers to reflect a narrow wavelength range around 19.3 nm (including the Fe xii 19.5-nm spectral line) and a 4096×4096 camera with a plate scale of 0.1′′?pixel^?1. The target of the Hi-C rocket flight was Active Region 11520. Hi-C obtained 37 full-frame images and 86 partial-frame images during the rocket flight. Analysis of the Hi-C data indicates the corona is structured on scales smaller than currently resolved by existing satellite missions.