Age and context of the oldest known hominin fossils from Flores.

Recent excavations at the early Middle Pleistocene site of Mata Menge in the So'a Basin of central Flores, Indonesia, have yielded hominin fossils attributed to a population ancestral to Late Pleistocene Homo floresiensis. Here we describe the age and context of the Mata Menge hominin specimens and associated archaeological findings. The fluvial sandstone layer from which the in situ fossils were excavated in 2014 was deposited in a small valley stream around 700 thousand years ago, as indicated by (40)Ar/(39)Ar and fission track dates on stratigraphically bracketing volcanic ash and pyroclastic density current deposits, in combination with coupled uranium-series and electron spin resonance dating of fossil teeth. Palaeoenvironmental data indicate a relatively dry climate in the So'a Basin during the early Middle Pleistocene, while various lines of evidence suggest the hominins inhabited a savannah-like open grassland habitat with a wetland component. The hominin fossils occur alongside the remains of an insular fauna and a simple stone technology that is markedly similar to that associated with Late Pleistocene H. floresiensis.

Negative emissions technologies and carbon capture and storage to achieve the Paris Agreement commitments.

How will the global atmosphere and climate be protected? Achieving net-zero CO2 emissions will require carbon capture and storage (CCS) to reduce current GHG emission rates, and negative emissions technology (NET) to recapture previously emitted greenhouse gases. Delivering NET requires radical cost and regulatory innovation to impact on climate mitigation. Present NET exemplars are few, are at small-scale and not deployable within a decade, with the exception of rock weathering, or direct injection of CO2 into selected ocean water masses. To keep warming less than 2°C, bioenergy with CCS (BECCS) has been modelled but does not yet exist at industrial scale. CCS already exists in many forms and at low cost. However, CCS has no political drivers to enforce its deployment. We make a new analysis of all global CCS projects and model the build rate out to 2050, deducing this is 100 times too slow. Our projection to 2050 captures just 700 Mt CO2 yr-1, not the minimum 6000 Mt CO2 yr-1 required to meet the 2°C target. Hence new policies are needed to incentivize commercial CCS. A first urgent action for all countries is to commercially assess their CO2 storage. A second simple action is to assign a Certificate of CO2 Storage onto producers of fossil carbon, mandating a progressively increasing proportion of CO2 to be stored. No CCS means no 2°C.This article is part of the theme issue 'The Paris Agreement: understanding the physical and social challenges for a warming world of 1.5°C above pre-industrial levels'.

Inherent Tracers for Carbon Capture and Storage in Sedimentary Formations: Composition and Applications.

Inherent tracers-the "natural" isotopic and trace gas composition of captured CO2 streams-are potentially powerful tracers for use in CCS technology. This review outlines for the first time the expected carbon isotope and noble gas compositions of captured CO2 streams from a range of feedstocks, CO2-generating processes, and carbon capture techniques. The C-isotope composition of captured CO2 will be most strongly controlled by the feedstock, but significant isotope fractionation is possible during capture; noble gas concentrations will be controlled by the capture technique employed. Comparison with likely baseline data suggests that CO2 generated from fossil fuel feedstocks will often have δ(13)C distinguishable from storage reservoir CO2. Noble gases in amine-captured CO2 streams are likely to be low concentration, with isotopic ratios dependent on the feedstock, but CO2 captured from oxyfuel plants may be strongly enriched in Kr and Xe which are potentially valuable subsurface tracers. CO2 streams derived from fossil fuels will have noble gas isotope ratios reflecting a radiogenic component that will be difficult to distinguish in the storage reservoir, but inheritance of radiogenic components will provide an easily recognizable signature in the case of any unplanned migration into shallow aquifers or to the surface.

Estimating geological CO2 storage security to deliver on climate mitigation.

Carbon capture and storage (CCS) can help nations meet their Paris CO2 reduction commitments cost-effectively. However, lack of confidence in geologic CO2 storage security remains a barrier to CCS implementation. Here we present a numerical program that calculates CO2 storage security and leakage to the atmosphere over 10,000 years. This combines quantitative estimates of geological subsurface CO2 retention, and of surface CO2 leakage. We calculate that realistically well-regulated storage in regions with moderate well densities has a 50% probability that leakage remains below 0.0008% per year, with over 98% of the injected CO2 retained in the subsurface over 10,000 years. An unrealistic scenario, where CO2 storage is inadequately regulated, estimates that more than 78% will be retained over 10,000 years. Our modelling results suggest that geological storage of CO2 can be a secure climate change mitigation option, but we note that long-term behaviour of CO2 in the subsurface remains a key uncertainty.