Economic costs of wind erosion in the United States
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Onshore intensification of subtropical western boundary currents in a warming climate
Subtropical western boundary currents (WBCs) refer to swift narrow oceanic currents that flow along the western edges of global subtropical ocean basins. Earlier studies indicated that the WBCs are extending poleward under a warming climate. However, owing to limited observations and coarse resolution of climate models, how greenhouse warming may affect the zonal structure of the WBCs remains unknown. Here, using seven high-resolution climate models, we find an onshore intensification of the WBCs in a warming climate. The multimodel ensemble mean of onshore acceleration ranges from 0.10 ± 0.08 to 0.51 ± 0.24 cm s−1 per decade over 1950–2050. Enhanced oceanic stratification associated with fast surface warming induces an uplift of the WBCs, leading to the projected change. The onshore intensification could induce anomalous warming that exacerbates coastal marine heatwaves, reduces ability of the coastal oceans to absorb anthropogenic carbon dioxide and destabilizes methane hydrate stored below the sea floor of shelf regions.
Seasonal regimes of warm Circumpolar Deep Water intrusion toward Antarctic ice shelves
Basal melting of Antarctic ice shelves is primarily driven by heat delivery from warm Circumpolar Deep Water. Here we classify near-shelf water masses in an eddy-resolving numerical model of the Southern Ocean to develop a unified view of warm water intrusion onto the Antarctic continental shelf. We identify four regimes on seasonal timescales. In regime 1 (East Antarctica), heat intrusions are driven by easterly winds via Ekman dynamics. In regime 2 (West Antarctica), intrusion is primarily determined by the strength of a shelf-break undercurrent. In regime 3, the warm water cycle on the shelf is in antiphase with dense shelf water production (Adélie Coast). Finally, in regime 4 (Weddell and Ross seas), shelf-ward warm water inflow occurs along the western edge of canyons during periods of dense shelf water outflow. Our results advocate for a reformulation of the traditional annual-mean regime classification of the Antarctic continental shelf.
Diversity of biomass usage pathways to achieve emissions targets in the European energy system
Biomass is a versatile renewable energy source with applications across the energy system, but it is a limited resource and its usage needs prioritization. We use a sector-coupled European energy system model to explore near-optimal solutions for achieving emissions targets. We find that provision of biogenic carbon has higher value than bioenergy provision. Energy system costs increase by 20% if biomass is excluded at a net-negative (−110%) emissions target and by 14% at a net-zero target. Dispatchable bioelectricity covering ~1% of total electricity generation strengthens supply reliability. Otherwise, it is not crucial in which sector biomass is used, if combined with carbon capture to enable negative emissions and feedstock for e-fuel production. A shortage of renewable electricity or hydrogen supply primarily increases the value of using biomass for fuel production. Results are sensitive to upstream emissions of biomass, carbon sequestration capacity and costs of direct air capture.
Poleward displacement of the Southern Hemisphere Westerlies in response to Early Holocene warming
Recent intensification of the Southern Hemisphere Westerlies has resulted in important changes to ocean circulation, Antarctic ice shelf stability and precipitation regimes in the continents abutting the Southern Ocean. Efforts to resolve the natural behaviour of the Westerlies over sub-millennial to millennial-timescales are critical to anticipating future changes with continued 21st Century warming. Here we present an ~11,000 year diatom-inferred sea salt aerosol and multiproxy geochemical record preserved in lake sediments from Cape Horn (56°S) which documents warm conditions and stronger-than-present Westerlies in the Early Holocene (10 000–7500 calibrated years before present) at this site. Combined with other regional records, we demonstrate that the Westerlies were poleward of their current position during the Early Holocene. This poleward migration of the Southern Hemisphere Westerlies in response to peak Holocene warmth provides an analogue for future warming and greater impacts on the southern high latitudes and global climate in the coming decades.
The growth of super-large pre-planetary pebbles to an impact erosion limit
The early evolution of dust in protoplanetary disks is dominated by sticking collisions. However, this initial phase of particle growth faces constraints, notably from destructive encounters. To find the maximum particle size achievable, we studied collisional processes during a prolonged microgravity experiment aboard a suborbital flight. Specifically, we describe an impact erosion limit. We observed individual basalt beads, each measuring 0.5 mm in diameter, colliding with and either eroding or adhering to a cluster several centimetres in size. This cluster, formed from tribocharged particles, simulates an electrostatic growth phase that surpasses the classical bouncing barrier. We found a threshold velocity of about 0.5 m s−1, which separates additive and erosive impacts of individual beads. Numerical simulations of grains impacting clusters, for both low and high charge constituents, corroborate the experimental findings of surface erosion within the observed velocity range. This specific velocity threshold supports the potential formation of pebbles several centimetres in size within protoplanetary disks. Such dimensions place these pebbles well into a regime in which hydrodynamic interactions might facilitate the formation of planetesimals.
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