Volume 8 Issue 12, December 2015

Multi-actor integrated assessment models based on well-being concepts beyond GDP could support policymakers by highlighting the interrelation of climate change mitigation and other important societal problems.

Delivery of palatable 2 °C mitigation scenarios depends on speculative negative emissions or changing the past. Scientists must make their assumptions transparent and defensible, however politically uncomfortable the conclusions.

Plate tectonics is the surface expression of mantle convection. Seismic observations at the Cascadia subduction zone show that coupling between tectonic plate motion and mantle flow may depend on the size of the plate.

Compared to Earth, the Moon is depleted in volatile species like water, sodium and potassium. Simulations suggest that much of the Moon formed from hot, volatile-poor melt in a disk of debris after initially amassing cooler, volatile-rich melt.

The last glacial period and deglaciation were marked by abrupt, millennial-scale climate changes. Changes in the North Atlantic meridional overturning circulation were important contributors to rapid climate variability, but did not act alone.

Low soil fertility can limit crop productivity, which in turn constrains the ability of poor households to invest in improving soils. This self-reinforcing feedback can trap households in chronic poverty for years or even generations.

The moon Phobos will eventually either disintegrate to form a ring or crash into Mars. Observational constraints and geotechnical considerations suggest that Phobos will partially break apart into a ring, with stronger fragments impacting Mars.

The Moon may have accreted from a disk of debris after a giant impact. Simulations suggest that part of the Moon derives from volatile-poor melt in the hot inner disk, with most of the volatile elements condensing later and accreting to Earth.

ENSO-driven rainfall patterns are set to change as the climate warms. A moisture budget decomposition of simulations from 18 climate models reveals the mechanisms driving the shift in rainfall variability from western to central Pacific.

Ice shelves modulate Antarctica’s contributions to sea-level rise. Regional-climate-model simulations and observations suggest historical ice melt intensification before collapse of Antarctic peninsula shelves, and project future melt evolution.

Lakes are a large source of CO₂. An analysis of chemical and physical data from 5,118 boreal lakes reveals that a majority emit CO₂ originating primarily from terrestrial sources rather than CO₂ produced within the lakes.

Oxygen minimum zones exert important controls over ocean biogeochemistry. Lagrangian modelling demonstrates that the mean positions of mesoscale eddies delimit the boundaries of the Peruvian oxygen minimum zone.

Microbe-mediated reactions remove nitrogen from river water as it flows through sediments. Simulations of the Mississippi River network suggest that denitrification due to flow through small-scale river bedforms exceeds that along channel banks.

The last deglaciation was interrupted by a cool period known as the Younger Dryas. Numerical simulations suggest that the cold interval was the result of a combination of changes in ocean and atmospheric circulation and reduced radiative forcing.

The last glacial period was characterized by a series of abrupt climate changes. An analysis of bottom water chemistry in the South Atlantic suggests that the southern extent of North Atlantic Deep Water was reduced during abrupt coolings.

Slip during subduction zone earthquakes is often assumed to occur on a single fault. Analysis of a 2011 Chilean earthquake shows that the event was composed of two quakes, with megathrust rupture triggering slip in the overriding plate.

Subduction carries water into the Earth where it can influence seismicity. Analysis of the structure of the Alaskan subduction zone suggests fluid delivery is influenced by faults in the oceanic plate that formed at the mid-ocean ridge.

Shallow mantle flow could be induced by the motions of overriding tectonic plates or by deeper mantle convection. Analysis of mantle flow patterns in the Pacific Northwest shows that flow aligns with the motions of the largest oceanic plates.

The width of the tropical belt affects the subtropical dry zones and has expanded since 1980. Analyses of observations and climate–chemistry model simulations suggest that the northern tropical edge retracted between 1945 and 1980.

Global mean temperatures during the Pliocene epoch were warmer than at present, with a shallow meridional temperature gradient. Numerical simulations suggest that since the Pliocene, the meridional and zonal temperature gradients have varied in tandem.