Volume 9 Issue 1, January 2016

In the absence of an enforceable set of commitments to reduce greenhouse gas emissions, concerned citizens may want to supplement international agreements on climate change. We suggest that litigation could have an important role to play.

Some climate change impacts rise fast with little warming, and then taper off. To avoid diminishing incentives to reduce emissions and inadvertently slipping into a lower-welfare world, mitigation policy needs to be ambitious early on.

The structure of atmospheric aerosol particles affects their reactivity and growth rates. Measurements of aerosol properties over the Amazon rainforest indicate that organic particles above tropical rainforests are simple liquid drops.

Clear evidence for subduction-induced metamorphism, and thus the operation of plate tectonics on the ancient Earth has been lacking. Theoretical calculations indicate that we may have been looking for something that cannot exist.

Martian gullies have been seen as evidence for past surface water runoff. However, numerical modelling now suggests that accumulation and sublimation of carbon dioxide ice, rather than overland flow of liquid water, may be driving modern gully formation.

Many governments agreed to limit global mean temperature change to below 2 °C, yet this level has not been assessed scientifically. A synthesis of the literature suggests that temperature is the best available target quantity, but a safe level is uncertain.

Jupiter’s banded cloud layer contains enigmatic jets and vortices. Numerical simulations show that both features originate at depth in giant planet atmospheres, with vortices developing in areas of upwelling to shallow layers.

Extreme daily precipitation is thought to increase with warming at a rate of 6.5% per K. High-resolution simulations for the southern UK show this scaling for present conditions, but above 22 °C this scaling fails owing to changes in dynamics.

Closure of the Earth’s energy budget relies on strong aerosol cooling since 1998, if the same feedbacks apply for anthropogenic and natural variability. An analysis of climate model simulations suggests that these feedbacks are instead distinct.

The physical state of atmospheric particulate matter affects its growth and reactivity, which can affect climate. Measurements of particle rebound reveal that particulate matter over the Amazon forest is usually liquid during wet and dry seasons.

The sediment load of China’s Yellow River has been declining. Analysis of 60 years of runoff and sediment load data attributes this decline to river engineering, with an increasing role of post-1990s land use changes on the Loess Plateau.

In active mountain belts, erosion is driven by bedrock landsliding. River water chemistry in New Zealand’s Southern Alps suggests that stochastic mass wasting processes also enhance chemical weathering in such environments.

During the last deglaciation, the Indian summer monsoon failed during periods of cooling in the North Atlantic. Sediment records suggest that the concomitant cooling of the surface of the Arabian Sea contributed to the monsoon weakening.

The last deglaciation was interrupted by the Antarctic Cold Reversal. Proxy records and climate modelling suggest that a redistribution of oceanic and atmospheric heat caused changes in temperature and hydrology across the Southern Hemisphere.

Subducting oceanic plates are often considered as cold, rigid slabs. Analysis of seismic anisotropy in the subducted Nazca Plate beneath Peru suggests that the plate has deformed internally during subduction.

An absence in the ancient geological record of blueschist metamorphic rocks has been taken as evidence against early subduction. Thermodynamic calculations now suggest that blueschist rocks could not have formed on a younger, hotter Earth.

Gullies on Mars have been linked to possible flowing water, but are most active when seasonal CO₂ ice is defrosting. Numerical modelling suggests that CO₂ ice sublimation can induce debris flows consistent with observations of martian gullies.

Microbial reduction of arsenic-bearing iron oxides releases arsenic into groundwater in Asia. Laboratory and field studies in the Mekong Delta reveal that arsenic release is limited to near-surface sediments of permanently saturated wetlands.

Flood basalt eruptions have been linked to extinction events. Numerical simulations suggest that the environmental effects of sulphur emissions from these volcanoes would be limited unless the eruptions were frequent and sustained.