Volume 9 Issue 4, April 2016

The need to mitigate climate change opens up a key role for cities. Bristol's year as a Green Capital led to great strides forward, but it also revealed that a creative and determined partnership across cultural divides will be necessary.

The Antarctic ice sheet is fringed by ice shelves. Remote imagery identifies extensive basal channels in these shelves that grow and deepen on decadal timescales.

A rapid warming event 55.8 million years ago was caused by extensive carbon emissions. The rate of change of carbon and oxygen isotopes in marine shelf sediments suggests that carbon emission rates were much slower than anthropogenic emissions.

Large earthquakes cause other quakes near and far. Analyses of quakes in Pakistan and Chile suggest that such triggering can occur almost instantaneously, making triggered events hard to detect, and potentially enhancing the associated hazards.

Human activity alters the atmospheric composition, which leads to global warming. Model simulations suggest that reductions in emission of sulfur dioxide from Europe since the 1970s could have unveiled rapid Arctic greenhouse gas warming.

Mercury appears darker globally than expected. Remote sensing evidence from the MESSENGER spacecraft indicates that the planet’s darkening agent is carbon and suggests that it originates from an ancient graphite-rich crust.

The reasons for amplified warming in the Arctic are not clear. Simulations with an Earth system model suggest that the decline in European aerosol emissions since 1980 explains a substantial fraction of the warming.

Atmospheric sulfate levels are thought to determine the pH of small aerosol particles. Thermodynamic analysis of field aerosol data reveals that fine particles remain acidic in the southeastern United States despite large sulfate reductions.

Earth’s climate sensitivity has been debated. An econometric analysis of observations shows that aerosol cooling has masked about one-third of greenhouse gas warming and yields a transient climate sensitivity of 2 ± 0.8 °C.

The Antarctic Ice Sheet is buttressed by floating ice shelves. Remote sensing data show extensive basal channels, particularly in West Antarctica, which grow quickly in response to warm water intrusion.

Microbes can mineralize metals such as gold. Observations of platinum-group mineral grains and incubation experiments reveal that bacteria can also transform these metals, which could affect their mobility in surface environments.

How gold ore deposits form in the absence of a magmatic source for gold is unclear. Analysis of hydrothermal fluids from the Reykjanes geothermal field reveals that gold can become trapped as a colloidal suspension and accumulate over time.

Large earthquakes can rupture several faults. Analysis of seismic data from the 2010 El Mayor–Cucapah earthquake in California suggests that multiple faults were pinned to a keystone fault whose rupture triggered cascading slip.

One volcanic eruption can trigger another. Global analysis of coupled eruptions suggests that the extent of magma mush, stress changes, dyke intrusions and earthquakes can couple volcanic eruptions over increasing distances.

The polygonal patterns in permafrost regions are caused by the formation of ice wedges. Observations of polygon evolution reveal that rapid ice-wedge melting has occurred across the Arctic since 1950, altering tundra hydrology.

The amount of carbon dioxide in the atmosphere declined as the Earth entered the last glacial period. Estimates of deep carbonate ion concentrations suggest that a substantial amount of carbon was sequestered in the deep Atlantic Ocean.

Carbon release rates during the Palaeocene–Eocene Thermal Maximum are difficult to constrain. Comparing relative rates of carbon cycle and climate change at the event’s onset suggests emissions were much slower than anthropogenic emissions.

Assessments of earthquake risk often assume rupture of a single fault. Analysis of a 1997 Pakistan earthquake reveals that not one but two separate ruptures caused the shaking, implying that cascading events should be factored into forecasts.