Volume 7 Issue 5, May 2014

Livestock production accounts for a significant fraction of global anthropogenic greenhouse gas emissions. Progress in mitigating the adverse environmental impacts of this industry can be improved by shifting research emphases and fostering communication between researchers and ranchers.

Large tracts of agricultural land are being bought up by external investors. Turning the land into a commodity can have detrimental effects, for generations to come, on the local communities that sell or lease the land.

Biochar has been heralded as a solution to a number of agricultural and environmental ills. To get the most benefit from its application, environmental and social circumstances should both be considered.

A dense early atmosphere has been invoked to explain the strong greenhouse effect inferred for early Mars. Yet an analysis of the smallest impact craters suggests that the atmospheric pressure on Mars 3.6 billion years ago was surprisingly low.

Ocean island lavas have complex geochemical signatures. Numerical simulations suggest that these signatures may reflect the entrainment and transport to Earth's surface of both primordial material and recycled oceanic crust by deeply rooted mantle plumes.

Record-breaking heatwaves in 2003 and 2010 surprised both the public and experts. Observations provide new insights into how temperatures escalated to unprecedented values through the interaction of boundary-layer dynamics and land surface drying.

Carbon loss from subducting slabs is thought to be insufficient to balance carbon dioxide emissions at arc volcanoes. Analyses of ancient subducted rocks in Greece suggest that fluid dissolution of slab carbonate can help solve this carbon-cycle conundrum.

The martian atmosphere has progressively thinned, allowing increasingly smaller meteorites to survive unscathed and impact the surface. The distribution of small craters in ancient river deposits on Mars suggests an atmospheric pressure less than that needed to warm the martian surface above freezing 3.5 billion years ago, when rivers presumably flowed.

The downward transport of stratospheric air can deliver significant quantities of ozone to the upper troposphere. An analysis of satellite data suggests that year-to-year variations in stratospheric circulation can account for around half of the interannual variability in tropospheric ozone levels in the northern mid-latitudes.

Extreme heatwave events are expected to become increasingly common as a consequence of climate change. Analyses of the 2003 and 2010 mega-heatwaves in Europe suggest that atmospheric boundary-layer dynamics and feedbacks with the drying land surface lead to the build-up of heat in the atmosphere and extremely hot temperatures.

Dams have starved the lower Mississippi River of sediment over recent decades, suggesting that the drowning of the delta is inevitable. Analysis of the rivers suspended sediment load and morphodynamic modelling suggest that the amount of sand essential for land building has not significantly decreased since dam construction, with sand remaining available for several centuries.

The balance between carbonate subduction into the deep Earth and CO₂ release through degassing at volcanoes is critical for the carbon cycle. Geochemical analyses of an exhumed subduction zone complex in Greece show that fluid-mediated reactions could liberate significant amounts of carbon from the subducting slab for later release at arc volcanoes.

The Tibetan Plateau is expanding eastwards, but the modes of deformation are poorly understood. High-resolution seismic images from the region identify localized zones of weak crustal rocks as well as deep faults, implying that deformation occurs through a combination of crustal flow and movement of rigid blocks of crust.

Lavas erupted at ocean island hotspots have complex geochemical signatures. Numerical simulations suggest that this complexity may result from the mixing of subducted oceanic crust with reservoirs of more primitive material in the deep mantle, with the resulting mixture entrained into rising mantle plumes.

At oceanic spreading centres, it is unclear whether plate motions drag the underlying mantle, or mantle flow pulls the overlying plates. Seismic imaging of a former speading centre in the Pacific Plate reveals strong seismic anisotropy that was generated by mantle flowing at speeds greater than plate motions, implying that mantle flow pulled this part of the plate.

During the expansion of the Antarctic ice sheet about 14 million years ago, sea surface temperatures in the Southern Ocean rose. Climate model simulations suggest that this short-lived warming was related to changes in ocean–atmosphere circulation induced by the growth of the ice sheet.

Globally increased temperatures and a perturbation of the carbon cycle and biosphere characterized the Palaeocene–Eocene Thermal Maximum about 55.9 million years ago, but its effect on ocean productivity is controversial. Records of marine barite accumulation rates suggest that carbon sequestration during the event could have been enhanced by an efficient biological pump.

If food production is to keep pace with the demands of an ever-expanding global population, agricultural systems must be modified to cope with the rising temperatures and increased prevalence of droughts, floods and other extreme weather events that are projected to ensue. A series of opinion pieces in this issue explore some of the ways in which productivity can be improved and food security safeguarded, be it through the direct involvement of those that work on the land, partnerships between remote investors and local land owners, or treatments tailored to the agricultural system in hand.