Volume 7 Issue 2, February 2014

Scientific climate information can save lives and livelihoods, yet its application is not always straightforward. Much of the available information does not describe the risk of threshold events, and misunderstandings can leave society less resilient to climate shocks.

Global mean surface temperatures have not risen much over the past 15 years, despite continuing greenhouse gas emissions. An attempt to explain the warming slow-down with Arctic data gaps is only a small step towards reconciling observed and expected warming.

Eruptions come in a range of magnitudes. Numerical simulations and laboratory experiments show that rare, giant super-eruptions and smaller, more frequent events reflect a transition in the essential driving forces for volcanism.

Runoff estimates from the Greenland ice sheet carry uncertainty because the fate of surface melt in permanently snow-covered regions is unconstrained. In situ and airborne observations reveal large-scale liquid water storage in buried layers of aged and compacted snow.

A slowing Atlantic overturning circulation during the last deglacial warming caused abrupt cooling in the Northern Hemisphere. Lake sediment records suggest that hydrological change in Europe lagged the temperature drop by almost 200 years.

Wind systems determine the transport pathways of air pollutants such as ozone. Simulations with a chemistry-climate model suggest that decadal shifts in atmospheric circulation have helped shape season-specific trends in surface ozone levels in Hawaii since the 1990s.

Chlorine radicals function as a strong atmospheric oxidant, particularly in polar regions, where levels of hydroxyl radicals are low. Measurements in the Arctic reveal high levels of molecular chlorine during the day, consistent with a photochemical source.

Surface melt water from the Greenland ice sheet can become trapped in firn, delaying its journey to the sea. Radar and ice-core observations provide direct evidence of a perennial aquifer in the firn layer in southern Greenland that represents a potentially significant contribution to the Greenland mass budget.

The dynamics of dune evolution under bimodal wind regimes are poorly understood owing to a lack of long-term wind records and the limitations of most experimental set-ups. A 4-year landscape-scale experiment in the Tengger Desert, Mongolia, demonstrates that the orientation of oblique dune crests is controlled by the wind regime.

Climate variations over the past 1,000 years correspond to solar fluctuations, but the magnitude of the solar variability is unclear. An analysis of numerical simulations and climate reconstructions suggests that the amplitude of solar forcing was small over this interval, with the main climate forcing derived from volcanic eruptions and greenhouse gas concentrations.

During the Younger Dryas cold event about 12,800 years ago, environmental change in western Europe seems to occur 170 years after cooling over Greenland. Lake sediment analyses confirm this delay, and suggest European hydrological and vegetation change occurred only after the build-up of sea ice in the North Atlantic pushed the westerly wind system south.

Relatively little is known about the dynamics of the Antarctic Circumpolar Current during the last glacial period. Estimates of current speeds over the past 20,000 years based on sediment grain size suggest that average flow speeds during the last glacial were comparable to modern speeds, but not in the areas with overlying winter sea ice.

Part of the subduction zone plate interface beneath Costa Rica was previously locked, which allowed strain to accumulate. Analyses using GPS and geomorphic data show that almost the entire locked region ruptured during a megathrust quake in 2012, implying that plate-interface mapping towards the end of the earthquake cycle can aid seismic hazard assessments.

Supervolcano eruptions dwarf all historical eruptions, but their trigger mechanisms are unclear. Experimental measurements of magma density at high pressures and temperatures show that the buoyancy of magma alone can impose sufficient pressure at the roof of a supervolcano magma chamber to induce an eruption.

The global frequency of volcanic eruptions is inversely proportional to the volume of magma erupted in a single event. Numerical modelling of magma reservoirs evolving in Earth’s crust shows that frequent, small eruptions are triggered by injections of magma into the reservoir, but rare, giant supervolcano eruptions are triggered by magma buoyancy.

The dynamics of Earth’s mantle are difficult to constrain. Analysis of GOCE satellite gravity data can be used to identify gravity anomalies to mid-mantle depths and hence to identify regions of tectonic-plate subduction and plume upwelling in the mantle.

Tropospheric ozone is a potent greenhouse gas, biological irritant and significant source of highly reactive hydroxyl radicals. Simulations with a chemistry climate model suggest that shifts in atmospheric circulation can account for the seasonally dependent trends in tropospheric ozone levels observed at Mauna Loa, Hawaii, over the past three decades.

Several periods of massive iceberg discharge into the North Atlantic and widespread cooling marked the last glacial period. Reconstructions of northward flow along the Florida margin suggest that not all cold events were associated with a change in the strength of the Atlantic meridional overturning circulation.

Upwelling mantle plumes are thought to be sheared by the motions of the overlying tectonic plates. Seismic imaging of a hotspot beneath the Galápagos Islands, however, identifies a plume that is not deflected in the direction of plate motion and whose characteristics are instead controlled by multistage melting processes.