Volume 7 Issue 3, March 2014

Climate models projected stronger warming over the past 15 years than has been seen in observations. Conspiring factors of errors in volcanic and solar inputs, representations of aerosols, and El Niño evolution, may explain most of the discrepancy.

Decadal climate variability has long received limited attention. With the slow-down in surface warming since the late 1990s, the decadal scale has rightly become a focus of attention: for assessing climate change and its impacts, it is of critical importance.

Little is known about the presence of high-latitude sea ice before 2.6 million years ago. A reanalysis of marine sediments from the Arctic Ocean indicates an intermittent presence of perennial sea ice as early as 44 million years ago.

Despite reports of no trends in snow- and rainfall, rivers in the northwest USA have run lower and lower in recent decades. A closer look at high- and low-altitude precipitation suggests that observational networks have missed a decline in mountain rain and snow that can explain the discrepancy.

Volcanic plumes can be hazardous to aircraft. A correlation between plume height and ground deformation during an eruption of Grímsvötn Volcano, Iceland, allows us to peer into the properties of the magma chamber and may improve eruption forecasts.

The age of the oldest Jack Hills zircons — Earth's oldest minerals — is contentious. Atomic-scale mapping of the distribution of radiogenic isotopes within a Jack Hills zircon confirms that the oldest known continental crust formed just after the Earth–Moon system.

The end-Permian extinction decimated marine life on an unprecedented scale. However, an analysis of the lifestyles of the surviving genera shows that very little functional diversity was lost at the sea floor.

Feedbacks between the terrestrial carbon cycle and climate change could affect many ecosystem functions and services. A synthesis of global air temperature data reveals non-uniform rates of climate warming on diurnal and seasonal timescales, and heterogeneous impacts on ecosystem carbon cycling.

Changes in climate are amplified in the Arctic region. An analysis of the CMIP5 state-of-the-art climate models reveals that temperature feedbacks are the dominant factor in this amplification, whereas the change in reflectivity of the Earth’s surface as sea ice and snow melt makes only a secondary contribution.

Global mean surface and tropospheric temperatures have shown slower warming since 1998 than found in climate model simulations. A detailed analysis of observations and climate model simulations suggests that the observed influence of volcanic eruptions on tropospheric temperature has been significant, and that the discrepancy between climate simulations and observations is reduced by up to 15% when twenty-first century volcanic eruptions are accounted for in the models.

The flux of methane from the sea bed to the overlying water column is mitigated by the sulphate-dependent anaerobic oxidation of methane by marine microbes. Laboratory experiments point to the equilibration of stable carbon isotopes during the anaerobic oxidation of methane under sulphate-limited conditions.

Humic substances make up a significant fraction of the natural organic matter in terrestrial and aquatic environments. Laboratory experiments suggest that humic substances serve as fully regenerable electron acceptors in recurrently anoxic environments such as peatlands.

Carbon is removed from the Earth’s surface through the formation and burial of carbon-bearing rocks and minerals. An analysis of pore water profiles collected from marine sediments around the globe suggests that the precipitation of authigenic calcium carbonate accounts for around 10% of the carbonate that accumulates in marine sediments globally.

During the Last Glacial Maximum, tropical glacier snowlines were lower than expected, based on estimates of tropical sea surface temperatures. Sea surface temperature reconstructions suggest the Indo-Pacific warm pool was cooler than previously thought; these temperatures and convective mixing processes can explain snowline altitude in this region.

Arctic sea ice is a key component of the modern climate system. Marine sediment analyses suggest that perennial sea ice in the Arctic Ocean first formed—transiently—about 44 million years ago.

The 2011 eruption of a 20-km-high volcanic plume from Grímsvötn Volcano, Iceland, led to the closure of northern European airspace. Geodetic measurements from the volcano reveal a correlation between plume height, surface deformation and magma-chamber pressure, with a delay of an hour, implying that volcanic-plume behaviour can be predicted before eruption onset.

The oldest minerals on Earth are thought to have formed in the Hadean eon, but the reliability of the dates has been questioned. Atom-probe tomography of an ancient zircon confirms that the mineral formed about 4.4 billion years ago, implying that any mixing event of the silicate Earth occurred before that time.

Hydrous magnesium-rich silicates play an important role in transporting water into the deep mantle when oceanic plates subduct as slabs, but were thought to dissociate at pressures of 44 GPa. In situ X-ray measurements in conjunction with a multi-anvil apparatus show that hydrous phases of magnesium-rich silicate are stable under lower mantle conditions up to 50 GPa, and may transport water to deeper layers of the mantle.

Breaking waves on the ocean surface generate air bubbles that yield sea spray aerosols when released to the atmosphere. Measurements of sea spray aerosols in the North Atlantic Ocean and the coastal waters of California suggest that the surface water organic carbon reservoir is responsible for the organic carbon enrichment of freshly emitted sea spray aerosol.

At least two-thirds of marine genera died out during the end-Permian mass extinction about 252 million years ago. An analysis of extinct and surviving taxa shows no substantial loss in global functional diversity, although there were significant losses in some settings such as tropical reefs.

The age of the Grand Canyon is fervently debated. Thermochronological reconstructions of canyon incision show that although parts of the canyon were carved more than 50 million years ago, two key segments formed less than 6 million years ago, implying that the canyon is a young feature.

From the industrial revolution onwards, greenhouse gas emissions resulting from human activities such as the burning of fossil fuel and changes in land use have caused the planet to warm. However, since 1998 — a year of record warmth — the rate of warming has been lower than in the late twentieth century. In this joint web focus, Nature Climate ChangeandNature Geosciencepresent original research and opinion pieces that discuss the causes of the slowdown in surface warming and examine how the science has been communicated by researchers and the media.