Volume 4 Issue 7, July 2011

A cultural divide separates science from the media. To bridge the gulf, Nature Geoscience presents a science writer's perspective on the Earth sciences in a new monthly column.

State-of-the-art climate models are largely untested against actual occurrences of abrupt change. It is a huge leap of faith to assume that simulations of the coming century with these models will provide reliable warning of sudden, catastrophic events.

Accurate prediction of Earth's future warming hinges on our understanding of climate sensitivity. Palaeoclimatology will help solve the problem if the feedbacks included in palaeoclimate sensitivity are properly identified and reconstructions of past atmospheric CO₂ can be improved.

Reconstructions of atmospheric carbon dioxide concentrations over the past 65 million years are heading towards consensus. It is time for systematic testing of the proxies, against measurements and against each other.

Large earthquakes can build mountains, but they can also trigger landslides that wear landscapes away. An analysis from the 2008 Wenchuan earthquake shows that landslides destroyed more topography than was created by uplift.

Oxygen isotope variations in Chinese cave deposits have been interpreted as proxies for the East Asian summer monsoon. Numerical simulations suggest the deposits may instead record remote climate changes over India and the Indian Ocean.

The relationship between soil moisture and rainfall has proved tricky to pin down. An analysis of close to 4,000 Sahelian storms suggests that certain soil-moisture patterns enhance the likelihood of rainfall.

The southern San Andreas fault is due for a large earthquake. Seismic images of sediments deposited in an ancient lake overlying the southern end of the fault indicate that episodic flooding may have triggered earthquakes in the past.

Evapotranspiration of soil moisture can affect rainfall and the development of convective storms. Satellite observations of cloud and land-surface temperatures over the Sahel suggest that convective storms are more likely to form over strong mesoscale gradients in soil moisture.

Feedbacks between soil moisture and precipitation are among the most important land–atmosphere interactions. An analysis of evaporative fluxes over North America suggests that the probability of afternoon rainfall in Mexico and the eastern United States is increased during periods of enhanced evaporation.

Photolysis of nitrous acid generates hydroxyl radicals — a key atmospheric oxidant. Measurements at a forest in Michigan suggest that sunlight-induced breakdown of nitric acid on the canopy surface serves as a significant source of nitrous acid to the overlying atmosphere.

Wetlands take up and store carbon, and release methane, through the decomposition of organic matter. Model simulations suggest that the areal extent of wetlands declines when permafrost thaws.

Shallow earthquakes lead to the uplift of mountain ranges, but also trigger landslides that remove mass. An analysis of the 2008 Wenshuan earthquake suggests that more material was removed from the orogen by widespread landslides than was added by coseismic uplift.

Sediments accumulated in a subduction trench are usually unconsolidated and impede the updip propagation of fault rupture during an earthquake. Seismic images of the southern Sumatra–Andaman trench reveal blocks of consolidated sediment that may have enabled fault rupture in 2004 to propagate up fault dip, thus further seaward, increasing the tsunami magnitude.

Variations in the volume, geochemistry and location of volcanism in Hawaii cannot be explained as the simple consequence of an underlying mantle plume. A numerical model of the Hawaiian plume suggests that small-scale convection in the mantle erodes the base of the overlying tectonic plate and may help generate the anomalous volcanism.

Hydrothermal vents along mid-ocean ridge systems host highly productive communities of microbes. Measurements along the Juan de Fuca ridge suggest that subsurface microbes consume hydrogen in low-temperature hydrothermal fluids, before discharge of these fluids at the sea floor.

Erosion in the Washington Cascades Mountains was dominated by glacier activity until the end of the Last Glacial Maximum, when fluvial incision and mass wasting became the dominant drivers. An analysis of millennial-scale rates of denudation in the range suggest erosion is sensitive both to spatial variations in precipitation and inherited topography.

Cave deposits from China are commonly used to reconstruct the intensity of the East Asian monsoon precipitation. Numerical modelling indicates that these deposits may instead reflect changes in the strength of Indian monsoon precipitation and the isotopic signature of water vapour exported from India to China.

A brief period of warming 55.9 Myr ago has been attributed to the release of massive amounts of carbon. Geochemical and model data suggest the peak rate of carbon emission during this interval was relatively slow, and significantly lower than present-day levels of carbon emissions to the atmosphere.

The southern San Andreas fault terminates in a stepover zone — several small faults that separate major fault segments — beneath the Salton Sea. Analysis of movements on the stepover zone faults indicates that periodic flooding of the palaeo-Salton Sea during the late Holocene could have triggered earthquakes on the San Andreas fault.

Understanding the amplitude of climate variability in the past, as well as the causes and mechanisms responsible for this variability is important in its own right. Yet it also helps us get a better idea of the range of possible Earth system responses to human-induced greenhouse gas emissions. In this web focus we explore the links between past climate and carbon cycle perturbations, along with the ability of state-of-the-art climate models to capture these links.