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Gullies on Mars have been linked to possible flowing water, but are most active when seasonal CO2 ice is defrosting. Numerical modelling suggests that CO2 ice sublimation can induce debris flows consistent with observations of martian gullies.
El Niño events tend to suppress Atlantic hurricane activity. Simulations with high-resolution climate models show that the efficiency of this suppression mechanism varies with the flavour of the El Niño event.
The frequency and amplitude of the El Niño/Southern Oscillation varied during the Holocene. A comparison of proxy records and model simulations suggests that any link between orbital forcing and this variability is either complex or non-existent.
Microbial reduction of arsenic-bearing iron oxides releases arsenic into groundwater in Asia. Laboratory and field studies in the Mekong Delta reveal that arsenic release is limited to near-surface sediments of permanently saturated wetlands.
Flood basalt eruptions have been linked to extinction events. Numerical simulations suggest that the environmental effects of sulphur emissions from these volcanoes would be limited unless the eruptions were frequent and sustained.
Global mean temperatures during the Pliocene epoch were warmer than at present, with a shallow meridional temperature gradient. Numerical simulations suggest that since the Pliocene, the meridional and zonal temperature gradients have varied in tandem.
Groundwater recharged less than 50 years ago is vulnerable to contamination and land-use changes. Data and simulations suggest that up to 6% of continental groundwater is modern—forming the largest component of the active hydrologic cycle.
The observed increases in hurricane losses are often thought to result solely from societal change. A regression-based analysis of US economic losses reveals an upward trend between 1900 and 2005 that is not explained by increasing vulnerability.
The width of the tropical belt affects the subtropical dry zones and has expanded since 1980. Analyses of observations and climate–chemistry model simulations suggest that the northern tropical edge retracted between 1945 and 1980.
Pyrite formation has been considered a key iron sink in organic-rich marine sediments. Analyses of sediments from the Ivory Coast–Ghana Marginal Ridge demonstrate that iron can be buried at greater rates during green-clay formation.
The dynamic components of coastal water level can add metres to water levels during extreme events. A data synthesis reveals that Pacific regional wave and water level fluctuations are closely related to the El Niño/Southern Oscillation.
It is unclear how Archaean crust formed. Analysis of seismic data from Western Australia suggests that ancient crust first formed in mantle plume-like settings and later in subduction zones, possibly in response to secular cooling of the mantle.
How plate tectonic subduction is initiated is unclear. Analysis of sediments and rock cores taken from the Izu–Bonin–Mariana subduction zone trench suggests subduction started spontaneously in this region around 50 million years ago.
Long-term changes of the mountain glaciers in the Tien Shan, Central Asia, are not well constrained. Remote sensing data and glaciological models reveal a 27% decline of glacier mass from 1961 to 2012, linked to increased summer melting.
Ammonium levels in Greenland ice cores track changes in soil emissions and wildfires, primarily in North America. Ice-core ammonium records show abrupt increases in wildfire activity during brief warmings in the last glacial period.
Changes in Arctic sea ice volume are difficult to quantify. Five years of satellite data reveal a reduction in autumn sea ice volume in 2010–2012, but a sharp increase in 2013 and 2014, suggesting that ice volume can recover quickly.
Inland waters are important sources of greenhouse gases. Measurements over eight years suggest that African inland waters are a substantial source of greenhouse gases, equivalent to a quarter of the global land and ocean carbon sink.
The frequency of extreme rainfall events over Greenland is predicted to increase as the climate warms. Observations from western Greenland suggest that intense late-summer rainfall in 2011 led to widespread ice-flow acceleration and runoff.
The climate-model mean response of the summertime mid-latitude circulation to global warming is weak. Model experiments reveal that a tug of war between the influences of radiative forcing and surface warming is the reason.
The controls on plant functional diversity are unclear. Analysis of spectral data from the tree canopy in the Amazonian lowlands implies that plant functional traits are influenced by nutrient supply, which in turn varies with topography.