Commentary

A multitude of organisms makes soils the fertile factories of food and fibre production, decomposition and nutrient cycling that they are. But tying changes in soil biodiversity to shifts in ecosystem function is a daunting task.

Twitter messages offer first-hand accounts of earthquakes within minutes. Analyses of their content and geographic distribution can be a useful supplement to instrument-based estimates of quake location and magnitude.

Nearly an eighth of the population in Bangladesh relies on arsenic-contaminated drinking water. Arsenic-removal filters could help to reduce exposure, but their price is high for the poor and their maintenance is cumbersome.

The fact that cumulative carbon dioxide emissions are more important than annual emission rates calls for a fresh approach to climate change mitigation. One option would be a mandatory link between carbon sequestration and fossil fuel extraction.

Storage of the carbon dioxide that is produced by burning fossil fuels is one way to avoid the damaging consequences of climate change. A range of observations suggests that geological carbon storage is much less risky than unabated carbon emissions to the atmosphere.

The conversion of coal into liquid fuel is one of the dirtiest ways to produce transportation fuel. But if carbon is captured and stored, and some biomass is added, it could become the cleanest way to power jets, trucks and trains.

The path towards mitigating global warming is going to be tortuous. Capturing carbon dioxide and pumping it directly into the deep ocean to avoid atmospheric build-up is an option that has been dismissed prematurely.

Deforestation is the second largest anthropogenic source of carbon dioxide to the atmosphere, after fossil fuel combustion. Following a budget reanalysis, the contribution from deforestation is revised downwards, but tropical peatlands emerge as a notable carbon dioxide source.

Charles Darwin became the founder and mythic hero of modern evolutionary biology with the publication of his work On the Origin of Species 150 years ago. The book bears the signature of a geological thinker who had turned to a faster-moving discipline.

The terrestrial biosphere is assumed to take up most of the carbon on land. However, it is becoming clear that inland waters process large amounts of organic carbon and must be considered in strategies to mitigate climate change.

Comprehensive abatement strategies will be needed to limit global warming. A drastic reduction of black-carbon emissions could provide near-immediate relief with important co-benefits.

The Netherlands has a long and varied history of coastal and river flood management. The anticipation of sea-level rise during the twenty-first century has renewed the push for sustainable solutions to coastal vulnerability.

Changes in continental water stores, largely human-induced, affect sea level. Better hydrological models and observations could clarify the land's role in sea-level variations.

Paradoxically, as the International Polar Year ends we enter its most important phase. Now we must decide — and quickly — which mix of observations to sustain, based on what we have learnt.

In the 2008 Ilulissat Declaration, the five central Arctic states committed themselves to an orderly settlement of any overlapping claims in the Arctic. Nevertheless, the situation in the high north remains a crucial test for the functionality of the law of the sea.

Mars exploration has been guided by the search for water. The more complex quest by Mars Science Laboratory for habitable environments should illuminate the Martian environmental history, and possibly deliver insights into extraterrestrial life.

The 2008 Atlantic hurricane season once again highlighted the challenges awaiting low-lying population centres close to the ocean. In the face of global sea-level rise, unconventional thinking is required to make urban coasts more resilient.

Geo-engineering proposals for mitigating climate change continue to proliferate without being tested. It is time to select and assess the most promising ideas according to efficacy, cost, all aspects of risk and, importantly, their rate of mitigation.