Progress Article

Efforts to control climate change require the stabilization of atmospheric carbon dioxide concentrations. An assessment of the trends in sources and sinks of atmospheric carbon dioxide suggests that the sinks are not keeping up with the increase in carbon dioxide emissions, but uncertainties are still large.

The rapid increase in anthropogenic emissions of greenhouse gases necessitates the consideration of mechanisms for capturing and storing carbon dioxide. Recent work suggests that fluid or gaseous carbon dioxide can be injected into the Earth's crust, and locked up as carbonate minerals to achieve near-permanent and secure sequestration.

Past interglacials can be thought of as a series of natural experiments in which boundary conditions varied considerably. Examination of the palaeoclimate record of the past 800,000 years reveals a large diversity among interglacials in terms of their intensity, duration and internal variability.

Many of the world's deltas are densely populated and intensively farmed. An assessment of recent publications indicates that the majority of these deltas have been subject to intense flooding over the past decade, and that this threat will grow as global sea-level rises and as the deltas subside.

Slab fluids drive mantle melting and return ocean water to the Earth's surface through arc volcanism. New ways of estimating the temperature of slab fluids indicate relatively hot conditions, and hint at a shallow and fast return path for ocean water.

Science and society are faced with two challenges that are inextricably linked: fossil-fuel energy dependence and rising levels of atmospheric carbon dioxide. Coupling of noble gas and carbon chemistry provides an innovative approach to understanding the deep terrestrial carbon cycle.

The Earth's mantle constitutes over 80% of the planet's volume and is a key reservoir in global geochemical cycling. An overview of the progress in understanding the generation of mid-ocean-ridge basalt from mantle melt shows that a variety of processes chemically alter mantle signals in the melt generated at depth before its eruption at the sea floor.

Marine dissolved oragnic matter contains roughly as much organic carbon as all living biota on land and in the oceans combined. New techniques in analytical chemistry show that a significant portion of this material has undergone thermal alteration, either on land or in sediments deep below the sea floor.

The tropics sustain strong coherent variations in wind and precipitation on intraseasonal timescales of 30–60 days. These variations pace the active and break cycles of the monsoons, exerting a direct control on the livelihoods of large populations dependent on rain-fed agriculture. Emerging evidence suggests that heat fluxes from ocean to atmosphere play a fundamental role in driving these intraseasonal oscillations.

European forests are intensively exploited for wood products, yet they are also a potential sink for carbon. European forest inventories combined with timber harvest statistics from sixteen European countries show that between 1950 and 2000 forest biomass increased faster than the amount of timber harvests. Silviculture, which has developed over the past 50 years, can efficiently sequester carbon on timescales of decades, while maintaining forests that meet the demand for wood.

Rivers may be efficient environments for metabolizing terrestrial organic carbon that was previously thought to be recalcitrant, owing to pockets that provide geophysical opportunities by retaining material for longer, and to the adaptation of microbial communities, which has enabled them to exploit the energy that escapes upstream ecosystems.

The tropical belt has been widening over past decades — as estimated from a number of independent lines of evidence — shifting the dry subtropical climate zones polewards around the world.