Past global climate changes had strong regional expression. To elucidate their spatio-temporal pattern, we reconstructed past
temperatures for seven continental-scale regions during the past one to two millennia. The most coherent feature in nearly all
of the regional temperature reconstructions is a long-term cooling trend, which ended late in the nineteenth century. At multidecadal to centennial scales, temperature variability shows distinctly different regional patterns, with more similarity within

Of the West Antarctic ice shelves, those in the Amundsen Sea sector have given the most cause for concern. Ocean modelling of the Weddell Sea region, together with a detailed survey of the ice bed morphology, indicates that this region, too, may change soon.

The atmospheric nitrous oxide mixing ratio has increased by 20% since 1750. Given that nitrous oxide is both a long-lived greenhouse gas and a stratospheric ozone-depleting substance, this increase is of global concern. However, the magnitude and geographic distribution of nitrous oxide sources, and how they have changed over time, is uncertain. A key unknown is the influence of the stratospheric circulation which brings air depleted in nitrous oxide to the surface.

The world is undergoing a phenomenally fast wave of urban growth. Research that can help tackle some of the ensuing problems is likely to originate in cities themselves. (Editorial)

The consumption of shallow groundwater with elevated concentrations of arsenic is causing widespread disease in many parts of South and Southeast Asia. In the Bengal Basin, a growing reliance on groundwater sourced below 150-m depth—where arsenic concentrations tend to be lower—has reduced exposure. Groundwater flow simulations have suggested that these deep waters are at risk of contamination due to replenishment with high-arsenic groundwater from above, even when deep water pumping is restricted to domestic use.

World demand for rare-earth elements and the metal yttrium—which are crucial for novel electronic equipment and green-energy technologies—is increasing rapidly. Several types of seafloor sediment harbour high concentrations of these elements.

Afforestation, the conversion of croplands or marginal lands into forests, results in the sequestration of carbon. As a result, afforestation is considered one of the key climate-change mitigation strategies available to governments by the United Nations. However, forests are also less reflective than croplands, and the absorption of incoming solar radiation is greater over afforested areas. Afforestation can therefore result in net climate warming, particularly at high latitudes.

Emissions of CO2 are the main contributor to anthropogenic climate change. Here we present updated information on their present and near-future estimates. We calculate that global CO2 emissions from fossil fuel burning decreased by 1.3% in 2009 owing to the global financial and economic crisis that started in 2008; this is half the decrease anticipated a year ago. If economic growth proceeds as expected, emissions are projected to increase by more than 3% in 2010, approaching the high emissions growth rates that were observed from 2000 to 2008.

Mapping variations in regional sea level changes of different parts of the Indian Ocean could help developing countries better adapt to the effects of climate change, according to a study.