Anthropogenic-induced changes in nutrient ratios have increased the susceptibility of large temperate lakes to several effects of rising air temperatures and the resulting heating of water bodies. First, warming leads to stronger thermal stratification, thus impeding natural complete water turnover (holomixis), which compensates for oxygen deficits in the deep zones. Second, increased water temperatures and nutrient concentrations can directly favour the growth of harmful algae. Thus, lake-restoration programmes have focused on reducing nutrients to limit toxic algal blooms.

South of Africa, the Agulhas Current retroflects and a portion of its waters flows into the South Atlantic Ocean, typically in the form of Agulhas rings. This flux of warm and salty water from the Indian to the Atlantic Ocean (the Agulhas leakage) is now recognized as a key element in global climate. An Agulhas leakage shutdown has been associated with extreme glacial periods, whereas a vigorous increase has preceded shifts towards interglacials.

Hydrological processes in the humid tropics differ from other regions in having greater energy inputs and faster rates of change, including human-induced change. Human influences on population growth, land use and climate change will profoundly influence tropical hydrology, yet understanding of key hydrological interactions is limited. We propose that efforts to collect tropical data should explicitly emphasize characterizing moisture and energy fluxes from below the ground surface into the atmosphere.

The Tibetan Plateau and surroundings contain the largest number of glaciers outside the polar regions. These glaciers are at the headwaters of many prominent Asian rivers and are largely experiencing shrinkage, which affects the water discharge of large rivers such as the Indus. The resulting potential geohazards merit a comprehensive study of glacier status in the Tibetan Plateau and surroundings. Here we report on the glacier status over the past 30 years by investigating the glacial retreat of 82 glaciers, area reduction of 7,090 glaciers and mass-balance change of 15 glaciers.

Large-scale increases in upper-ocean temperatures are evident in observational records. Several studies have used well-established detection and attribution methods to demonstrate that the observed basin-scale temperature changes are consistent with model responses to anthropogenic forcing and inconsistent with model-based estimates of natural variability. These studies relied on a single observational data set and employed results from only one or two models.

Shale gas can be a powerful tool in combating climate change. However, its exploitation may also lead to undesired environmental effects that can conversely worsen climate change.

Emissions from tropical hydropower are often underestimated and can exceed those of fossil fuel for decades.

redictions of a 40–140% increase in wheat yield by 2050, reported in the UK Climate Change Risk Assessment, are based on a simplistic approach that ignores key factors affecting yields and hence are seriously misleading.

As host to the Rio+20 United Nations Conference on Sustainable Development, Brazil will draw international attention to its policy on climate change, but the measures announced so far are not commensurate with the recently set reduction goal.

In January 2012, the first Climate Change Risk Assessment (CCRA) report was presented to the UK government to inform national adaptation policy. Regarding the agricultural sector, we and our colleagues used a risk-metric approach to assess consequences for crop yield. Writing in Nature Climate Change, Semenov et al. present a critique on the crop yield metric used in our analysis. Although we do not refute the scientific evidence presented, we do question its purpose. (Correspondence)