Letters in 2013

Caribou populations that have experienced a relatively stable climatic history have high genetic diversity and occur in regions where climate stability is expected to continue. These findings, based on analyses of molecular data, predicted species distributions and a diffusion model, provide insight into the role of past and future climate change in controlling species’ genetic structure and evolutionary potential.

Studies about early warning signals of a climate tipping point suggest that collective action to avoid a catastrophe will only take place if uncertainty about the threshold for dangerous climate change is reduced. An experiment now finds that behaviour changes dramatically either side of a dividing line for this threshold uncertainty—when uncertainty is only slightly larger, catastrophe is not averted.

The Northern Hemisphere has seen record declines in the summer sea-ice and snow cover at high latitudes, as well as a recent increase in extreme summer events at mid latitudes. The connection between these has been unclear; however, changes in atmospheric circulation attributable to the reduced cryosphere are now shown to be linked to the summer extremes.

Climate change is expected to strengthen the hydrological cycle but this is yet to be conclusively shown. Satellite observations are used to investigate changes in terrestrial evaporation, indicating increases at northern latitudes that are in line with expectations. However, global multidecadal variability is dominated by El Niño/Southern Oscillation cycles.

The combination of climatic warming and wetting can increase the CO₂ sink strength of High Arctic semi-deserts by an order of magnitude, according to a long-term climate manipulation experiment in northwest Greenland. These findings indicate that parts of the High Arctic have the potential to remain a strong carbon sink under future global warming.

The marine environment is under threat from climate change. This study finds that marine reserves can maintain biodiversity and abundance of large-bodied individuals in a warming environment. They also protect against colonization by range-shifting species when compared with fished sites.

Stopping anthropogenic carbon emissions will not result in a sudden decrease in temperature. Earth system models are used to show that there may be an increase in warming after an initial decrease. This is a result of feedbacks from decreased ocean heat uptake, which exceed the cooling from decreased atmospheric CO₂.

There are large uncertainties associated with the projection of climate extremes. This study shows that the uncertainties are mainly due to internal climate variability. However, model projections are consistent when averaged across regions, allowing robust projection of future extremes.

The water chemistry in reef systems can be significantly different from that of the open ocean. Now research based on observations from Bermuda shows that the responses of coral reef communities to ocean acidification could partially offset changes in seawater pH and aragonite saturation.

Predicting species’ chances of survival under climate change requires an understanding of their adaptive potential. Now research into hybridization—one mechanism that could facilitate adaptation—shows that species of the plant genus Pachycladon that survived the Last Glacial Maximum benefited from the transfer of genetic information through hybridization.

The amount of water required for electricity generation is expected to increase as CO₂ emissions are reduced. A capacity expansion model of the Texas electricity grid in the USA demonstrates the trade-offs between CO₂ emissions and water use in designing the power generation mix. Better understanding of the ‘water–energy nexus’ should help to coordinate mitigation and adaptation planning in the energy sector.

The role of temporal discounting in group decisions is poorly understood. A group experiment on collective risk in the context of climate change is used to analyse cooperative behaviour under different timeframes for the realization of the cooperation benefits. Results show that gains that are delayed significantly into the future—intergenerational discounting—markedly diminish cooperation.

Larval stages are particularly vulnerable to environmental changes. The impact of ocean acidification on the digestive processes of sea urchin larvae is shown to decrease efficiency owing to a drop in stomach pH. Despite compensatory feeding, the larval energy budget is likely to be affected.

Mitigation of greenhouse gas emissions often reduces co-emitted air pollutants, with advantages for human health. Avoided mortality from air pollution, a co-benefit of CO₂ abatement, is estimated under global climate change mitigation scenarios to be in the range of US$50–US$380 per tonne of CO₂. This exceeds the projected mitigation costs for 2030 and 2050, and is within the lower range of costs expected in 2100.

A global data set of proxy-based temperature estimates and biome reconstructions is used to assess the ability of eight climate models to simulate the warm environments of the Pliocene. Model results show a substantial cold bias in the Northern Hemisphere. Sensitivity tests identify temporal variability, the temperature difference over the proxy time range, as an important factor in model–data discrepancies, indicating that future comparisons should focus on time slices with the same orbital forcing

Risk maps of climate impacts are potentially useful for targeting efforts to minimize ecological losses. However, most such maps only identify exposure to climate hazards. Now research that also identifies the proportion of intact natural vegetation (as a measure of adaptive capacity) provides global estimates of ecoregional vulnerability to climate change.

The effect of temperature on marine phytoplankton growth strategies, metabolism and composition is studied using a range of techniques. This approach indicates that temperature plays a previously unrecognized, critical role in resource allocation and marine phytoplankton elemental ratios, with implications for biogeochemical cycling.

The extent to which crop pests and pathogens have altered their latitudinal ranges in response to climate change remains largely unknown. Now observations of hundreds of pests and pathogens reveal an average poleward shift of 2.7±0.8 km yr⁻¹ since 1960, supporting the hypothesis of climate-driven pest movement.

Using computer simulations, this study quantifies the potential effect of ocean acidification on marine biogenic sulphur emissions and the resulting feedback mechanisms on future climate. It emphasizes that a reduction of anthropogenic carbon dioxide emissions is not only necessary to limit the negative effects of ocean acidification on marine life, but also to avoid amplified climate warming due to changes in biogenic sulphur production.

Flood losses in coastal cities will rise due to increasing populations and assets. Research now quantifies average losses in the 136 largest coastal cities. Estimated at approximately US$6 billion in 2005, average annual losses could increase to US$52 billion by 2050 on the basis of projected socio-economic change alone. If climate change and subsidence are also considered, current protection will need to be upgraded to avoid unacceptable losses.