Letters

Progress towards reaching an international climate agreement has been painfully slow and fraught with difficulty. This work presents a newly developed game theoretic model aimed at the conceptual clarification of some key obstacles in current international negotiations. The model is then used to suggest possible solutions to these obstacles.

Climate variability in the Southern Hemisphere is dominanted by the Southern Annular Mode, which influences temperatures and latitudinal rainfall distribution. This work reconstructs its annual variability since the year 1000. The authors find that a positive trend since the 1940s is reproduced by climate model simulations with representative greenhouse gas forcings and ozone depletion. Early trends indicate a teleconnection to tropical Pacific climate, which may need to be considered in projections under climate change.

Inland waters collect organic matter from the surrounding land, some of which accumulates to form an important sediment reservoir for organic carbon. Research now shows that rising temperatures in the tropics increase the rate of mineralization and greenhouse gas production from tropical lake sediments by 2.4–4.5 times more than in sub-arctic lakes.

The Wilkes ice sheet in East Antarctica, which lies on bedrock below sea level, is sensitive to climate change but its stability and potential contribution to sea-level rise has not been comprehensively assessed. This study uses topographic data and ice-dynamic simulations to show that removal of a specific coastal ice volume destabilizes the ice sheet, leading to discharge of the entire Wilkes Basin and global sea-level rise of 3–4 m.

Global warming is non-uniform in time and space, but to understand potential impacts we need better understanding of its evolution. This work breaks down the warming trend and finds that it began in the subtropical and subpolar regions of the Northern Hemisphere, followed by the subtropical region of the Southern Hemisphere. The warming bands in the Northern Hemisphere expanded during the period 1950–1985 and merged to cover the entire hemisphere.

Selecting economically viable forest management strategies that deliver carbon storage and biodiversity benefits can be a difficult task. Now, research in the western Andes of Colombia shows that naturally regenerating forests can quickly accumulate carbon and support diverse ecological communities at minimal cost.

The impact of ocean warming on coral larvae survival and dispersal is investigated using a dynamic model. The authors find that globally most reefs will experience large increases in the local retention of larvae, which make populations more responsive to local conservation efforts. However, increased larvae retention will also weaken connectivity between populations, which may affect recovery if a local population is severely disturbed.

The South Asian summer monsoon has an impact on over one billion people. This study applies statistical techniques to precipitation observations (over the period 1951–2011) and finds significant increases in daily precipitation variability, the frequency of dry spells and the intensity of wet spells, whereas dry spell intensity decreases.

Sea-level rise represents a threat to intertidal oyster reefs and knowledge of their growth rates is needed to quantify the threat. This study presents direct measurements of intertidal oyster reef growth and develops an empirical model of reef accretion. The authors show that previous measurements underestimate growth—the reefs studied here seem able to keep up with projected sea-level rise.

There has been a rapid growth in the use of natural gas and biofuels. This study evaluates energy technologies against climate targets and shows that the impact of technologies that result in the emission of both methane and carbon dioxide depends on their time of use. The changes in climate impacts over time are large, with several technologies that are widely considered mitigation options becoming unfavourable within two decades.

The forests of the Rocky Mountains of North America are suffering the effects of a climate-exacerbated bark-beetle epidemic. This study shows that the transpiration loss due to widespread tree death is affecting stream flow-generating processes at watershed scale, with potential implications for water quality.

Prediction of seasonal Arctic sea-ice extent is of increased interest as the region opens up due to climate change. This work uses spring melt-pond area to forecast the Arctic sea-ice minimum in September. This proves accurate, as increasing melt-ponds reduce surface albedo, allowing more melt to occur, creating a positive feedback mechanism.

Life-cycle assessment of biofuel carbon emissions does not usually take into account the potential for soil carbon loss resulting from crop residue removal. Now estimates of CO₂ emissions due to corn residue removal across the US Corn Belt indicate that the emissions from soil carbon loss could push total emissions above the US legislative mandate.

The direct effects of land-cover change on surface climate are increasingly well understood, but fewer studies have investigated the consequences of the trend towards more intensive land management practices. Now, research investigating the biophysical effects of temperate land-management changes reveals a net warming effect of similar magnitude to that driven by changing land cover.

Laboratory experiments have shown that the behaviour of reef fishes can be impaired by the CO₂ levels projected to occur in the ocean by the end of this century. Research now shows that reef fishes at natural volcanic CO₂ seeps also exhibit behavioural abnormalities, and that behaviour does not acclimate with extended exposure to high CO₂. Fish communities are therefore likely to face a serious threat from CO₂-induced behavioural abnormalities in the future as ocean acidification becomes widespread.

Reductions in the protein and nitrogen content of plants grown under enhanced atmospheric CO₂ concentrations could adversely affect the quality of food grown in the future, but the mechanisms of change remain unclear. Now research investigating plant responses to enhanced levels of atmospheric CO₂ under field conditions finds that wheat nitrate assimilation was slower for elevated CO2 than for ambient CO₂.

The response of terrestrial ecosystems to climate change remains a large source of uncertainty in the global carbon budget. Now results from a ten-year ecological manipulation experiment in the Mojave Desert provide direct evidence that CO₂ fertilization can substantially increase ecosystem carbon storage in arid ecosystems.

A synthesis of findings from 92 forests in different climate zones reveals that nutrient availability plays a crucial role in determining forest carbon balance, primarily through its influence on respiration rates. These findings challenge the validity of assumptions used in most global coupled carbon-cycle climate models.

Increasing concentrations of atmospheric particles are expected to impact Northern Hemisphere mid-latitude precipitation and temperature. This study finds that there is little evidence that aerosol concentrations affect land precipitation in the region, which they attribute to changes in observational techniques that increased measured values at the time aerosols were expected to suppress precipitation.

Palaeoclimate temperature records are dominated by Northern Hemisphere reconstructions. This study introduces a new Southern Hemisphere millennial temperature reconstruction from terrestrial and oceanic proxy records. This highlights the asynchronicity of temperature fluctuations across the two hemispheres, which should be taken into consideration in climate models and projections.