Letters in 2013

Albedo is a key component in the energy budget of the Arctic region, and a thorough understanding of it is essential for climate modelling. An analysis of the changes in Arctic sea-ice from 1982 to 2009 indicates that late summer sea-ice albedo is becoming dimmer. The rate of albedo decrease is shown to be accelerating over the study period.

Research that combines all available studies of biological responses to regional and global climate change shows that 81–83% of all observations were consistent with the expected impacts of climate change. These findings were replicated across taxa and oceanic basins.

Earth system models (ESMs) generally have crude representations of the responses of soil carbon responses to changing climate. Now an ESM that explicitly represents microbial soil carbon cycling mechanisms is able to simulate carbon pools that closely match observations. Projections from this model produce a much wider range of soil carbon responses to climate change over the twenty-first century than conventional ESMs.

The long-term loss of carbon from thawing permafrost in Northeast Greenland is quantified for 1996–2008 by repeated sediment sampling and incubation. Although the active layer has increased by >1 cm per year, there has not been a detectable decline in carbon stocks. Laboratory studies highlight the potential for fast carbon mobilization under aerobic conditions, but indicate that carbon at near-saturated conditions may remain largely immobilized for decades.

The Iberian lynx has suffered severe population declines in the twentieth century. An ecological modelling study that accounts for the effects of climate change, prey availability and management intervention now shows that lynx are likely to become extinct in the wild in the next 50 years. However, a carefully planned reintroduction program could avert extinction this century.

Increasing volatility in food markets and the rising incidence of climatic extremes could lead to more frequent spikes in food prices. A global assessment of the reliability of crop simulations in reproducing past failures in major crop types suggests that seasonal forecasts can be useful for monitoring global food production.

Extreme weather, rising seas and degraded coastal ecosystems all play a part in escalating the risks that coastal regions are exposed to. Now research into hazards facing the contiguous USA indicates that the likelihood and magnitude of losses can be reduced by intact reefs and coastal vegetation.

Climate change cooperation has been limited by the lack of sanctioning mechanisms to deal with those who fail to abide by agreements. Research now shows that a bottom-up process, in which parties create local institutions that punish free-riders, promotes widespread cooperation as opposed to the traditional top-down approach that builds global institutions.

Competing influences on tropical forest productivity, such as changes in temperature, light and precipitation, can be difficult to disentangle. Now, analysis of how clouds, temperature and precipitation affect flower production in two contrasting tropical forests indicates that temperature is a critically important variable for tropical forest flower production.

Little is known about the sensitivity of Antarctic krill, a key part of the food chain, to ocean acidification. A circumpolar risk map of krill hatching success is presented for projected ocean acidification levels. Important krill recruitment habitats are likely to become high-risk this century, with the possibility of collapse of the krill population by 2300 without mitigation of CO₂ emissions.

The impact of climate change on the global hydrological cycle is unclear, with land precipitation and river discharges not increasing as expected. This discrepancy is investigated and tropospheric aerosols are found to have weakened the hydrological cycle between the 1950s and 1980s. The increase in greenhouse gases since the 1980s strengthened the cycle, indicating a further increase in precipitation if the current trend continues.

The El Niño/Southern Oscillation exhibits considerable natural variability on interdecadal to centennial timescales making it difficult to understand how climate change affects it. A reconstruction now shows there has been anomalously high activity in the late twentieth century, relative to the past seven centuries. This is suggestive of a response to global warming, and will provide constraints to improve climate models and projections.

Climate change mitigation has slowed down as major emitters face economic stagnation. Research now shows that the average cost to society of an additional tonne of carbon dioxide emissions tends to increase during recessions as the impact occurs in a poorer world. This suggests that climate change mitigation should be a priority in a low-growth situation.

Flood risk is expected to increase as the climate warms. This study, for the first time, uses several climate models to estimate the global risk of flooding at the end of the century. Projections show a large increase in flood frequency in some areas, whereas other regions can expect a decrease. Vulnerability is dependent on the degree of warming and the interannual variability in precipitation.

Large standardized model intercomparison projects enable the quantification of uncertainty in projecting the impacts of climate change. One of the largest studies so far indicates that individual crop models are able to simulate wheat yields accurately under a range of environments, but that differences between crop models are a major source of uncertainty.

Climate-induced changes in phenology have the potential to push trophic relationships out of synchrony, but evidence of this phenomenon is scant, particularly in the Arctic. A long-term (1996–2009), spatially replicated data set from high-Arctic Greenland now indicates a climate-associated shortening of the flowering season, and a concomitant decline in flower visitor abundance.

Climatic warming is intensifying the global water cycle, and is projected to increase rainfall variability. Higher interannual variability in rainfall is shown to reduce tree cover in the wet tropics, but may promote expansion of cover in tropical dry lands.

The response of the carbon cycle to climate change, including carbon fluxes, is now shown to be the second largest source of uncertainty in projections of temperature. A simplified climate model using temperature records and historical estimates of CO₂ concentrations demonstrates that considering these two factors together reduces uncertainty further than treating them as individual parameters.

Climate change is expected to increase the intensity of precipitation in many regions. Experiments show that small increases in precipitation intensity, but not total amount, can lead to deeper penetration of water into the soil, leading to greater woody plant growth at the cost of grasses in a savannah system.

Climate change is altering the seasonal distribution, interannual variability and overall magnitude of precipitation. A new global measure of precipitation seasonality is proposed, and application of this method to observations from the tropics shows that increases in variability were accompanied by shifts in seasonal magnitude, timing and duration.