Letters in 2014

This study shows that the biological impact and footprint of a leakage from a controlled sub-seabed release of carbon dioxide is confined to a few tens of metres, and identifies monitoring strategies for full-scale carbon storage operations.

An analysis of a high-resolution global temperature data set shows that temperate and polar regions are becoming more tropical in their temperature variation profiles, potentially affecting organisms and impacting human agriculture and health.

In the United States, a key goal of states’ climate change policies is to reduce CO₂ emissions from electric power plants. This study shows that specific policy packages significantly shape CO₂ emissions from individual power plants.

The glaciers of the Antarctic Peninsula are experiencing faster melt because of increased temperatures; however, changes in precipitation may offset some of the future melt. This study looks at the relationship between glaciers and climate and finds a representative glacier is more sensitive to temperature change, rather than precipitation change. This indicates that precipitation increases are unlikely to counter the increased melt from warming.

Accounting for natural decadal variability allows better prediction of short-term trends. This study looks at the ability of individual models, which are in phase with the Interdecadal Pacific Oscillation, to simulate the current global warming slowdown. The authors highlight that the current trend could have been predicted in the 1990s with this technique and the need for consistent hindcast skills to allow reliable decadal predictions.

Whether rising temperatures will reduce global soil carbon stocks and enhance climate warming remains uncertain, in part because of a poor understanding of the mechanisms of soil microbial response to warming. Research now shows that microbial growth efficiency is insensitive to temperature change and that the response of microbial respiration to warming is driven by accelerated microbial turnover and enzyme kinetics.

The role of natural decadal variability in the global warming slowdown has been hinted at, but not quantified. This study looks at decadal average surface temperature anomalies for the 1980s, 1990s and 2000s. The results show that decadal variability is a large contributor to temperature trends, but its influence has decreased, from 47% in the 1980s to 27% in the 2000s, as anthropogenic warming has increased.

The global radiative effects of historical cropland expansion are typically estimated as the trade-off between reduced land carbon storage (causing warming) and increased surface albedo (causing cooling). Now research shows that the net atmospheric chemistry effect (−0.11 ± 0.17 W m⁻²) is of comparable magnitude and should also be taken into account.

Biologically relevant metrics of global change are needed for risk assessment, to assess species exposure, and for adaptation planning. This paper presents a new measure of global change velocity that incorporates both climate and land-use change, and explores the implications of the observed velocities for conservation planning in the US.

Africa is sometimes called ‘the burning continent’ owing to the prevalent use of fire for landscape management. This study shows that precipitation changes associated with El Niño/Southern Oscillation help explain fire trends in Africa over the period 2001–2012. However, a shift in land use from savannah to cropland also reduced fire prevalence in the northern half of the continent.

The proposed Keystone XL pipeline to connect Canadian oil sands with US refineries and ports has attracted much controversy. Based on an economic model, this study finds that the biggest emissions impact of the pipeline may be due to its effect of lowering global oil prices and, in turn, increasing global oil consumption (and related emissions). The analysis therefore points to a gap in existing assessments of the Keystone XL project.

European forest disturbance—due to wind, bark beetles and wildfires—has increased in association with climate changes, but future disturbance-response remains highly uncertain. Now, research based on an ensemble of climate change scenarios indicates that an increase in forest disturbance is probable in the coming decades, with implications for forest carbon storage.

The impacts of climate change on certain aspects of the El Niño/Southern Oscillation (ENSO) have been established. However, the change in sea surface temperature, commonly used to represent ENSO amplitude, remained uncertain. Now, the sea surface response is shown to be time-varying, with an increasing trend to 2040 followed by a decreasing trend. The previous uncertainty is attributed to the expectation of unidirectional behaviour and unrealistic model representations.

The Pacific trade winds have strengthened since the late 1990s, and there has been related strengthening of the atmospheric Walker circulation. Although the impacts of these changes are becoming known, their cause has not been identified. This study, using observations and models, shows that warming of the Atlantic sea surface and corresponding displacement of atmospheric pressure centres are key drivers.

This study shows that climate change has the potential to substantially increase undernourishment rates and threaten food security in developing countries through crop damage, but that ozone regulation can significantly offset climate impacts, depending on the scenario. The findings should help policymakers devise optimal strategies for food production under global climate change.

Earth system models do not currently account for unforced variability in land–atmosphere CO₂ flux when simulating the responses of the terrestrial carbon cycle to anthropogenically forced changes in climate and atmosphere. Now, research shows that this unforced variability is larger than the forced response in many areas of the world, precluding detection of the forced carbon-cycle change for decades.

Internal variability in the climate system makes it difficult to determine the rate of regional sea-level rise. This study uses satellite altimetry data and corrects for natural variability to determine the anthropogenic contribution to sea-level rise in the tropical Pacific region.

Reduced soil-carbon storage in response to warming is a potential reinforcing feedback that could enhance climate change. A study now shows that for tropical montane wet forest, long-term warming (represented by an altitudinal gradient) accelerates below-ground carbon processes but has no apparent impact on soil-organic-carbon storage.

Nitrous oxide (N₂O) is a greenhouse gas and an important ozone-depleting substance. Microbial nitrogen cycling in agricultural soils is a major source of atmospheric N₂O. Now, research shows that the capacity of soils to take up N₂O is mostly explained by the abundance and diversity of a newly described N₂O-reducing microbial group.

Historical aerosol forcing from large volcanic eruptions are reconstructed from sulphate deposition measured in ice cores. This study updates these records by using a more extensive collection of Antarctic ice cores, which provide new records and accurate dating of published records. The results show that prior to the year 1500 the reconstructions were either previously overestimating global aerosol forcing by 20–30% or underestimating it by 20–50%. This has implications for estimates of climate sensitivity.