ALBERT

Description: Vertical and latitudinal changes in the stratospheric ozone in the post-chlorofluorocarbon (CFC) era are investigated using simulations of the recent past and the 21st century with a coupled chemistry-climate model. Model results reveal that, in the 2060s when the stratospheric halogen loading is projected to return to its 1980 values, the extratropical column ozone is significantly higher than that in 1975–1984, but the tropical column ozone does not recover to 1980 values. Upper and lower stratospheric ozone changes in the post-CFC era have very different patterns. Above 15 hPa ozone increases almost latitudinally uniformly by 6 Dobson Unit (DU), whereas below 15 hPa ozone decreases in the tropics by 8 DU and increases in the extratropics by up to 16 DU. The upper stratospheric ozone increase is a photochemical response to greenhouse gas induced strong cooling, and the lower stratospheric ozone changes are consistent with enhanced mean advective transport due to a stronger Brewer-Dobson circulation. The model results suggest that the strengthening of the Brewer-Dobson circulation plays a crucial role in ozone recovery and ozone distributions in the post-CFC era.

Description: Vertical and latitudinal changes in the stratospheric ozone in the post-chlorofluorocarbon (CFC) era are investigated using simulations of the recent past and the 21st century with a coupled chemistry-climate model. Model results reveal that, in the 2060s when the stratospheric halogen loading is projected to return to its 1980 values, the extratropical column ozone is significantly higher than that in 1975–1984, but the tropical column ozone does not recover to 1980 values. Upper and lower stratospheric ozone changes in the post-CFC era have very different patterns. Above 15 hPa ozone increases almost latitudinally uniformly by 6 Dobson Unit (DU), whereas below 15 hPa ozone decreases in the tropics by 8 DU and increases in the extratropics by up to 16 DU. The upper stratospheric ozone increase is a photochemical response to greenhouse gas induced strong cooling, and the lower stratospheric ozone changes are consistent with enhanced mean advective transport due to a stronger Brewer-Dobson circulation. The model results suggest that the strengthening of the Brewer-Dobson circulation plays a crucial role in ozone recovery and ozone distributions in the post-CFC era.

Description: Black carbon (BC) is an important atmospheric constituent as an air pollutant and as a climate forcer. To our knowledge, field measurements of BC have not been reported over the South China Sea. Observations of light-absorption coefficients (σabs) and BC concentrations by Aethalometer were conducted on Yongxing Island in the South China Sea and at five continental sites in the Pearl River delta (PRD) region, South China, in two periods: 16 May–20 June 2008 in the rainy season and 12 December 2008–8 January 2009 in the dry season. At the oceanic site, the daily average BC concentrations varied from 0.28 to 2.14 μg m−3 and variations of BC were small between the two periods (0.67 in the dry season sampling period and 0.54 μg m−3 in the rainy season sampling period). Similarly, little difference in BC level was found at a rural site in PRD between the two sampling periods (2.88 and 2.62 μg m–3). At the PRD urban sites, the daily average concentration of BC ranged from 1.56 to 37.9 μg m−3, higher in the dry season sampling period (12.31 μg m–3) and lower in the rainy season sampling period (6.17 μg m–3). The observed average σabs values in rainy vs. dry season sampling periods are 119 vs. 62 Mm−1 at the PRD urban sites, 29 vs. 26 Mm−1 at the PRD background site, and 8.4 vs. 7.2 Mm−1 at the marine site. At urban/suburban PRD sites, BC was observed to have a diurnal pattern of higher concentrations at night and at the urban sites a small peak in the early morning rush hour.

Description: Modeling fire as an integral part of an Earth system model (ESM) is vital for quantifying and understanding fire-climate-vegetation interactions on a global scale and from an Earth system perspective. In this study, we introduce to the Community Earth System Model (CESM) the new global fire parameterization proposed by Li et al. (2012), now with a more realistic representation of the anthropogenic impacts on fires, with a parameterization of peat fires, and with other minor modifications. The improved representation of the anthropogenic dimension includes the first attempt to parameterize agricultural fires, the economic influence on fire occurrence, and the socioeconomic influence on fire spread in a global fire model; also an alternative scheme for deforestation fires. The global fire parameterization has been tested in CESM1's land component model CLM4 in a 1850–2004 transient simulation, and evaluated against the satellite-based Global Fire Emission Database version 3 (GFED3) for 1997–2004. The simulated 1997–2004 average global totals for the burned area and fire carbon emissions in the new fire scheme are 338 Mha yr−1 and 2.1 Pg C yr−1. Its simulations on multi-year average burned area, fire seasonality, fire interannual variability, and fire carbon emissions are reasonable, and show better agreement with GFED3 than the current fire scheme in CESM1 and modified CTEM-FIRE. Moreover, the new fire scheme also estimates the contributions of global fire carbon emissions from different sources. During 1997–2004, the contributions are 8% from agricultural biomass burning, 27% from tropical deforestation and degradation fires, 5% from global peat fires (3.7% from tropical peat fires), and 60% from other fires, which are close to previous assessments based on satellite data, government statistics, or other information sources. In addition, we investigate the importance of direct anthropogenic influence (anthropogenic ignitions and fire suppression) on global fire regimes during 1850–2004, using CESM1 with the new fire scheme. Results show that the direct anthropogenic impact is the main factor driving the trends of global burned area in the whole period and fire carbon emissions only before ~ 1870.

Description: Fire is the primary terrestrial ecosystem disturbance agent on a global scale. It affects the net carbon balance of global terrestrial ecosystems by emitting carbon directly and immediately to the atmosphere from biomass burning (i.e., the fire direct effect), and by changing net ecosystem productivity and land-use carbon loss in post-fire regions due to biomass burning and fire-induced vegetation mortality (i.e., the fire indirect effect). Here, we provide the first quantitative assessment of the impact of fire on the net carbon balance of global terrestrial ecosystems during the 20th century, and investigate the roles of fire direct and indirect effects. This was done by quantifying the difference between the 20th century fire-on and fire-off simulations with the NCAR Community Land Model CLM4.5 as model platform. Results show that fire decreases the net carbon gain of global terrestrial ecosystems by 1.0 Pg C yr–1 averaged across the 20th century, as a result of the fire direct effect (1.9 Pg C yr–1) partly offset by the indirect effect (−0.9 Pg C yr–1). Fire generally decreases the average carbon gains of terrestrial ecosystems in post-fire regions, which is significant over tropical savannas and some North American and East Asian forests. The general decrease of carbon gains in post-fire regions is because the fire direct and indirect effects have similar spatial patterns but with opposite function and the former (which decreases the carbon gain of land) is generally stronger. Moreover, the effect of fire on net carbon balance significantly declines prior to ~1970 with a trend of 8 Tg C yr–1 due to increasing fire indirect effect, and increases afterward with a trend of 18 Tg C yr–1 due to increasing fire direct effect.

Description: Biomass burning impacts vegetation dynamics, biogeochemical cycling, atmospheric chemistry, and climate, with sometimes deleterious socio-economic impacts. Under future climate projections it is often expected that the risk of wildfires will increase. Our ability to predict the magnitude and geographic pattern of future fire impacts rests on our ability to model fire regimes, either using well-founded empirical relationships or process-based models with good predictive skill. A large variety of models exist today and it is still unclear which type of model or degree of complexity is required to model fire adequately at regional to global scales. This is the central question underpinning the creation of the Fire Model Intercomparison Project – FireMIP, an international project to compare and evaluate existing global fire models against benchmark data sets for present-day and historical conditions. In this paper we summarise the current state-of-the-art in fire regime modelling and model evaluation, and outline what lessons may be learned from FireMIP.

Description: The shrub Artemisia halodendron and the annual herb Agriophyllum squarrosum, which typically co-occur in a mobile sandy habitat in eastern inner Mongolia, China, were used to determine whether the presence of A. halodendron influences seed deposition and seedling recruitment of A. squarrosum under and around the shrub canopy in relation to wind direction, sampling position (windward vs. leeward sides) and distance from the shrub. The numbers of seeds deposited, seedlings emerged, and individuals recruited of A. squarrosum around adult shrubs were sampled along four transects aligned to the four main wind directions at 0.5, 1, 2, 3, 4.5 and 6 m from the shrub base on both windward and leeward sides of each transect. Spatial pattern of seed deposition was strongly altered by the presence of shrubs, but effects varied with wind direction, sampling position and distance from shrubs. Significantly more seeds tended to deposit on the leeward than on the windward sides in all four transects, with the exception of transects along the least prevailing wind direction. The presence of shrubs as nursing plants caused a marked variation in seed deposition across sampling locations, but this effect was detected only in the most, secondary and third most prevailing wind directions, but not in the least prevailing wind direction. In general, the shrub’s influence was within a 2 m radius from the shrub, despite some differences among transects. Although seed bank density had no direct effect on A. squarrosum recruitment patterns, it contributed to the observed variation in recruitment indirectly through density-dependent emergence of seedlings. Our findings provide further evidence of shrubs as a source of spatial heterogeneity in seed availability and thereby a common factor determining population dynamics of understorey herbaceous species.

Description: The temperature variations caused by additive tectonic stress has been studied to explain its relationship with the seismic fault sliding of the Abruzzo M = 6.3 Earthquake in April 2009. According to the periodic changes of the additive tectonic stress caused by the celestial tide-generating force, the temperature variations before and after the earthquake have been analyzed based on the temperature data from National Centers for Environmental Prediction (NCEP). The figures of temperature variations clearly show that the abnormal increasing of the temperature has resulted from seismic fault sliding. Based on this method, it is possible to forewarn short-impending earthquakes.

Description: Chinese loess sequences are interpreted as a reliable record of the past variation of the East Asian monsoon regime through the alternation of loess and paleosols units, dominated by the winter and summer monsoon, respectively. Different proxies have been used to describe this system, mostly geophysical, geochemical or sedimentological. Terrestrial mollusks are also a reliable proxy of past environmental conditions and are often preserved in large numbers in loess deposits. The analysis of the mollusk remains in the Luochuan sequence, comprising L5 loess to S0 soil, i.e. the last 500 ka, shows that for almost all identified species, the abundance is higher at the base of the interval (L5 to L4) than in the younger deposits. Using the present ecological requirements of the identified mollusk species in the Luochuan sequence allows the definition of two main mollusk groups varying during the last 500 kyr. The cold-aridiphilous individuals indicate the so-called Asian winter monsoon regime and predominantly occur during glacials, when dust is deposited. The thermal-humidiphilous mollusks are prevalent during interglacial or interstadial conditions of the Asian summer monsoon, when soil formation takes place. In the sequence, three events with exceptionally high abundance of the Asian summer monsoon indicators are recorded during the L5, L4 and L2 glacial intervals, i.e., at about 470, 360 and 170 kyr, respectively. The L5 and L4 events appear to be the strongest (high counts). Similar variations have also been identified in the Xifeng sequence, distant enough from Luochuan, but also in Lake Baikal further North, to suggest that this phenomenon is regional rather than local. The indicators of the summer monsoon within the glacial intervals imply a strengthened East-Asian monsoon interpreted as corresponding to marine isotope stages 6, 10 and 12, respectively. The L5 and L2 summer monsoons are coeval with Mediterranean sapropels S12 and S6, which characterize a strong African summer monsoon with relatively low surface water salinity in the Indian Ocean. Changes in the precipitation regime could correspond to a response to a particular astronomical configuration (low obliquity, low precession, summer solstice at perihelion) leading to an increased summer insolation gradient between the tropics and the high latitudes and resulting in enhanced atmospheric water transport from the tropics to the African and Asian continents. However, other climate drivers such as reorganization of marine and atmospheric circulations, tectonic, and the extent of the Northern Hemisphere ice sheet are also discussed.

Description: Soil organic carbon (SOC) plays a vital role as both a sink for and source of atmospheric carbon. Revegetation of degraded arable land in China is expected to increase soil carbon sequestration, but the role of perennial legumes on soil carbon stocks in semiarid areas has not been quantified. In this study, we assessed the effect of alfalfa (Medicago sativa L.) and two locally adapted forage legumes, bush clover (Lespedeza davurica S.) and milk vetch (Astragalus adsurgens Pall.) on the SOC concentration and SOC stock accumulated annually over a 2 m soil profile, and to estimate the long-term potential for SOC sequestration in the soil under the three forage legumes. The results showed that the concentration of SOC of the bare soil decreased slightly over the 7 years, while 7 years of legume growth substantially increased the concentration of SOC over the 0–2.0 m soil depth measured. Over the 7 year growth period the SOC stocks increased by 24.1, 19.9 and 14.6 Mg C ha−1 under the alfalfa, bush clover and milk vetch stands, respectively, and decreased by 4.2 Mg C ha−1 under bare soil. The sequestration of SOC in the 1–2 m depth of soil accounted for 79, 68 and 74 % of SOC sequestered through the upper 2 m of soil under alfalfa, bush clover and milk vetch, respectively. Conversion of arable land to perennial legume pasture resulted in a significant increase in SOC, particularly at soil depths below 1 m.