Filters
Results 1 - 10 of 79
Results 1 - 10 of 79.
Search took: 0.028 seconds
| Sort by: date | relevance |
[en] Deforestation in Amazon is expected to decrease evapotranspiration (ET) and to increase soil moisture and river discharge under prevailing energy-limited conditions. The magnitude and sign of the response of ET to deforestation depend both on the magnitude and regional patterns of land-cover change (LCC), as well as on climate change and CO2 levels. On the one hand, elevated CO2 decreases leaf-scale transpiration, but this effect could be offset by increased foliar area density. Using three regional LCC scenarios specifically established for the Brazilian and Bolivian Amazon, we investigate the impacts of climate change and deforestation on the surface hydrology of the Amazon Basin for this century, taking 2009 as a reference. For each LCC scenario, three land surface models (LSMs), LPJmLDGVM, INLAND-DGVM and ORCHIDEE, are forced by bias-corrected climate simulated by three general circulation models (GCMs) of the IPCC 4. Assessment Report (AR4). On average, over the Amazon Basin with no deforestation, the GCM results indicate a temperature increase of 3.3 degrees C by 2100 which drives up the evaporative demand, whereby precipitation increases by 8.5%, with a large uncertainty across GCMs. In the case of no deforestation, we found that ET and runoff increase by 5.0 and 14 %, respectively. However, in south-east Amazonia, precipitation decreases by 10% at the end of the dry season and the three LSMs produce a 6% decrease of ET, which is less than precipitation, so that runoff decreases by 22%. For instance, the minimum river discharge of the Rio Tapajos is reduced by 31% in 2100. To study the additional effect of deforestation, we prescribed to the LSMs three contrasted LCC scenarios, with a forest decline going from 7 to 34% over this century. All three scenarios partly offset the climate-induced increase of ET, and runoff increases over the entire Amazon. In the southeast, however, deforestation amplifies the decrease of ET at the end of dry season, leading to a large increase of runoff (up to + 27% in the extreme deforestation case), offsetting the negative effect of climate change, thus balancing the decrease of low flows in the Rio Tapajos. These projections are associated with large uncertainties, which we attribute separately to the differences in LSMs, GCMs and to the uncertain range of deforestation. At the subcatchment scale, the uncertainty range on ET changes is shown to first depend on GCMs, while the uncertainty of runoff projections is predominantly induced by LSM structural differences. By contrast, we found that the uncertainty in both ET and runoff changes attributable to uncertain future deforestation is low. (authors)
Journal
Hydrology and Earth System Sciences (Online); ISSN 1607-7938; 
; v. 21(no.3); p. 1455-1475
; v. 21(no.3); p. 1455-1475
[en] Most emission metrics have previously been inconsistently estimated by including the climate-carbon feedback for the reference gas (i.e. CO2) but not the other species (e.g. CH4). In the fifth assessment report of the IPCC, a first attempt was made to consistently account for the climate-carbon feedback in emission metrics. This attempt was based on only one study, and therefore the IPCC concluded that more research was needed. Here, we carry out this research. First, using the simple Earth system model OSCAR v2.2, we establish a new impulse response function for the climate-carbon feedback. Second, we use this impulse response function to provide new estimates for the two most common metrics: global warming potential (GWP) and global temperature-change potential (GTP). We find that, when the climate-carbon feedback is correctly accounted for, the emission metrics of non-CO2 species increase, but in most cases not as much as initially indicated by IPCC. We also find that, when the feedback is removed for both the reference and studied species, these relative metric values only have modest changes compared to when the feedback is included (absolute metrics change more markedly). Including or excluding the climate-carbon feedback ultimately depends on the user's goal, but consistency should be ensured in either case. (authors)
Journal
Earth System Dynamics; ISSN 2190-4979; ; v. 8(no.2); p. 235-253
; v. 8(no.2); p. 235-253
[en] Complete text of publication follows: In their viewpoint, van Groeningen et al. (1) argue that a 'nitrogen dilemma' could reduce the feasibility of the global increase in soil organic carbon (SOC) stocks targeted by the 4 per 1000 Initiative (2) and suggest the need for a 'spatially diversified strategy' for climate change mitigation from agricultural soils. More specifically, they point that the 'increase in plant N uptake required to meet the 4 per 1000 goal is unrealistic' given policies targeting reductions in N surpluses from intensive agriculture. The 4 per 1000 target provides a guideline for locally increasing SOC stocks in the top soil by 0.4% per year, implying an annual SOC sequestration rate proportional to the initial SOC stock. With this aspirational target, degraded soils with low SOC stocks need to sequester less carbon and, hence, immobilize less N and P than soils rich in organic matter. Therefore, the 4 per 1000 target is spatially differentiated in terms of nitrogen and phosphorus requirements. Global reactive N (Nr) availability in agricultural ecosystems is large (ca. 300 Tg Nr per year (7)), but unevenly distributed. In most intensive agricultural systems, since Nr and P are in excess, additional SOC sequestration, for example, through cover crops (3) could reduce environmental pollution thereby matching environmental policies targeting reductions in Nr and P surpluses. In contrast, in extensive cropping systems with low initial SOC stocks, the modest Nr and P supplies required for SOC sequestration at an annual rate of 0.4% could be provided by biological N fixation (BNF) from legumes, with possible cobenefits for climate change adaptation. (4) BNF could be restricted by low P bioavailability in some soils, but symbiotic N2 fixation plants possess an advantage in P acquisition especially in warm climates,for example, through root phosphatase (5) and legume trees and shrubs can mobilize phosphorus from deep soil layers. Additionally, recycling organic fertilizers derived from livestock or urban wastes (6) could help counter N and P deficiencies. In the long term, since global N:P stoichiometry is increasing under human influence (7) P limitation could become more critical for global SOC sequestration than N limitation. In most cases, providing Nr and P through inorganic fertilizers applications only would be too expansive (ca. 170 USD per Mg of C carbon sequestered (8)) and would lead to additional Nr release to the environment. On a global scale, soil erosion by water induces annual nutrients losses (23-42 Mt (megaton) N and 15-26 Mt P) in agricultural land, which are of the same order of magnitude than annual fertilizer application rates. (9) Soils nutrients lost by erosion need to be replaced through fertilization at an economic cost, which is too high in poor regions such as sub-Saharan Africa. Limiting erosion and land degradation, through the 4 per 1000 strategy, could preserve a source of nutrients both for plants and for the buildup of SOM and thereby reduce the needs for additional fertilizer inputs
Journal
Environmental Science and Technology; ISSN 0013-936X; ; v. 51(no.20); p. 11502
; v. 51(no.20); p. 11502
[en] Background: Europe has warmed more than the global average (land and ocean) since pre-industrial times, and is also projected to continue to warm faster than the global average in the twenty-first century. According to the climate models ensemble projections for various climate scenarios, annual mean temperature of Europe for 2071-2100 is predicted to be 1-5.5 degrees C higher than that for 1971-2000. Climate change and elevated CO2 concentration are anticipated to affect grassland management and livestock production in Europe. However, there has been little work done to quantify the European-wide response of grassland to future climate change. Here we applied ORCHIDEE-GM v2.2, a grid-based model for managed grassland, over European grassland to estimate the impacts of future global change. Results: Increases in grassland productivity are simulated in response to future global change, which are mainly attributed to the simulated fertilization effect of rising CO2. The results show significant phenology shifts, in particular an earlier winter-spring onset of grass growth over Europe. A longer growing season is projected over southern and southeastern Europe. In other regions, summer drought causes an earlier end to the growing season, overall reducing growing season length. Future global change allows an increase of management intensity with higher than current potential annual grass forage yield, grazing capacity and livestock density, and a shift in seasonal grazing capacity. We found a continual grassland soil carbon sink in Mediterranean, Alpine, North eastern, South eastern and Eastern regions under specific warming level (SWL) of 1.5 and 2 degrees C relative to pre-industrial climate. However, this carbon sink is found to saturate, and gradually turn to a carbon source at warming level reaching 3.5 degrees C. Conclusions: This study provides a European-wide assessment of the future changes in productivity and phenology of grassland, and their consequences for the management intensity and the carbon balance. The simulated productivity increase in response to future global change enables an intensification of grassland management over Europe. However, the simulated increase in the interannual variability of grassland productivity over some regions may reduce the farmers' ability to take advantage of the increased long-term mean productivity in the face of more frequent, and more severe drops of productivity in the future. (authors)
Journal
Carbon Balance and Management; ISSN 1750-0680; ; v. 12; p. 1-21
; v. 12; p. 1-21
[en] Understanding the variations in global land carbon uptake, and their driving mechanisms, is essential if we are to predict future carbon-cycle feedbacks on global environmental changes. Satellite observations of vegetation greenness have shown consistent greening across the globe over the past three decades. Such greening has driven the increasing land carbon sink, especially over the growing season in northern latitudes. On the other hand, interannual variations in land carbon uptake are strongly influenced by El Nino-Southern Oscillation (ENSO) climate variations. Marked reductions in land uptake and strong positive anomalies in the atmospheric CO2 growth rates occur during El Nino events. Here we use the year 2015 as a natural experiment to examine the possible response of land ecosystems to a combination of vegetation greening and an El Nino event. The year 2015 was the greenest year since 2000 according to satellite observations, but a record atmospheric CO2 growth rate also occurred due to a weaker than usual land carbon sink. Two atmospheric inversions indicate that the year 2015 had a higher than usual northern land carbon uptake in boreal spring and summer, consistent with the positive greening anomaly and strong warming. This strong uptake was, however, followed by a larger source of CO2 in the autumn. For the year 2015, enhanced autumn carbon release clearly offset the extra uptake associated with greening during the summer. This finding leads us to speculate that a long-term greening trend may foster more uptakes during the growing season, but no large increase in annual carbon sequestration. For the tropics and Southern Hemisphere, a strong transition towards a large carbon source for the last 3 months of 2015 is discovered, concomitant with El Nino development. This transition of terrestrial tropical CO2 fluxes between two consecutive seasons is the largest ever found in the inversion records. The strong transition to a carbon source in the tropics with the peak of El Nino is consistent with historical observations, but the detailed mechanisms underlying such an extreme transition remain to be elucidated. (authors)
Journal
Atmospheric Chemistry and Physics; ISSN 1680-7316; ; v. 17(no.22); p. 1-17
; v. 17(no.22); p. 1-17
[en] Spatial patterns and temporal trends of nitrogen (N) and phosphorus (P) deposition are important for quantifying their impact on forest carbon (C) uptake. In a first step, we modeled historical and future change in the global distributions of the atmospheric deposition of N and P from the dry and wet deposition of aerosols and gases containing N and P. Future projections were compared between two scenarios with contrasting aerosol emissions. Modeled fields of N and P deposition and P concentration were evaluated using globally distributed in situ measurements. N deposition peaked around 1990 in European forests and around 2010 in East Asian forests, and both increased sevenfold relative to 1850. P deposition peaked around 2010 in South Asian forests and increased 3.5-fold relative to 1850. In a second step, we estimated the change in C storage in forests due to the fertilization by deposited N and P (Δ C-v (dep)), based on the retention of deposited nutrients, their allocation within plants, and C:N and C:P stoichiometry. Δ C-v (dep) for 1997-2013 was estimated to be 0.27 ± 0.13 Pg C year-1 from N and 0.054 ± 0.10 Pg C year-1 from P, contributing 9% and 2% of the terrestrial C sink, respectively. Sensitivity tests show that uncertainty of δ C-v (dep) was larger from P than from N, mainly due to uncertainty in the fraction of deposited P that is fixed by soil. Δ C-P (dep) was exceeded by δ C-N (dep) over 1960-2007 in a large area of East Asian and West European forests due to a faster growth in N deposition than P. Our results suggest a significant contribution of anthropogenic P deposition to C storage, and additional sources of N are needed to support C storage by P in some Asian tropical forests where the deposition rate increased even faster for P than for N. (authors)
Journal
Global Change Biology (Print); ISSN 1354-1013; ; v. 23(no.11); p. 4854-4872
; v. 23(no.11); p. 4854-4872
[en] Water use efficiency (WUE), defined as the ratio of gross primary productivity and evapotranspiration at the ecosystem scale, is a critical variable linking the carbon and water cycles. Incorporating a dependency on vapor pressure deficit, apparent underlying WUE (uWUE) provides a better indicator of how terrestrial ecosystems respond to environmental changes than other WUE formulations. Here we used 20. century simulations from four terrestrial biosphere models to develop a novel variance decomposition method. With this method, we attributed variations in apparent uWUE to both the trend and interannual variation of environmental drivers. The secular increase in atmospheric CO2 explained a clear majority of total variation (6632%: mean one standard deviation), followed by positive trends in nitrogen deposition and climate, as well as a negative trend in land use change. In contrast, interannual variation was mostly driven by interannual climate variability. To analyze the mechanism of the CO2 effect, we partitioned the apparent uWUE into the transpiration ratio (transpiration over evapotranspiration) and potential uWUE. The relative increase in potential uWUE parallels that of CO2, but this direct CO2 effect was offset by 204% by changes in ecosystem structure, that is, leaf area index for different vegetation types. However, the decrease in transpiration due to stomatal closure with rising CO2 was reduced by 84% by an increase in leaf area index, resulting in small changes in the transpiration ratio. CO2 concentration thus plays a dominant role in driving apparent uWUE variations over time, but its role differs for the two constituent components: potential uWUE and transpiration. (authors)
Journal
Global Biogeochemical Cycles; ISSN 0886-6236; ; v. 31(no.11); p. 1639-1655
; v. 31(no.11); p. 1639-1655
[en] This article first reports detections of explosions which occurred on Nord Stream pipelines near Denmark and Sweden, and observations and measurements made, and raises questions about the quantity and methane content of leakages. Then, the authors present the ICOS observation network which aims at tracking the evolution of the main greenhouse gases in the atmosphere, over the ocean and in ecosystems. They report how ICOS has processed information related to these leakages in the Baltic Sea, evokes the development of simulations based on these measurements in order to try to predict evolutions of emissions. They briefly discuss the assessment of methane emission
Journal
[en] Precipitation (PPT) is a primary climatic determinant of plant growth and aboveground net primary production (ANPP) over much of the globe. Thus, PPT-ANPP relationships are important both ecologically and to land-atmosphere models that couple terrestrial vegetation to the global carbon cycle. Empirical PPT-ANPP relationships derived from long-term site-based data are almost always portrayed as linear, but recent evidence has accumulated that is inconsistent with an underlying linear relationship. We review, and then reconcile, these inconsistencies with a nonlinear model that incorporates observed asymmetries in PPT-ANPP relationships. Although data are currently lacking for parameterization, this new model highlights research needs that, when met, will improve our understanding of carbon cycle dynamics, as well as forecasts of ecosystem responses to climate change. (authors)
Journal
New Phytologist; ISSN 0028-646X; ; v. 214(no.1); p. 41-47
; v. 214(no.1); p. 41-47
| 1 | 2 | 3 | Next |