Letteratura scientifica selezionata sul tema "Biogeophysical effects"

Abstract. Afforestation is an important mitigation strategy for climate change due to its carbon sequestration potential. Besides this favorable biogeochemical effect on global CO2 concentrations, afforestation also affects the regional climate by changing the biogeophysical land surface characteristics. In this study, we investigate the effects of an idealized global CO2 reduction to pre-industrial conditions by a Europe-wide afforestation experiment on the regional longwave radiation balance, starting in the year 1986 on a continent entirely covered with grassland. Results show that the impact of biogeophysical processes on the surface temperatures is much stronger than that of biogeochemical processes. Furthermore, biogeophysically induced changes of the surface temperatures, atmospheric temperatures, and moisture concentrations are as important for the regional longwave radiation balance as the global CO2 reduction. While the outgoing longwave radiation is increased in winter, it is reduced in summer. In terms of annual total, a Europe-wide afforestation has a regional warming effect despite reduced CO2 concentrations. Thus, even for an idealized reduction of the global CO2 concentrations to pre-industrial levels, the European climate response to afforestation would still be dominated by its biogeophysical effects.

Abstract. Surface ozone (O3) is an important air pollutant and greenhouse gas. Land use and land cover is one of the critical factors influencing ozone, in addition to anthropogenic emissions and climate. Land use and land cover change (LULCC) can on the one hand affect ozone “biogeochemically”, i.e., via dry deposition and biogenic emissions of volatile organic compounds (VOCs). LULCC can on the other hand alter regional- to large-scale climate through modifying albedo and evapotranspiration, which can lead to changes in surface temperature, hydrometeorology, and atmospheric circulation that can ultimately impact ozone “biogeophysically”. Such biogeophysical effects of LULCC on ozone are largely understudied. This study investigates the individual and combined biogeophysical and biogeochemical effects of LULCC on ozone and explicitly examines the critical pathway for how LULCC impacts ozone pollution. A global coupled atmosphere–chemistry–land model is driven by projected LULCC from the present day (2000) to the future (2050) under RCP4.5 and RCP8.5 scenarios, focusing on the boreal summer. Results reveal that when considering biogeochemical effects only, surface ozone is predicted to have slight changes by up to 2 ppbv maximum in some areas due to LULCC. It is primarily driven by changes in isoprene emission and dry deposition counteracting each other in shaping ozone. In contrast, when considering the combined effect of LULCC, ozone is more substantially altered by up to 5 ppbv over several regions in North America and Europe under RCP4.5, reflecting the importance of biogeophysical effects on ozone changes. In boreal and temperate mixed forests with intensive reforestation, enhanced net radiation and sensible heat induce a cascade of hydrometeorological feedbacks that generate warmer and drier conditions favorable for higher ozone levels. In contrast, reforestation in subtropical broadleaf forests has minimal impacts on boundary-layer meteorology and ozone air quality. Furthermore, significant ozone changes are also found in regions with only modest LULCC, which can only be explained by “remote” biogeophysical effects. A likely mechanism is that reforestation induces a circulation response, leading to reduced moisture transport and ultimately warmer and drier conditions in the surrounding regions with limited LULCC. We conclude that the biogeophysical effects of LULCC are important pathways through which LULCC influences ozone air quality both locally and in remote regions even without significant LULCC. Overlooking the effects of hydrometeorological changes on ozone air quality may cause underestimation of the impacts of LULCC on ozone pollution.

Land-use changes (LUCs) strongly influence regional climates through both the biogeochemical and biogeophysical processes. However, many studies have ignored the biogeophysical processes, which in some cases can offset the biogeochemical impacts. We integrated the field observations, satellite-retrieved data, and a conceptual land surface energy balance model to provide new evidence to fill our knowledge gap concerning how regional warming or cooling is affected by the three main types of LUCs (afforestation, cropland expansion, and urbanization) in different climate zones of China. According to our analyses, similar LUCs presented varied, even reverse, biogeophysical forcing on local temperatures across different climate regimes. Afforestation in arid and semiarid regions has caused increased net radiation that has typically outweighed increased latent evapotranspiration, thus warming has been the net biogeophysical effect. However, it has resulted in cooling in subtropical zones because the increase in net radiation has been exceeded by the increase in latent evapotranspiration. Cropland expansion has decreased the net radiation more than latent evapotranspiration, which has resulted in biogeophysical cooling in arid and semiarid regions. Conversely, it has caused warming in subtropical zones as a result of increases in net radiation and decreases in latent evapotranspiration. In all climatic regions, the net biogeophysical effects of urbanization have generally resulted in more or less warming because urbanization has led to smaller net radiation decreases than latent evapotranspiration. This study reinforces the need to adjust land-use policies to consider biogeophysical effects across different climate regimes and to adapt to and mitigate climate change.

Abstract Future land cover will have a significant impact on climate and is strongly influenced by the extent of agricultural land use. Differing assumptions of crop yield increase and carbon pricing mitigation strategies affect projected expansion of agricultural land in future scenarios. In the representative concentration pathway 4.5 (RCP4.5) from phase 5 of the Coupled Model Intercomparison Project (CMIP5), the carbon effects of these land cover changes are included, although the biogeophysical effects are not. The afforestation in RCP4.5 has important biogeophysical impacts on climate, in addition to the land carbon changes, which are directly related to the assumption of crop yield increase and the universal carbon tax. To investigate the biogeophysical climatic impact of combinations of agricultural crop yield increases and carbon pricing mitigation, five scenarios of land-use change based on RCP4.5 are used as inputs to an earth system model [Hadley Centre Global Environment Model, version 2–Earth System (HadGEM2-ES)]. In the scenario with the greatest increase in agricultural land (as a result of no increase in crop yield and no climate mitigation) there is a significant −0.49 K worldwide cooling by 2100 compared to a control scenario with no land-use change. Regional cooling is up to −2.2 K annually in northeastern Asia. Including carbon feedbacks from the land-use change gives a small global cooling of −0.067 K. This work shows that there are significant impacts from biogeophysical land-use changes caused by assumptions of crop yield and carbon mitigation, which mean that land carbon is not the whole story. It also elucidates the potential conflict between cooling from biogeophysical climate effects of land-use change and wider environmental aims.

Abstract. The terrestrial biosphere is thought to be a key component in the climatic variability seen in the palaeo-record. It has a direct impact on surface temperature through changes in surface albedo and evapotranspiration (so-called biogeophysical effects) and, in addition, has an important indirect effect through changes in vegetation and soil carbon storage (biogeochemical effects) and hence modulates the concentrations of greenhouse gases in the atmosphere. The biogeochemical and biogeophysical effects generally have opposite signs, meaning that the terrestrial biosphere could potentially have played only a very minor role in the dynamics of the glacial–interglacial cycles of the late Quaternary. Here we use a fully coupled dynamic atmosphere–ocean–vegetation general circulation model (GCM) to generate a set of 62 equilibrium simulations spanning the last 120 kyr. The analysis of these simulations elucidates the relative importance of the biogeophysical versus biogeochemical terrestrial biosphere interactions with climate. We find that the biogeophysical effects of vegetation account for up to an additional −0.91 °C global mean cooling, with regional cooling as large as −5 °C, but with considerable variability across the glacial–interglacial cycle. By comparison, while opposite in sign, our model estimates of the biogeochemical impacts are substantially smaller in magnitude. Offline simulations show a maximum of +0.33 °C warming due to an increase of 25 ppm above our (pre-industrial) baseline atmospheric CO2 mixing ratio. In contrast to shorter (century) timescale projections of future terrestrial biosphere response where direct and indirect responses may at times cancel out, we find that the biogeophysical effects consistently and strongly dominate the biogeochemical effect over the inter-glacial cycle. On average across the period, the terrestrial biosphere has a −0.26 °C effect on temperature, with −0.58 °C at the Last Glacial Maximum. Depending on assumptions made about the destination of terrestrial carbon under ice sheets and where sea level has changed, the average terrestrial biosphere contribution over the last 120 kyr could be as much as −50 °C and −0.83 °C at the Last Glacial Maximum.

Carbon (C) sequestration following afforestation is regarded as economically, politically, and technically feasible for fighting global warming, whereas the afforested area which will contribute more efficiently as sinks for CO2 is still uncertain. To compare the benefits for C sequestration combined with its biogeochemical effects, an earth system model of intermediate complexity, the McGill Paleoclimate Model-2 (MPM-2) is used to identify the biogeophysical effects of regional afforestation on shaping global climate. An increase in forest in China has led to a prominent global warming during summer around 45° N. Conversely, the forest expansion in the USA causes a noticeable increase in global mean annual temperature during winter. Afforestation in the USA and China brings about a decrease in annual mean meridional oceanic heat transport, while the afforestation in low latitudes of the southern hemisphere causes an increase. These local and global impacts suggest that regional tree plantations may produce a differential effect on the Earth's climate, and even exert an opposite effect on the annual mean meridional oceanic heat transport; they imply that its spatial variation of biogeophysical feedbacks needs to be considered when evaluating the benefits of afforestation.

Abstract. Modeling studies have shown the importance of biogeophysical effects of deforestation on local climate conditions but have also highlighted the lack of agreement across different models. Recently, remote-sensing observations have been used to assess the contrast in albedo, evapotranspiration (ET), and land surface temperature (LST) between forest and nearby open land on a global scale. These observations provide an unprecedented opportunity to evaluate the ability of land surface models to simulate the biogeophysical effects of forests. Here, we evaluate the representation of the difference of forest minus open land (i.e., grassland and cropland) in albedo, ET, and LST in the Community Land Model version 4.5 (CLM4.5) using various remote-sensing and in situ data sources. To extract the local sensitivity to land cover, we analyze plant functional type level output from global CLM4.5 simulations, using a model configuration that attributes a separate soil column to each plant functional type. Using the separated soil column configuration, CLM4.5 is able to realistically reproduce the biogeophysical contrast between forest and open land in terms of albedo, daily mean LST, and daily maximum LST, while the effect on daily minimum LST is not well captured by the model. Furthermore, we identify that the ET contrast between forests and open land is underestimated in CLM4.5 compared to observation-based products and even reversed in sign for some regions, even when considering uncertainties in these products. We then show that these biases can be partly alleviated by modifying several model parameters, such as the root distribution, the formulation of plant water uptake, the light limitation of photosynthesis, and the maximum rate of carboxylation. Furthermore, the ET contrast between forest and open land needs to be better constrained by observations to foster convergence amongst different land surface models on the biogeophysical effects of forests. Overall, this study demonstrates the potential of comparing subgrid model output to local observations to improve current land surface models' ability to simulate land cover change effects, which is a promising approach to reduce uncertainties in future assessments of land use impacts on climate.

Abstract. Land cover changes have been proposed to play a significant role, alongside emission reductions, in achieving the temperature goals agreed upon under the Paris Agreement. Such changes carry both global implications, pertaining to the biogeochemical effects of land cover change and thus the global carbon budget, and regional or local implications, pertaining to the biogeophysical effects arising within the immediate area of land cover change. Biogeophysical effects of land cover change are of high relevance to national policy and decision makers, and accounting for them is essential for effective deployment of land cover practices that optimise between global and regional impacts. To this end, Earth system model (ESM) outputs that isolate the biogeophysical responses of climate to land cover changes are key in informing impact assessments and supporting scenario development exercises. However, generating multiple such ESM outputs in a manner that allows comprehensive exploration of all plausible land cover scenarios is computationally untenable. This study proposes a framework to explore in an agile manner the local biogeophysical responses of climate under customised tree cover change scenarios by means of a computationally inexpensive emulator, the Tree cover change clIMate Biophysical responses EmulatoR (TIMBER) v0.1. The emulator is novel in that it solely represents the biogeophysical responses of climate to tree cover changes, and it can be used as either a standalone device or as a supplement to existing climate model emulators that represent the climate responses from greenhouse gas (GHG) or global mean temperature (GMT) forcings. We start off by modelling local minimum, mean, and maximum surface temperature responses to tree cover changes by means of a month- and Earth system model (ESM)-specific generalised additive model (GAM) trained over the whole globe; 2 m air temperature responses are then diagnosed from the modelled minimum and maximum surface temperature responses using observationally derived relationships. Such a two-step procedure accounts for the different physical representations of surface temperature responses to tree cover changes under different ESMs whilst respecting a definition of 2 m air temperature that is more consistent across ESMs and with observational datasets. In exploring new tree cover change scenarios, we employ a parametric bootstrap sampling method to generate multiple possible temperature responses, such that the parametric uncertainty within the GAM is also quantified. The output of the final emulator is demonstrated for the Shared Socioeconomic Pathway (SSP) 1-2.6 and 3-7.0 scenarios. Relevant temperature responses are identified as those displaying a clear signal in relation to their surrounding parametric uncertainty, calculated as the signal-to-noise ratio between the sample set mean and sample set variability. The emulator framework developed in this study thus provides a first step towards bridging the information gap surrounding biogeophysical implications of land cover changes, allowing for smarter land use decision making.

The interactions between changing agricultural land and climate are multi faceted and only partially understood. This thesis looks at interactions between crops and climate from assumptions about parameterisations that underpin crop changes in models; the unintended consequences of policies which affect land cover; and the impacts of deliberate crop changes (e.g. biogeoengineering). Focusing on the biogeophysical effects (from albedo, evapotranspiration etc.) these effects are compared to the biogeochemical effects (from greenhouse gases). There are considerable local and global biogeophysical effects to climate from land-use change, which do not necessarily scale linearly with the amount of landuse change itself. Changing the parameterisation of contributory factors to biogeophysical changes can affect the climate at least as much as deliberate alterations. Similarly, climate forced land cover change effects can be larger than land use forced changes. Increases in crop yield from deliberately altered albedo are small, but the changes to climate via albedo from different assumptions of yield are significant at a global and regional scale. This work emphasises the importance of including biogeophysical interactions in assessments of crop and land cover change in policy decisions, but also that the effects of land use change should not be overestimated, as the net effects are often smaller than the parameter uncertainty.

L'agriculture de conservation (AC) est une des solutions basées sur la nature offrant des perspectives intéressantes en termes de leviers d'atténuation et de stratégies d'adaptation au changement climatique. En Afrique subsaharienne, les études des potentiels d'atténuation des changements climatiques par l'AC se concentrent sur les effets biogéochimiques (stockage C, emissions de GES) tandis que les effets biogéophysiques (effets albédo, flux d'énergie) sont souvent ignorés. Dans ce contexte, il est très pertinent d'approfondir les effets de l'AC sur les contributions biogéophysiques de l'agriculture sur le climat afin d'identifier les potentiels leviers d'atténuation associés aux changements de pratiques et les possibles synergies avec les effets biogéochimiques. Nous avons mené des études de quantification des effets biogéophysiques à travers des mesures d'albédo de surface, de rayonnement thermique, de température de surface, de contenu en eau dans le sol, et de dynamiques de croissance des cultures durant deux années culturales au Zimbabwé sur deux types de sol contrasté : un Lixisol abruptique sableux et clair et un Ferralsol xanthique argileux et sombre. Trois pratiques culturales sont comparées dans cette études : le labour conventionnel (CT, pour Conventional Tillage en anglais), la suppression du labour (NT pour No-Tillage en anglais) et le maintien des résidus en surface (NTM pour No-Tillage with Mulch en anglais). Les résultats ont montré une augmentation d'albédo de surface suite à l'adoption de la pratique du NT comparé au CT quel que soit le type de sol. L'apport des résidus de culture en surface comparé au CT à des effets contrasté suivant les types de sol. En effet, les résidus contribuent à une augmentation de l'albédo de surface sur les sols argileux sombres et contribuent à sa diminution sur les sols sableux clairs. Ces changements d'albédo ont entraîné des forçages radiatifs négatifs associés à un effet refroidissant sur le climat du NT quel que soit le type de sol et des effets contrastés pour le NTM, avec un effet refroidissant sur les sols argileux foncés et un effet réchauffant sur les sols sableux clairs. Nous avons comparé ces forçages radiatifs induits par l'albédo de surface aux effets biogéochimiques du stockage de carbone (C) et des émissions de N2O induits par ces mêmes pratiques. Les résultats obtenus ont montré que sur 30 ans de pratique d'AC, les changements d'albédo liés aux pratiques NT et NTM ont des effets climatiques allant de -1,27 à +1,15 t CO2-éq ha⁻¹ an⁻¹, comparables au potentiel de stockage de carbone dans les sols en Afrique subsaharienne. Sur les sols argileux sombres, ces pratiques renforcent l'effet de refroidissement, tandis que sur les sols sableux clairs, elles entraînent un effet réchauffant à court terme, annulant les bénéfices climatiques du C stocké à long terme. Pour mieux comprendre les déterminants des dynamiques d'albédo et être en capacité à les simuler en fonction des pratiques, le modèle STICS a été utilisé, révélant des limites dans la prise en compte de l'effet des tissus sénescents et de l'humidité de surface sur les dynamiques de l'albédo de surface. De nouveaux formalismes ont ensuite été proposés et testés, ce qui a permis d'améliorer les simulations de l'albédo de surface. Cette étude met en avant l'importance d'intégrer les effets biogéophysiques et biogéochimiques pour mieux évaluer les impacts climatiques des pratiques agricoles et optimiser les mesures d'adaptation et d'atténuation
In Sub-Saharan Africa, studies of potential climate change mitigation levers by CA focus more on biogeochemical effects (C storage, GHG emissions) while biogeophysical effects (albedo effects, energy fluxes) are often ignored. In this context, it is very relevant to delve into the effects of CA on agriculture's biogeophysical contributions to climate in order to identify potential mitigation levers associated with changes in practices and possible synergies with the biogeochemical effects. We conducted studies to quantify the biogeophysical effects through measurements of surface albedo, heat radiation, surface temperature, water content in soil, and dynamics of crop growth during two growing years in Zimbabwe on two types of contrasting soil: a sandy, light-coloured abruptic Lixisol and a clayey, dark-coloured xanthic Ferralsol. Three cropping practices are compared in this study: conventional tillage (CT), no-tillage (NT) and no-tillage with mulch (NTM). The results showed an increase in surface albedo following the adoption of NT practice compared to CT regardless of soil type. The contribution of crop residues to surface compared with CT lead to contrasting effects according to soil types. Indeed, the residues contribute to an increase in surface albedo on dark clay soils and contribute to its decrease on light sandy soils. These albedo changes have led to negative radiative forcing associated with a cooling climatic effect on the NT regardless of soil type and contrasting effects for the NTM, with a cooling effect on dark clay soils and a warming effect on light sandy soils. We compared these surface albedo-induced radiative forcings with the biogeochemical effects of carbon (C) storage and N2O emissions induced by these same practices. The results obtained showed that over 30 years of CA practice, albedo changes related to NT and NTM practices have climatic effects ranging from -1.27 to +1.15 t CO2-eq ha-1 year-1, comparable to the potential for carbon storage in soils in Sub-Saharan Africa. On dark clay soils, these practices enhance the cooling effect, while on light sandy soils, they cause a warming effect in the short term, negating the climate benefits of long-term stored C. To better understand the determinants of albedo dynamics and to be able to simulate them according to practices, the STICS model was used, revealing limitations in the consideration of the effect of senescent tissues and surface moisture on the dynamics of surface albedo. New formalisms were then proposed and tested, which allowed to improve the simulations of the surface albedo. This study highlights the importance of integrating biogeophysical and biogeochemical effects to better assess climate impacts of agricultural practices and optimize adaptation and mitigation measures

Uranium contamination of the subsurface remains a significant problem at the Department of Energy Hanford site. A series of column experiments were conducted on Hanford sediment saturated with simulated groundwater to study the effects of aqueous bicarbonate and microbial growth on the mobility of Uranium. Spectral induced polarization (SIP) measurements in the columns were conducted concurrently with pore water sampling in order to monitor changes occurring inside the sediment after the initiation of microbial growth induced by glucose injection. The microbial growth caused significant increases in the real component of the complex conductivity and is the result of ion release into the pore fluid. In addition, an increase in the imaginary conductivity was observed at low frequencies (Hz), which may be due to biotic processes. Due to the use of natural sediment, the SIP response is complex and difficult to understand. However, results across all columns with microbial growth are consistent. Pore water testing showed that microbial growth leads to sudden increases in uranium concentrations; however, microbes also eventually create reducing conditions in the sediment which transforms soluble U6+ to insoluble U4+. Bicarbonate leads to significant increases in uranium concentrations likely due to the formation of mobile uranyl carbonate complexes. For the purposes of field scale remediation, microbial growth in an oxic environment should be avoided. However, within reducing conditions present in the deep vadose zone and phreatic zone, microbial growth seems unlikely to significantly increase uranium mobility.

The Multi-angle Imaging SpectroRadiometer (MISR) experiment is an Instrument Investigation selected for flight aboard the first NASA Earth Observing System polar platform, Eos-A. The purpose of the MISR investigation is to study the effects of geophysical processes and human activities on the Earth’s ecology and climate. Scientific objectives include study of the climatic and environmental impacts of atmospheric aerosols, characterization of heterogeneous cloud fields and their impact on the shortwave radiation budget, and investigation of biosphere-atmosphere interactions and ecosystem change. A detailed understanding of the causes and effects of regional and global change will require long-term monitoring of the Earth system. MISR is a unique component of the Eos instrument suite in that it will systematically acquire multispectral images of the angular reflectance signatures of terrestrial scenes. Theoretical simulations, ground-based measurements, and remotely-sensed observations of aerosol-laden atmospheres, cloud fields, and vegetated landscapes demonstrate the necessity of multi-angle data for climatological and biogeophysical studies. While the spectral coverage and resolution of nadir-viewing imaging spectrometers provide invaluable information on chemical composition, the angular variation of reflectance furnishes the means of inferring physical quantities related to geometric and optical structure, radiative energy transfer, and biosphere-atmosphere mass exchange.