512 research outputs found
Future challenges of representing land-processes in studies on land-atmosphere interactions
Over recent years, it has become increasingly apparent
that climate change and air pollution need to be considered
jointly for improved attribution and projections of
human-caused changes in the Earth system. Exchange processes
at the land surface come into play in this context, because
many compounds that either act as greenhouse gases,
as pollutant precursors, or both, have not only anthropogenic
but also terrestrial sources and sinks. And since the fluxes
of multiple gases and particulate matter between the terrestrial
biota and the atmosphere are directly or indirectly coupled
to vegetation and soil carbon, nutrient and water balances,
quantification of their geographic patterns or changes
over time requires due consideration of the underlying biological
processes. In this review we highlight a number of
critical aspects and recent progress in this respect, identifying
in particular a number of areas where studies have shown
that accounting for ecological process understanding can alter
global model projections of land-atmosphere interactions
substantially. Specifically, this concerns the improved quantification
of uncertainties and dynamic system responses, including
acclimation, and the incorporation of exchange processes
that so far have been missing from global models
even though they are proposed to be of relevance for our understanding
of terrestrial biota-climate feedbacks. Progress
has also been made regarding studies on the impacts of land
use/land cover change on climate change, but the absence of
a mechanistically based representation of human responseprocesses
in ecosystem models that are coupled to climate models limits our ability to analyse how climate change or
air pollution in turn might affect human land use. A more integrated
perspective is necessary and should become an active
area of research that bridges the socio-economic and biophysical
communities
Implications of incorporating N cycling and N limitations on primary production in an individual-based dynamic vegetation model
The LPJ-GUESS dynamic vegetation model uniquely combines an individual- and
patch-based representation of vegetation dynamics with ecosystem
biogeochemical cycling from regional to global scales. We present an updated
version that includes plant and soil N dynamics, analysing the implications
of accounting for CâN interactions on predictions and performance of the
model. Stand structural dynamics and allometric scaling of tree growth
suggested by global databases of forest stand structure and development were
well reproduced by the model in comparison to an earlier multi-model study.
Accounting for N cycle dynamics improved the goodness of fit for broadleaved
forests. N limitation associated with low N-mineralisation rates reduces
productivity of cold-climate and dry-climate ecosystems relative to mesic
temperate and tropical ecosystems. In a model experiment emulating free-air
CO<sub>2</sub> enrichment (FACE) treatment for forests globally, N limitation
associated with low N-mineralisation rates of colder soils reduces CO<sub>2</sub>
enhancement of net primary production (NPP) for boreal forests, while some
temperate and tropical forests exhibit increased NPP enhancement. Under a
business-as-usual future climate and emissions scenario, ecosystem C storage
globally was projected to increase by ca. 10%; additional N requirements
to match this increasing ecosystem C were within the high N supply limit
estimated on stoichiometric grounds in an earlier study. Our results
highlight the importance of accounting for CâN interactions in studies of
global terrestrial N cycling, and as a basis for understanding mechanisms on
local scales and in different regional contexts
Can a âstate of the artâ chemistry transport model simulate Amazonian tropospheric chemistry?
We present an evaluation of a nested high-resolution Goddard Earth Observing System (GEOS)-Chem chemistry transport model simulation of tropospheric chemistry over tropical South America. The model has been constrained with two isoprene emission inventories: (1) the canopy-scale Model of Emissions of Gases and Aerosols from Nature (MEGAN) and (2) a leaf-scale algorithm coupled to the Lund-Potsdam-Jena General Ecosystem Simulator (LPJ-GUESS) dynamic vegetation model, and the model has been run using two different chemical mechanisms that contain alternative treatments of isoprene photo-oxidation. Large differences of up to 100 Tg C yr^(â1) exist between the isoprene emissions predicted by each inventory, with MEGAN emissions generally higher. Based on our simulations we estimate that tropical South America (30â85°W, 14°Nâ25°S) contributes about 15â35% of total global isoprene emissions. We have quantified the model sensitivity to changes in isoprene emissions, chemistry, boundary layer mixing, and soil NO_x emissions using ground-based and airborne observations. We find GEOS-Chem has difficulty reproducing several observed chemical species; typically hydroxyl concentrations are underestimated, whilst mixing ratios of isoprene and its oxidation products are overestimated. The magnitude of model formaldehyde (HCHO) columns are most sensitive to the choice of chemical mechanism and isoprene emission inventory. We find GEOS-Chem exhibits a significant positive bias (10â100%) when compared with HCHO columns from the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) and Ozone Monitoring Instrument (OMI) for the study year 2006. Simulations that use the more detailed chemical mechanism and/or lowest isoprene emissions provide the best agreement to the satellite data, since they result in lower-HCHO columns
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Climate analogues suggest limited potential for intensification of production on current croplands under climate change
Modeling symbiotic biological nitrogen fixation in grain legumes globally with LPJ-GUESS (v4.0, r10285)
Biological nitrogen fixation (BNF) from grain legumes is of significant importance in global agricultural ecosystems. Crops with BNF capability are expected to support the need to increase food production while reducing nitrogen (N) fertilizer input for agricultural sustainability, but quantification of N fixing rates and BNF crop yields remains inadequate on a global scale. Here we incorporate two legume crops (soybean and faba bean) with BNF into a dynamic vegetation model LPJ-GUESS (LundâPotsdamâJena General Ecosystem Simulator). The performance of this new implementation is evaluated against observations from a range of water and N management trials. LPJ-GUESS generally captures the observed response to these management practices for legume biomass production, soil N uptake, and N fixation, despite some deviations from observations in some cases. Globally, simulated BNF is dominated by soil moisture and temperature, as well as N fertilizer addition. Annual inputs through BNF are modeled to be 11.6±2.2âTgâN for soybean and 5.6±1.0âTgâN for all pulses, with a total fixation of 17.2±2.9âTgâNâyr for all grain legumes during the period 1981â2016 on a global scale. Our estimates show good agreement with some previous statistical estimates but are relatively high compared to some estimates for pulses. This study highlights the importance of accounting for legume N fixation process when modeling CâN interactions in agricultural ecosystems, particularly when it comes to accounting for the combined effects of climate and land-use change on the global terrestrial N cycle
Making protected areas effective for biodiversity, climate and food
The spatial extent of marine and terrestrial protected areas (PAs) was among the most intensely debated issues prior to the decision about the post-2020 Global Biodiversity Framework (GBF) of the Convention on Biological Diversity. Positive impacts of PAs on habitats, species diversity and abundance are well documented. Yet, biodiversity loss continues unabated despite efforts to protect 17% of land and 10% of the oceans by 2020. This casts doubt on whether extending PAs to 30%, the agreed target in the Kunming-Montreal GBF, will indeed achieve meaningful biodiversity benefits. Critically, the focus on area coverage obscures the importance of PA effectiveness and overlooks concerns about the impact of PAs on other sustainability objectives. We propose a simple means of assessing and visualising the complex relationships between PA area coverage and effectiveness and their effects on biodiversity conservation, nature-based climate mitigation and food production. Our analysis illustrates how achieving a 30% PA global target could be beneficial for biodiversity and climate. It also highlights important caveats: (i) achieving lofty area coverage objectives alone will be of little benefit without concomitant improvements in effectiveness, (ii) trade-offs with food production particularly for high levels of coverage and effectiveness are likely and (iii) important differences in terrestrial and marine systems need to be recognized when setting and implementing PA targets. The CBD's call for a significant increase in PA will need to be accompanied by clear PA effectiveness goals to reduce and revert dangerous anthropogenic impacts on socio-ecological systems and biodiversity
Climate analogues suggest limited potential for intensification of production on current croplands under climate change
Climate change could pose a major challenge to efforts towards strongly increase food production over the coming decades. However, model simulations of future climate-impacts on crop yields differ substantially in the magnitude and even direction of the projected change. Combining observations of current maximum-attainable yield with climate analogues, we provide a complementary method of assessing the effect of climate change on crop yields. Strong reductions in attainable yields of major cereal crops are found across a large fraction of current cropland by 2050. These areas are vulnerable to climate change and have greatly reduced opportunity for agricultural intensification. However, the total land area, including regions not currently used for crops, climatically suitable for high attainable yields of maize, wheat and rice is similar by 2050 to the present-day. Large shifts in land-use patterns and crop choice will likely be necessary to sustain production growth rates and keep pace with demand
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