iLEAPS Top10 Science highlights

iLEAPS scientific highlights

1. Climate extremes can negate the expected increase in terrestrial carbon uptake
Markus Reichstein, Michael Bahn, Philippe Ciais, Dorothea Frank, Miguel D. Mahecha, Sonia I. Seneviratne, Jakob Zscheischler, Christian Beer, Nina Buchmann, David C. Frank, Dario Papale, Anja Rammig, Pete Smith, Kirsten Thonicke, Marijn van der Velde, Sara Vicca, Ariane Walz & Martin Wattenbach
Climate extremes and the carbon cycle, Nature 500, 287-295, 2013
Evidence is mounting that climate extremes such as droughts or storms can lead to a decrease in regional ecosystem carbon stocks and therefore have the potential to negate an expected, warming-related increase in terrestrial carbon uptake. Extreme events not only affect the carbon cycle concurrently (for example, by reducing vegetation productivity or destroying carbon stocks during fire events) but can initiate significant lagged responses, for instance, changing soil physical and chemical properties and soil respiration; tree mortality after failing hydraulic transport as a result of drought-derived embolism in tree stems; and weakened resistance to abiotic stress; all these can lead to shifts in plant, microbial and animal species composition. Thus, even a small shift in the frequency or severity of climate extremes could substantially reduce carbon sinks and may result in sizeable positive feedbacks to climate warming. Furthermore, lagged effects in societal and economic systems are possible with substantial lagged responses in the carbon cycle, for example if increasing food prices caused by low yields, combined with risk of wind throw, were to encourage conversion of forests to croplands or grasslands. To obtain reliable estimates of the sign and magnitude of future carbon-cycle feedbacks, we need a better understanding and descriptions of both the occurrence of climate extremes themselves and the ecosystem carbon-cycle processes that are triggered by climate extremes. To this end, we advocate a new generation of ecosystem manipulation experiments dedicated to studying extreme events, targeted long-term carbon-cycle observations, and an emphasis on high-resolution climate and biosphere modelling.

2. Observations of increased tropical rainfall preceded by air passage over forests 
D. V. Spracklen, S. R. Arnold and C. M. Taylor
Nature 489, 282–285, (2012), doi:10.1038/nature11390
In a new Nature publication, Spracklen et al. used satellite remote-sensing data of tropical precipitation and vegetation combined with simulated atmospheric transport patterns to assess whether forests actually have an influence on tropical rainfall. They found that for more than 60 per cent of the tropical land surface, air that had passed over extensive vegetation in the preceding few days produced at least twice as much rain as air that has passed over little vegetation. The authors demonstrated that this empirical correlation was consistent with evapotranspiration from the forested areas and estimated that deforestation in the Amazon will lead to reductions of 12 and 21 per cent in wet-season and dry-season precipitation, respectively, 2050.

3. New connections between soil and atmosphere
Kulmala M and Petäjä T
Soil nitrites influence atmospheric chemistry, Science, 333, 1586-1587 (2011), doi:10.1126/science.1211872.
Public discussion of climate change typically revolves around greenhouse gases, aerosol particles, and the role of human actions, but it is just beginning to reflect an awareness of the important role played by the global nitrogen cycle. Emission of HONO from the soil is a good example of how soil processes are linked with atmospheric chemistry (Fig. 6): it is also an example of how trace amounts of reactive nitrogen link the nitrogen and sulfur cycles with the water and carbon cycles. We need to document all the ecosystem-atmosphere cycles including the soil, atmospheric oxidation, and aerosol particles and their links and feedback loops to fully understand how the biosphere affects the atmosphere and the global climate. In order to do this, we need both extensive global modelling and continuous, comprehensive field measurements.

4. Increase in forest water-use efficiency as atmospheric carbon dioxide concentrations rise
Trevor F. Keenan, David Y. Hollinger, Gil Bohrer, Danilo Dragoni, J. William Munger, Hans Peter Schmid & Andrew D. Richardson
Nature 499, 324–327 (2013) doi:10.1038/nature12291
Terrestrial plants remove CO2 from the atmosphere through photosynthesis, a process that is accompanied by the loss of water vapour from leaves. The ratio of water loss to carbon gain, or water-use efficiency, is a key characteristic of ecosystem function that is central to the global cycles of water, energy and carbon. Here we analyse direct, long-term measurements of whole-ecosystem carbon and water exchange. We find a substantial increase in water-use efficiency in temperate and boreal forests of the Northern Hemisphere over the past two decades. We systematically assess various competing hypotheses to explain this trend, and find that the observed increase is most consistent with a strong CO2 fertilization effect. The results suggest a partial closure of stomata —small pores on the leaf surface that regulate gas exchange—to maintain a near-constant concentration of CO2 inside the leaf even under continually increasing atmospheric CO2 levels. The observed increase in forest water-use efficiency is larger than that predicted by existing theory and 13 terrestrial biosphere models. The increase is associated with trends of increasing ecosystem-level photosynthesis and net carbon uptake, and decreasing evapotranspiration. Our findings suggest a shift in the carbon- and water-based economics of terrestrial vegetation, which may require a reassessment of the role of stomatal control in regulating interactions between forests and climate change, and a re-evaluation of coupled vegetation–climate models.

5. Break down boundaries in climate research
Paulo Artaxo
Nature 481, 239 (2012) doi:10.1038/481239a
Scientists wanting to implement change must collaborate between disciplines in natural sciences and in social sciences as well. The ambitious Amazon study LBA (Large Scale Biosphere-Atmosphere Experiment in Amazonia) has been a prime example of this approach for the past two decades. Its success has led to calls for similar projects to be set up to monitor other tropical forests, including those in Africa and southeast Asia. Perhaps most fundamentally, the project encouraged cooperation between physicists, chemists, meteorologists and biologists, to tease apart the Amazon's interwoven scientific strands. Unusually for the time, also economists and social scientists were brought into the research. This was necessary in order to fully understand all the factors influencing such a complex system. Other key factors behind this succesful project have been international cooperation and open data sharing policy.

6. iLEAPS: Integrated land ecosystem - atmosphere processes study (iLEAPS) assessment of global observational networks
A. Guenther, M. Kulmala, A. Turnipseed, J. Rinne, T. Suni, and A. Reissell
Boreal Env Research 16 (2011), 321-336
Long-term, continuous observations are necessary for Earth system investigations and evaluation of simulations. The atmospheric and ecological communities have independently established field sites that have been running for many decades and are integrated into global networks. In the past decade, the importance of long-term observational network focused on land ecosystem - atmosphere exchange, and the processes controlling land-atmosphere coupling, have been increasingly recognised and have led to the building of a global network of water, carbon, and energy flux sites. This is an important step but further enhancements are necessary in order to quantify all of the land-atmosphere processes that need to be included in Earth system models. We describe the current land ecosystem - atmosphere measurement capabilities and present the status and needs for global observational networks.

7. Review:  Forests and climate change: forcings, feedbacks, and the climate benefits of forests
Gordon B. Bonan
Science 320 (2008), 1444-1449 DOI: 10.1126/science.1155121
The world's forests influence climate through physical, chemical, and biological processes that affect planetary energetics, the hydrologic cycle, and atmospheric composition. These complex and nonlinear forest-atmosphere interactions can dampen or amplify anthropogenic climate change. Tropical, temperate, and boreal reforestation and afforestation attenuate global warming through carbon sequestration. Biogeophysical feedbacks can enhance or diminish this negative climate forcing. Tropical forests mitigate warming through evaporative cooling, but the low albedo of boreal forests is a positive climate forcing. The evaporative effect of temperate forests is unclear. The net climate forcing from these and other processes is not known. Forests are under tremendous pressure from global change. Interdisciplinary science that integrates knowledge of the many interacting climate services of forests with the impacts of global change is necessary to identify and understand as yet unexplored feedbacks in the Earth system and the potential of forests to mitigate climate change.

8. iLEAPS/LULCC: Importance of background climate in determining impact of land-cover change on regional climate 
A. J. Pitman, F. B. Avila, G. Abramowitz, Y. P. Wang, S. J. Phipps1 & N. de Noblet-Ducoudré
Nature Climate Change 1, 472–475 (2011) DOI: doi:10.1038/nclimate1294
Humans have modified the Earth's climate through emissions of greenhouse gases and through land-use and land-cover change (LULCC). Increasing concentrations of greenhouse gases in the atmosphere warm the mid-latitudes more than the tropics, in part owing to a reduced snow–albedo feedback as snow cover decreases. Higher concentration of carbon dioxide also increases precipitation in many regions as a result of an intensification of the hydrological cycle. The biophysical effects of LULCC since pre-industrial times have probably cooled temperate and boreal regions and warmed some tropical regions. Here we use a climate model to show that how snow and rainfall change under increased greenhouse gases dominates how LULCC affects regional temperature. Increased greenhouse-gas-driven changes in snow and rainfall affect the snow–albedo feedback and the supply of water, which in turn limits evaporation. These changes largely control the net impact of LULCC on regional climate. Our results show that capturing whether future biophysical changes due to LULCC warm or cool a specific region therefore requires an accurate simulation of changes in snow cover and rainfall geographically coincident with regions of LULCC. This is a challenge to current climate models, but also provides potential for further improving detection and attribution methods.

9. Indirect radiative forcing of climate change through ozone effects on the land-carbon sink.
Sitch S, Cox PM, Collins WJ, and Huntingford C (2007). 
Nature 448, 791-794, doi:10.1038/nature06059
Tropospheric ozone is known to damage plants, reducing plant primary productivity and crop yields, yet increasing atmospheric carbon dioxide concentrations are thought to stimulate plant primary productivity.Increased carbon dioxide and ozone levels can both lead to stomatal closure, which reduces the uptake of either gas, and in turn limits the damaging effect of ozone and the carbon dioxide fertilization of photosynthesis. Here, we estimated the impact of projected changes in ozone levels on the land-carbon sink, using a global land carbon cycle model modified to include the effect of ozone deposition on photosynthesis and to account for interactions between ozone and carbon dioxide through stomatal closure. We found a significant suppression of the global land-carbon sink as increases in ozone concentrations affect plant productivity. In consequence, more carbon dioxide accumulates in the atmosphere. We suggest that the resulting indirect radiative forcing byozone effects on plants could contribute more to global warming than the direct radiative forcing due to tropospheric ozone increases.

10. Untangling aerosol effects on clouds and precipitation in a buffered system 
Bjorn Stevens and Graham Feingold
Nature (Vol 461, Issue 7264 , p. 607, 2009)
It is thought that changes in the concentration of cloud-active aerosol can alter the precipitation efficiency of clouds, thereby changing cloud amount and, hence, the radiative forcing of the climate system. Despite decades of research, it has proved frustratingly difficult to establish climatically meaningful relationships among the aerosol, clouds and precipitation. As a result, the climatic effect of the aerosol remains controversial. We propose that the difficulty in untangling relationships among the aerosol, clouds and precipitation reflects the inadequacy of existing tools and methodologies and a failure to account for processes that buffer cloud and precipitation responses to aerosol perturbations.


Other top iLEAPS highlights

Ecosystem photosynthesis inferred from measurements of carbonyl sulphide flux
David Asaf, Eyal Rotenberg, Fyodor Tatarinov, Uri Dicken, Stephen A. Montzka and Dan Yakir
Nature Geoscience 6, 186–190 (2013) doi:10.1038/ngeo1730 
Limited understanding of carbon dioxide sinks and sources on land is often linked to the inability to distinguish between the carbon dioxide taken up by photosynthesis, and that released by respiration. Carbonyl sulphide, a sulphur-containing analogue of carbon dioxide, is also taken up by plants but not released, and could potentially serve as a powerful proxy for photosynthetic carbon dioxide uptake, which cannot be directly measured above the leaf scale. Indeed, variations in atmospheric concentrations of carbonyl sulphide are closely related to those of carbon dioxide at regional, local and leaf scales. We used eddy covariance and laser spectroscopy to estimate the net exchange of carbon dioxide and carbonyl sulphide across three pine forests, a cotton field and a wheat field in Israel. We estimated gross primary productivity—a measure of ecosystem photosynthesis—directly from the carbonyl sulphide fluxes, and indirectly from carbon dioxide fluxes. The two estimates agreed within an error of +/- 15%. The ratio of carbonyl sulphide to carbon dioxide flux at the ecosystem scale was consistent with the variability in mixing ratios observed on seasonal timescales in the background atmosphere. We suggest that atmospheric measurements of carbonyl sulphide flux could provide an independent constraint on estimates of gross primary productivity, key to projecting the response of the land biosphere to climate change.

The Amazon basin in transition
E. Davidson, A. de Araujo, P. Artaxo, J. Balch, I. Brown, M. Bustamante, M. Coe, R. DeFries, M. Keller, M. Longo, J.W. Munger, W. Schroeder, B.S. Soares-Filho, C. Souza Jr & S. Wofsy
Nature 481, 321-328 (2012) doi:10.1038/nature10717
Agricultural expansion and climate variability have become important agents of disturbance in the Amazon basin.  Recent studies have demonstrated considerable resilience of Amazonian forests to moderate annual drought, but they also show that interactions between deforestation, fire and drought potentially lead to losses of carbon storage and changes in regional precipitation patterns and river discharge. Although the basin-wide impacts of land use and drought may not yet surpass the magnitude of natural variability of hydrologic and biogeochemical cycles, there are some signs of a transition to a disturbance-dominated regime. These signs include changing energy and water cycles in the southern and eastern portions of the Amazon basin.

Contribution of Semi-Arid Forests to the Climate System
Eyal Rotenberg and Dan Yakir
Science 327, 451 (2010); doi: 10.1126/science.1179998
Forests both take up CO2 and enhance absorption of solar radiation, with contrasting effects on global temperature. Based on a9-year study in the forests’ dry timberline, we show that substantial carbon sequestration (cooling effect) is maintained in the large dry transition zone (precipitation from 200 to 600 millimeters) by shifts in peak photosynthetic activities from summer to early spring, and this is counteracted by longwave radiation (L) suppression (warming effect), doubling the forestation shortwave (S) albedo effect. Several decades of carbon accumulation are required to balance the twofold S + L effect. Desertification over the past several decades, however, contributed negative forcing at Earth’s surface equivalent to ~20% of the global anthropogenic CO2 effect over the same period, moderating warming trends.

Combined climate and carbon-cycle effects of large-scale deforestation.
Bala G, Caldeira K, Wickett M, Phillips TJ, Lobell DB, Delire C, and Mirin A (2007) 
PNAS 104:16, doi10.1073/pnas.0608998104
The prevention of deforestation and promotion of afforestation have often been cited as strategies to slow global warming. Deforestation releases CO2 to the atmosphere, which exerts a warming influence on Earth's climate. However, biophysical effects of deforestation, which include changes in land surface albedo, evapotranspiration, and cloud coveralso affect climate. Here we present results from several large-scale deforestation experiments performed with a three-dimensional coupled globalcarbon-cycle and climate model. These simulations were performed by using afully three-dimensional model representing physical and biogeochemical interactions among land, atmosphere, and ocean. We find that global-scale deforestation has a net cooling influence on Earth's climate, because the warming carbon-cycle effects of deforestation are overwhelmed by the net cooling associated with changes in albedo and evapotranspiration. Latitude-specific deforestation experiments indicate that afforestation projects in the tropics would be clearly beneficial in mitigating global-scale warming, but would be counterproductive if implemented at high latitudes and would offer only marginal benefits in temperate regions. Although these results question the efficacy of mid- and high-latitude afforestation projects for climate mitigation, forests remain environmentally valuable resources for many reasons unrelated to climate.

iLEAPS/Taita research station: Driving forces of agricultural expansion and future land-use scenarios in Kenya’s biodiversity hotspot 
Modelling agricultural expansion in Kenya’s Eastern Arc Mountains biodiversity hotspot
Eduardo Eiji Maeda *, Barnaby J.F. Clark, Petri Pellikka, Mika Siljander
Agricultural Systems 103 (2010) 609–620
The Taita Hills are the northernmost part of the Eastern Arc Mountains of Kenya and Tanzania, which is one of the most important regions for biological conservation in the world. The indigenous cloud forests in this area have suffered substantial degradation for several centuries due to agricultural expansion. In the Taita Hills, currently only 1% of the original forested area remains preserved. In order to create effective policies to preserve the natural resources and biodiversity of the Eastern Arc Mountains, it is crucial to understand the causes and interactions involved in the landscape changes in the most degraded areas. The research presented here aimed to understand the role of landscape attributes and infrastructure components as driving forces of agricultural expansion in the Taita Hills. Geospatial technology tools and a landscape dynamic simulation model were integrated to identify and evaluate the driving forces of agricultural expansion and simulate future landscape scenarios. The results indicate that, if current trends persist, agricultural areas will occupy roughly 60% of the study area by 2030. Agricultural expansion will likely take place predominantly in lowlands and foothills throughout the next 20 years, increasing the spatial dependence on distance to rivers and other water bodies. The main factors driving the spatial distribution of new croplands were the distance to markets, proximity to already established agricultural areas and distance to roads. Other driving forces of the agricultural expansion, as well as their implications for natural resources conservation, are discussed. Further studies are necessary to integrate the effects of population pressure and climate change on the sustainability and characteristics of local agricultural systems.

iLEAPS-ESA/ALANIS: On the use of satellites to obtain information on the occurrence of natural and anthropogenic aerosols over the boreal Eurasian forest 
G. de Leeuw, A. Arola, L. Sogacheva, N. Kivekäs, V.-M. Kerminen, A. Arneth, T. Christensen, H. Korhonen, A.-I. Partanen, H. Lappalainen, P. Kolmonen, T. Mielonen, M. Sofiev, M. Kulmala, and S. Pinnock
iLEAPS special issue in Biogeosciences Discuss., 8, 8451-8483, 2011
The ALANIS (Atmosphere-LANd Integrated Study) -Aerosols project is a feasibility study on the use of existing satellite data for discriminating between natural aerosols emitted by boreal Eurasian forests and long-range transported anthropogenic aerosols. We provide an overview of different satellite products which are potentially useful to obtain this kind of information. New particles formed through the secondary production of aerosols from their precursor gases are initially too small to be observed directly with optical instruments used for earth observation (EO). However, we found that through the use of proxies, information can be obtained on global nucleation mode aerosol concentrations. Particles with diameter larger than about 50–100 nm can be observed with EO instruments as well as using several different types of in situ observations. Our examples show the complementarity of different data sources to obtain information on the temporal and spatial information on the nature of aerosols over the boreal forest.

Comparing carbon sequestration in temperate freshwater wetland communities
Blanca Bernal and William J. Mitsch
Global Change Biology 8:5, 1636–1647 (2012)
Many freshwater wetlands are significant carbon sinks; however, most studies focus on boreal peatlands with less attention paid to other climates and wetland types. This study compared six temperate wetland communities in Ohio that belong to two distinct hydrogeomorphic types: 1) an isolated depressional wetland site connected to groundwater and 2) a riverine flow-through wetland site that receives water from an agricultural watershed. The depressional wetland communities sequestered twice as much carbon a year than the riverine communities, and the vegetation types had a significant influence on the results. The study highlights the importance of addressing wetland types and communities in more detail when assessing the role of wetlands as carbon sequestering systems in global carbon budgets.

Conceptual design and quantification of phosphorus flows and balances at the country scale: The case of France
Senthilkumar K, Nesme T, Mollier A, and Pellerin S
Global Biogeochemical Cycles, vol. 26, GB2008, 14 pp. (2012), doi:10.1029/2011GB004102
In order to analyse the influence of current economic and social organizations on global biogeochemical cycles, we took major phosphorus (P) flows in France as a case study and divided France into agriculture, industry, domestic, import and export sectors, identifying a total of 25 internal and eight external P flows that we quantified on a yearly basis for a period of 16 years (from 1990 to2006) in order to understand long-term P flows. The industrial sector remained the largest contributor to P flows in France, followed by the agriculture and domestic sectors. We found that French soil P balance reduced from 18 kg ha-1 in 1990 to 4 kg ha-1 in 2006, mainly because of reduced application of inorganic P fertilizer. The ratio between national soil P input and P in food products was only 10%, and half of the net P import in France was lost to the environment mainly through the landfilling of municipal and industrial waste, disposal of treated wastewater from which P was partially removed, and P losses from agricultural soils though erosion and leaching.

Forestation of boreal peatlands: Impacts of changing albedo and greenhouse gas fluxes on radiative forcing
A. Lohila, K. Minkkinen, J. Laine, I. Savolainen, J.-P. Tuovinen, L. Korhonen, T. Laurila, H. Tietäväinen, and A. Laaksonen.
J. Geophys. Res., 115 (2010), G04011, doi:10.1029/2010JG001327
Pristine peatlands are usually open habitats, with dominating field and bottom‐layer vegetation, and often with sparse tree stands. Peatland drainage (lowering of the water table) is a common management prescription to improve forest growth; as a result, over 10 million ha of peatlands have been drained for forestry in the Nordic countries and Russia. This study compared the effect of changes in albedo and GHG fluxes on the radiative balance of forested peatlands during one forest rotation. The smaller albedo of the forest compared to the peatland led to warming that was very similar in magnitude to the cooling resulting from the increased carbon sequestration of the growing trees, and we found evidence of both net cooling and net warming on different sites. The results thus show that, when assessing the climate effect of a land use change including either forestation or deforestation, it is necessary to take into account not only GHGs, but also, at least as importantly, the effect of a changing albedo.

Ground-based Network of NDVI measurements for tracking temporal dynamics of canopy structure and vegetation phenology in different biomes
K. Soudania, G. Hmiminaa, N. Delpierrea, et al.
Remote Sensing of Environment, 123 (August 2012), pp. 234-245,doi:10.1016/j.rse.2012.03.012
Plant phenology characterises the seasonal cyclicity of biological events such as budburst, flowering, fructification, leaf senescence and leaf fall. The timing of these events is considered as a good indicator of climate change impacts and as a key parameter for understanding and modelling vegetation–climate interactions. Since 2005, a network of forest and herbaceous sites has been equipped with laboratory made NDVI (Normalised Differential Vegetation Index, a proxy for photosynthesis) sensors to monitor the temporal dynamics of canopy structure and phenology at an intra-daily time step. The NDVI sensors were installed on towers, a few metres above the top of the canopy and looking downwards. In this study, we present recent results obtained in several contrasting biomes in France, French Guiana, Belgium and Congo. In addition to its importance for phenological studies, this ground-based Network of NDVI measurement provides data needed for the calibration and direct validation of satellite observations and products.

Historical land use change and associated carbon emissions in Brazil from 1940 to 1995
Costa MH, Silveira Soares-Filho B, de Barros Viana Hissa L, and Cavalcante Leite C
Global Biogeochemical Cycles, 26, GB2011, 13 pp. (2012), doi:10.1029/2011GB004133
Based on a reconstruction of land use patterns 1940-1995 produced by merging satellite imagery with census data, we determined the net emission of carbon from land use change during this period, 17.2 Pg (C). The evaluation of land-use change impacts is in general limited by the knowledge of past land use conditions. Most publications on the field present only a vague description of the earlier patterns of land use, which is usually insufficient for more comprehensive studies.Ours is the first spatially explicit reconstruction of historical land use patterns in Brazil, including both croplands and pasturelands, for the period between 1940 and 1995. Despite international concerns about Amazon deforestation emissions, 72% of Brazil's carbon emissions during the period actually came from deforestation in the Atlantic Forest and Cerrado biomes. Brazil's carbon emissions from land use change are about 11 times larger than its emissions from fossil fuel burning, although only about 18.1% of the native biomass has been lost due to agricultural expansion, which is similar to the global mean (17.7%).

iLEAPS: Bioenergy crop on drained and abandoned cutover peatlands a potent climate mitigation option
Narasinha J. Shurpali, Christina Biasi, Simo Jokinen, Niina Hyvönen, Pertti J. Martikainen
Linking water vapor and CO2 exchange from a perennial bioenergy crop on a drained organic soil in eastern Finland.
Agricultural and Forest Meteorology (2013) 168, 47–58
With the aim of addressing the broader issues of land use, climate change and energy crisis, we initiated eddy covariance measurements of energy and CO2 exchange from a bioenergy crop (reed canary grass, Phalaris arundinaceae, L.) cultivated on a drained organic soil (a cutover peatland) in eastern Finland in the spring of 2004. The climatically diverse dataset from the 2004 to 2010 period allowed us to characterize the interannual variability in water vapor exchange and to understand the linkage between energy and CO2 exchange from this perennial crop during two extreme growing seasons. Interannual variability in ecosystem processes of energy and CO2 exchange were attributed primarily to marked differences in the amount and distribution of seasonal precipitation. Wet years resulted in high bulk surface conductance (gs), high evapotranspiration (ET) and low sensible heat flux with a peak seasonal Bowen ratio (β = 0.1). These conditions were favourable for a high uptake of atmospheric CO2. Dry years, on the contrary, were marked by long dry spells during important phases of crop growth, climatic and soil moisture stress leading to high evaporative demand, low gs values, reduced evapotranspiration and high sensible heat flux (β = 0.3–0.4). On a seasonal basis, the ET losses during a dry year were 13% lower compared to those during a wet year. The corresponding reduction in gross ecosystem productivity (GEP), however, was to the extent of 21%. Owing to the ability of this perennial crop to sequester large amounts of atmospheric carbon into its above- and below-ground biomass, the water use efficiency (defined as the slope of the linear regression of monthly values of GEP against ET) of this cultivation system was found to be 9.1 g CO2 per kg of H2O lost as ET. The results stemming from this work further support our earlier conclusions that this bioenergy system is a suitable land use option on drained and abandoned cutover peatlands with a high potential for offsetting CO2 load to the atmosphere.

Handmade Software, Inc. Image Alchemy v1.13<br />

Monthly sums of gross ecosystem productivity (GEP – in g CO2 month−1 in the upper panel) and evapotranspiration (ET – in mm month−1 in the lower panel) losses from reed canary grass during a wet (columns in black) and dry (open columns) year cultivated on a drained organic soil in eastern Finland.

iLEAPS: First synoptic empirical models of global biosphere-atmosphere exchange
Drawing on meteorological data and observations provided by satellites as well as observations from FLUXNET, Jung et al. produced the first synoptic empirical models of global biosphere-atmosphere carbon, water and sensible heat exchange. FLUXNET, a global network of eddy covariance towers, generates high spatial- and temporal- resolution measurements of wind speed, trace gas fluxes, and other atmospheric parameters. Combining these point measurements with the broad areal coverage of satellite observations, the authors produced a 0.5° by 0.5° spatial resolution set of monthly data that spanned from 1982 to 2008. Using a machine learning approach—a computational technique that sifts through vast data sets to identify underlying patterns—the authors developed a model that accurately estimated a number of ecosystem-atmosphere fluxes, including the amount of carbon used to fuel plant growth, the carbon produced by the ecosystem, and the latent and sensible energy transfer rates. The authors’ model omits a number of known processes and gives up control over how each environmental dynamic is represented in order to generate a model based entirely on observational data. Many new large scale patterns of atmosphere-biosphere exchange have been discovered, such as hotspots of interannual variability and the strong control of the water-cycle on the carbon cycle. Jung et al. suggest that their empirical approach is not meant to replace theoretically-derived simulations, but rather work with them to improve the understanding of environmental dynamics. The global Earth System modeling community is already profiting from this product (e.g. Bonan et al. 2011).
Jung, M., M. Reichstein, H. A. Margolis, A. Cescatti, A. D. Richardson, M. A. Arain, A. Arneth, C. Bernhofer, D. Bonal, J. Chen, D. Gianelle, N. Gobron, G. Kiely, W. Kutsch, G. Lasslop, B. E. Law, A. Lindroth, L. Merbold, L. Montagnani, E. J. Moors, D. Papale, M. Sottocornola, F. Vaccari, and C. Williams. 2011. Global patterns of land-atmosphere fluxes of carbon dioxide, latent heat, and sensible heat derived from eddy covariance, satellite, and meteorological observations. Journal of Geophysical Research - Biogeosciences 116:G00J07, doi:10.1029/2010JG001566.

iLEAPS: Ground-level ozone influenced by circadian control of isoprene emissions
C. N. Hewitt, K. Ashworth, A. Boynard, A. Guenther, B. Langford, A. R. MacKenzie, P. K. Misztal, E. Nemitz, S. M. Owen, M. Possell, T. A. M. Pugh, A. C. Ryan, O. Wild
Nature Geoscience (Vol. 4, 671–674, 2011); doi:10.1038/ngeo1271
The volatile organic compound isoprene is produced by many plant species, and provides protection against biotic and abiotic stresses. Globally, isoprene emissions from plants are estimated to far exceed anthropogenic emissions of volatile organic compounds. Once in the atmosphere, isoprene reacts rapidly with hydroxyl radicals to form peroxy radicals, which can react with nitrogen oxides to form ground-level ozone. We used canopy-scale measurements of isoprene fluxes from two tropical ecosystems in Malaysia—a rainforest and an oil palm plantation—and three models of atmospheric chemistry to explore the effects of isoprene fluxes on ground-level ozone. We showed that isoprene emissions in these ecosystems are under circadian control (biological clock over 24 h) on the canopy scale, particularly in the oil palm plantation. As a result, these ecosystems emit less isoprene than present emissions models predict. Using local-, regional- and global-scale models of atmospheric chemistry and transport, we show that accounting for this circadian control of isoprene emissions brings model predictions of ground-level ozone into better agreement with measurements, especially in isoprene-sensitive regions of the world.

iLEAPS: Long-term experiment reveals contrasting effects of plant diversity, N fertilization, and elevated carbon dioxide on grassland soil N cycling
Kevin E. Mueller, Sarah E. Hobbie, David Tilman, Peter B. Reich (2013)
Effects of plant diversity, N fertilization, and elevated carbon dioxide on grassland soil N cycling in a long-term experiment.
Global Change Biology (accepted), DOI: 10.1111/gcb.12096
The effects of global environmental changes on soil nitrogen (N) pools and fluxes have consequences for ecosystem functions such as plant productivity and N retention. In a 13-year grassland experiment, we evaluated how elevated atmospheric carbon dioxide (CO2), N fertilization, and plant species richness alter soil N cycling. We focused on soil inorganic N pools, including ammonium and nitrate, and two N fluxes, net N mineralization and net nitrification. In contrast with existing hypotheses, such as progressive N limitation, and with observations from other, often shorter, studies, elevated CO2 had relatively static and small, or insignificant, effects on soil inorganic N pools and fluxes. Nitrogen fertilization had inconsistent effects on soil N transformations, but increased soil nitrate and ammonium concentrations. Plant species richness had increasingly positive effects on soil N transformations over time, likely because in diverse subplots the concentrations of N in roots increased over time. Species richness also had increasingly positive effects on concentrations of ammonium in soil, perhaps because more carbon accumulated in soils of diverse subplots, providing exchange sites for ammonium. By contrast, subplots planted with 16 species had lower soil nitrate concentrations than less diverse subplots, especially when fertilized, probably due to greater N uptake capacity of subplots with 16 species. Monocultures of different plant functional types had distinct effects on N transformations and nitrate concentrations, such that not all monocultures differed from diverse subplots in the same manner. The first few years of data would not have adequately forecast the effects of N fertilization and diversity on soil N cycling in later years; therefore, the dearth of long-term manipulations of plant species richness and N inputs is a hindrance to forecasting the state of the soil N cycle and ecosystem functions in extant plant communities.

iLEAPS: Role of land surface processes and diffuse/direct radiation partitioning in simulating the European climate
E. L. Davin and S. I. Seneviratne
Biogeosciences Discuss., 8, 11601-11630, 2011
Land processes and diffuse/direct radiation partitioning has important effects on surface fluxes and associated regional-scale climate feedbacks. Our study showed that using a more advanced land-surface model, the performance of a regional climate model (RCM) improved clearly. This demonstrates the benefit of using a realistic representation of land surface processes for regional climate simulations. Taking into account the variability in diffuse/direct light partitioning at the surface further improves the model performance in terms of summer temperature variability at the monthly and daily time scales. Comparisons with observations show that the RCM realistically captures temporal variations in diffuse/direct light partitioning as well as the evapotranspiration sensitivity to these variations. Our results suggest that a modest but consistent fraction (up to 3%) of the overall variability in summer temperature can be explained by variations in the diffuse to direct ratio.

iLEAPS: Soil Nitrite as a Source of Atmospheric HONO and OH Radicals
H Su, Y Cheng, R Oswald, T Behrendt, I Trebs, FX Meixner, MO Andreae, P Cheng, Y Zhang, and U Pöschl
Science Vol. 333 no. 6049 pp. 1616-1618 DOI: 10.1126/science.1207687
Hydroxyl radicals (OH) are a key species in atmospheric photochemistry. In the lower atmosphere, up to ~30% of the primary OH radical production is attributed to the photolysis of nitrous acid (HONO), and field observations suggest a large missing source of HONO. We show that soil nitrite can release HONO and explain the reported strength and diurnal variation of the missing source. Fertilized soils with low pH appear to be particularly strong sources of HONO and OH. Thus, agricultural activities and land-use changes may strongly influence the oxidizing capacity of the atmosphere. Because of the widespread occurrence of nitrite-producing microbes, the release of HONO from soil may also be important in natural environments, including forests and boreal regions.

iLEAPS: Sum of CH4 and N2O losses an order of magnitude higher than net CO2 uptake in an agriculture-to-poplar transition
D. Zona, I.A. Janssens, M. Aubinet, B. Gioli, S. Vicca, R. Fichot, R. Ceulemans (2012)
Fluxes of the greenhouse gases (CO2, CH4 and N2O) above a short-rotation poplar plantation after conversion from agricultural land.
Agricultural and Forest Meteorology 169 (2013) 100–110.
The increasing demand for renewable energy may lead to the conversion of millions of hectares into bioenergy plantations with a possible substantial transitory carbon (C) loss. In this study we report on the greenhouse gas fluxes (CO2, CH4, and N2O) measured using eddy covariance of a short-rotation bioenergy poplar plantation converted from agricultural fields. During the first six months after the establishment of the plantation (June–December 2010) there were substantial CO2, CH4, and N2O emissions (a total of 5.36 ± 0.52 Mg ha−1 in terms of CO2 equivalents). Nitrous oxide loss mostly occurred during a week-long peak emission after an unusually large rainfall. This week-long N2O emission represented 52% of the entire N2O loss during one and an half years of measurements. As most of the N2O loss occurred in just this week-long period, accurately capturing these emission events are critical to accurate estimates of the GHG balance of bioenergy. While initial establishment (June–December 2010) of the plantation resulted in a net CO2 loss into the atmosphere (2.76 ± 0.16 Mg ha−1), in the second year (2011) there was substantial net CO2 uptake (−3.51 ± 0.56 Mg ha−1). During the entire measurement period, CH4 was a source to the atmosphere (0.63 ± 0.05 Mg (CO2eq) ha−1 in 2010, and 0.49 ± 0.05 Mg (CO2eq) ha−1 in 2011), and was controlled by water table depth. Importantly, over the entire measurement period, the sum of the CH4 and N2O losses was much higher (3.51 ± 0.52 Mg (CO2eq) ha−1) than the net CO2 uptake (−0.76 ± 0.58 Mg ha−1). As water availability was an important control on the GHG emission of the plantation, expected climate change and altered rainfall pattern could increase the negative environmental impacts of bioenergy.

iLEAPS/ABBA: Spatial variations of nitrogen trace gas emissions from tropical mountain forests in Nyungwe, Rwanda
N. Gharahi Ghehi, C. Werner, L. Cizungu Ntaboba, J. J. Mbonigaba Muhinda, E. Van Ranst, K. Butterbach-Bahl, R. Kiese, and P. Boeckx
Biogeosciences Discuss., 8, 11631–11660, 2011
Globally, tropical forest soils represent the second largest source of N2O and NO. However, there is still considerable uncertainty on the spatial variability and soil properties controlling N trace gas emission. To investigate how soil properties affect N2O and NO emission, we carried out an incubation experiment with soils from 31 locations in the Nyungwe tropical mountain forest in southwestern Rwanda. The results suggested both climatic and biological controls over N2O and NO emissions and that chemo-denitrification might, at least for N2O, be an important production pathway.

iLEAPS/AMMA: Anatomy of an observed African easterly wave in July 2006
Bain, C., Parker, D. J., Dixon, N., Fink, A. H., Taylor, C. M., Brooks, B. & Milton, S. F. (2011)
Quarterly Journal of the Royal Meteorological Society, 137. 923–933.
The detailed structure of an African easterly wave (AEW) observed during the AMMA field campaign is analyzed. A complex circulation pattern was observed: the overall structure of convection and the positive vorticity of the trough region had an elongated inverted-V appearance, wrapped around an area of low winds and clear skies. Satellite imagery showed that the AEW was a significant influence on the modulation of convection on the large scale. The wave was identified initially through its strong signature on soil moisture and convection. The AEW structure observed was not anticipated and has not been discussed in previous literature. In addition, wave tracking using a Hovmöller diagram of meridional winds did not detect the wave, and a Hovmöller of vorticity showed the wave moved at a slower speed than other AEWs in July. New schematics explaining the structure are presented, describing the case as observed by satellites and analyzed by a limited-area version of the Met Office Unified Model. Positive vorticity branches of the inverted-V can be regarded as analogous to atmospheric fronts, with characteristic gradients in winds and thermodynamic properties, acting as locations for enhanced convection. The implications of the new case are discussed in relation to previous theory and it is suggested that the accepted model of an idealized AEW is incomplete and should be extended to include more complex structures.

iLEAPS/AMMA: Increasing River Flows in the Sahel?
Amogu O., L. Descroix, K. Souley Yéro, E. Le Breton, I. Mamadou, A. Ali, T. Vischel, J.-C. Bader, I. Bouzou Moussa, E. Gautier, S. Boubkraoui and P. Belleudy (2010)
Water, 2, 170-199; doi:10.3390/w202017
Despite the drought observed since the 1970 in most of the West African Sahel, runoff and rivers discharges have been found to increase in this region. This paper the regional extension of such a phenomenon and demonstrates that the increase in runoff is observed from the point scale up to the regional scale. It highlights the opposition of functioning between a Sahelian zone, where the Sahel’s paradox applies, and the Sudanian and Guinean areas, where runoff has been logically decreasing with the rainfall. The current trend is evidenced using experimental runoff plots and discharge data from the local to the regional scales. This trend may be related to land use change rather than climate change, although trends have also been found in the absence of land use changes (Gardelle et al 2010).

iLEAPS/AMMA: Mineral dust and carbonaceous aerosols in West Africa: source assessment and characterization
Flament P., Deboudt K., Cachier H., Chatenet B. & Mériaux X. (2011)
Atmospheric Environment 45, 3742–3749 
As part of AMMA project, an intensive field was carried out in West Africa during the dry season (February 2006), near M'Bour, Senegal. Major elements (Al, Ca and Fe), total (TC) and black carbon (BC), and water soluble ion (Na+, K+, Mg2+, NH4+, Cl−, NO3−, SO42-, PO43-) concentrations were measured, as well as total mass, number concentration and aethalometer measurements of PM-10. Mineral dust in the surface layer is principally present in the coarse fraction representing 75–90% of the collected mass (wt.%). As suggested by backward trajectories of the air masses and supported by the variations of Ca/Al ratios, dust originates mainly from Northern Sahara. Particulate organic matter (POM) concentrations are more variable, but POM is mainly present in the fine fraction (up to 77 wt.%). Its presence is due to local sources (domestic fires) rather than to remote sources as open-field vegetation fires in the Sahelian zone. Comparisons of BC concentrations measured with an aethalometer in the Ultra-violet and the Near-infrared wavelengths, show that POM originating from the adjacent Western African coast contains less aromatics than POM transported from the main biomass burning areas of the Sahelian zone. Smouldering, the main combustion process for locally emitted carbon aerosols appears to generate less aromatic compounds than burning of vegetation.

iLEAPS/ACPC: Long-term impacts of aerosols on the vertical development of clouds and precipitation
Li, Z., F. Niu, J. Fan, Y. Liu, D. Rosenfeld, Y. Ding
Nature Geoscience, doi:10.1038/ngeo1313 (2011)
We examined the long-term impact of aerosols on the vertical development of clouds and rainfall frequencies using a 10-year dataset of aerosol, cloud and meteorological variables collected in the Southern Great Plains in the United States. Cloud-top height and thickness increased with aerosol concentration measured near the ground in mixed-phase clouds—which contain both liquid water and ice—that have a warm, low base. We attributed the effect, which is most significant in summer, to an aerosol-induced invigoration of upward winds. In contrast, we found no change in cloud-top height and precipitation with aerosol concentration in clouds with no ice or cool bases. Furthermore, rain increased with aerosol concentration in deep clouds that had a high liquid-water content, but declined in clouds with a low liquid-water content. Simulations using a cloud-resolving model confirmed our observations that provide unprecedented insights of the long-term net impacts of aerosols on clouds and precipitation.

Project leader: Dennis Baldocchi
Recent advances in upscaling and data integration across multiple data streams have enabled scientists to produce gridded datasets of regionally and globally explicit flux products.  The sites that comprise Fluxnet and Specnet have become an important source for “bottom-up” inputs to models that upscale flux quantities from canopies to landscapes and from landscapes to the globe.  Data from tower measurements also serve as a validation tool for top-down modeling based on satellite and aircraft optical measurements.  These capabilities have brought climate and ecosystem scientists within reach of quantifying carbon, water and energy fluxes ‘Everywhere, and All of the Time’.  They have also enabled insights into climate-ecosystem interactions and trends over a range of spatial and temporal scales; and particularly at the largest scales.

iLEAPS/GEIA: 1D canopy-atmosphere model evaluation
Leaders: Laurens Ganzeveld (Netherlands) and Alex Guenther (USA)
Project description from iLEAPS Annual Report 2011
This activity is focused on identifying and evaluating 1D canopy models that can be used for investigating canopy scale biogenic emissions, atmospheric deposition and land-surface interactions. The goal is to develop community tools that can be used to design field studies and interpret observations. The first objective was to identify "state-of-the-art" canopy-atmosphere models that have been developed by the scientific community and include canopy emissions, uptake, chemistry and dynamics. All identified groups were invited to participate in the evaluation and a list of 10 models was compiled. A decision was made to initially focus on two biomes: tropical forest and boreal forest. The best available observational databases for these two biomes were identified and an effort was made to obtain these data for the model evaluation activity. These initial efforts have led to the conclusion that existing field observations are lacking for testing these models and additional measurements, including long-term observations, are needed.

iLEAPS/GEIA: Global terrestrial isoprene emission models: sensitivity to variability in climate and vegetation
Arneth, A., Schurgers, G., Lathiere, et al. 2011 
Atmospheric Chemistry and Physics 11, 8037-8052, doi:10.5194/acp-11-8037-2011.
This iLEAPS/GEIA activity was initiated to intercompare global isoprene models that differ in their representation of the vegetation and isoprene emission algorithm. While these models have been evaluated and analyzed individually to ascertain their performance and sensitivity, there had been no systematic analysis of between-model differences and the underlying contributing factors has been made. The chief objectives of this activity were thus to (i) highlight large sources of uncertainties in simulations of global isoprene emissions and to determine the degree of between- vs. within model variation that is introduced by varying some of the models' main features, and to (ii) determine which spatial and/or temporal features were robust between models and different experimental set-ups. When applied in their standard setup, the global isoprene emission models agree on important features regarding global emission totals, spatial distribution, seasonality and interannual variability (see Figure 1). However, the models react sensitively to changes in one or more of the main model components, which was tested with respect to underlying vegetation fields and climate input. The adjustment of individual model features can introduce large variation in annual total emissions. Moreover, "swapping" of standard inputs introduced large changes in simulated seasonality of emission patterns, which could be either a strong dampening or strong acceleration of the observed seasonal cycles, especially in the tropics. From the limited observations available that cover seasonal emissions in tropical regions, neither the absence of seasonally varying emissions nor a hugely pronounced amplitude seems realistic. The increasing number of flux observations, as well as top-down modeling based on satellite derived formaldehyde columns can serve as constraints to test isoprene emission models at least in some regions and some spatial scales and should be the focus of a follow-up iLEAPS/GEIA activity.

iLEAPS/LUCID (Land-Use and Climate: IDentification of robust impacts)
Project leaders: Nathalie de Noblet-Ducoudré and Andy Pitman
Project description from iLEAPS Annual Report 2011
The objectives of LUCID were to identify and quantify the impacts of land-used induced land-cover changes on the evolution of climate between the pre-industrial epoch and present-day. To achieve this, LUCID used a) multi-model and b) ensemble simulations to assess the significance and robustness of the identified changes. To date, we have shown that land-use –induced land-cover change (LULCC) matters at the regional scale and therefore Detection / Attribution studies need to include LULCC. Differences in land surface parameterizations explain ~1/2 to 2/3 of the inter-model dispersion amongst the LUCID results. An implication of this is that we do not fully understand how our land models work, but that we need leadership regarding better ways to evaluate our land surface models. Despite agreement of the before and after maps of land cover, how land cover change was implemented differed strongly. Specifically, the amounts of forests removed explain ~1/3 of the inter-model dispersion. Imagine a region 30% covered with grass and 70% covered by trees pre-human interference. Now, impost 20% crop cover. One can remove grass and replace by crops, one can remove trees and replace by crops or one can spread the crops across these two natural land cover types. Approximately 30% of the differences in the LUCID results stem from how these decisions are taken. The implication is that we need to provide guidance on how LULCC should be actually implemented.

iLEAPS/WATCH: WATCH has highlighted the critical importance of evaporation within the water cycle. In response, it has produced a new global data set of evaporation from land for the period 1984 – 2007 that provides a unique breakdown of the components of evaporation. This breakthrough is due to the availability of high-quality satellite data, coupled with novel and innovative approaches taken by WATCH researchers.  Early analysis of the data appears to support the suggestion that total global land evaporation has reduced over the last ten years. This is contrary to the belief that increasing temperatures due to climate change should cause an increase in global evaporation. The data will allow future studies of global trends, of changes in regional evaporation, and across biomes. WATCH has modelled changes in climate due to changing land use to understand the overall climate-impact of the wide-scale deforestation that has been a feature of the last century. Models agreed that in the key regions, changes to climate could be identified. WATCH has also shown that some changes in land use can reduce evaporation and increase river flows, but that one type of land use – irrigation – has the opposite effect. Overall, the models confirm the need for land-use change to be considered alongside climate change, and any predictions of future climate ought to include the impact of land-use and land-cover change.

iLEAPS/Welgegund observation platform: Record-high new particle formation in semi-clean South African savannah
V. Vakkari, H. Laakso, M. Kulmala, A. Laaksonen, D. Mabaso, M. Molefe, N. Kgabi, and L. Laakso
Atmos. Chem. Phys., 11, 3333–3346, 2011 doi:10.5194/acp-11-3333-2011
We carried out 18 months of continuous measurements of aerosol particle size distributions, air ion size distributions, trace gas concentrations and basic meteorology in a semi-clean savannah environment in Botsalano, Republic of South Africa, as part of the Welgegund observation platform background measurements. New particle formation and growth was observed on 69% of the days and bursts of non-growing ions/sub-10 nm particles on additional 14% of the days. This new particle formation frequency is the highest reported from boundary layer so far. Also the new particle formation and growth rates were among the highest reported in the literature for continental boundary layer locations. The growth rates had a clear seasonal dependency with minimum during winter and maxima in spring and late summer. The relative contribution of estimated sulphuric acid to the growth rate was decreasing with increasing particle size and could explain more than 20% of the observed growth rate only for the 1.5–3 nm size range. Also the air mass history analysis indicated the highest formation and growth rates to be associated with the area of highest VOC (Volatile Organic Compounds) emissions following from biological activity rather than the highest estimated sulphuric acid concentrations. The frequency of new particle formation, however, increased nearly monotonously with the estimated sulphuric acid reaching 100% at H2SO4 concentration of 6·107 cm−3, which suggests the formation and growth to be independent of each other.

Methane emissions from soils: synthesis and analysis of a large UK data set
Peter E. Levy, Annette Burden, Mark D. A. Cooper, et al.
Global Change Biology (accepted article, Dec 2011)
The analysis included nearly 5000 chamber measurements of CH4 flux from 21 sites across the UK, covering a range of soil and vegetation types. Less than half of the observed variability in instantaneous fluxes could be explained by independent variables measured. One important reason was the poor correspondence between the independent variables measured and the actual variables influencing the processes underlying methane production, transport and oxidation. Soil carbon, peat depth, soil moisture and pH together provided the best sub-set of explanatory variables. However, where plant species composition data were available, this provided the highest explanatory power.

Ozone effects in a drier climate: Implications for stomatal fluxes of reduced stomatal sensitivity to soil drying in a typical grassland species
Felicity Hayes, Serena Wagg, Gina Mills, Sally Wilkinson and William Davies
Global Change Biology (accepted article, Dec 2011)
The widely distributed temperate grassland species Dactylis glomerata was grown at two different watering regimes and exposed for 20 weeks to eight ozone treatments representing pre-industrial to predicted post-2100 ozone climates. For the first time, the standard flux model was modified to account for the reduced stomatal sensitivity to soil drying that has been observed to occur with increasing ozone. The standard flux model was found potentially to lead to underestimation of ozone effects in areas where high ozone concentrations and reduced soil moisture coincide. As a consequence, under predicted future climate change and ozone scenarios, ozone effects on vegetation may be even greater than previously predicted in the drier areas of the world.

Uncertainties in climate responses to past land cover change: First results from the LUCID intercomparison study
Pitman AJ, de Noblet-Ducoudré N, Cruz FT, Davin EL, Bonan GB, Brovkin V, Claussen M, Delire C, Ganzeveld L, Gayler V, van den Hurk BJJM, Lawrence PJ, van der Molen MK, Müller C, Reick CH, Seneviratne SI, Strengers BJ, Voldoire A
Geophys. Res. Lett., 36, L14814, doi:10.1029/2009GL039076 (2009)
We used seven climate models to explore the  biogeophysical impacts of human-induced land cover change (LCC) at regional and global scales. The imposed LCC led to  statistically significant decreases in the northern hemisphere summer latent heat flux in three models, and to increases in three models. Five models simulated statistically significant cooling in summer in near-surface temperature over regions of LCC and one simulated warming. There were few significant changes in precipitation. Our results show no common remote impacts of LCC. The lack of consistency among the seven models was due to: 1)  the implementation of LCC despite agreed maps of agricultural land, 2) the representation of crop phenology, 3) the parameterisation of albedo, and 4) the representation of  evapotranspiration for different land cover types. This study highlights a dilemma: LCC is regionally significant, but it is not feasible to impose a common LCC across multiple models for the next IPCC assessment.