The consequences of uncertainties in land use, climate and vegetation responses on the terrestrial carbon

The IPCC SRES narratives were implemented in IMAGE 2.2 to evaluate thefuture condition of the climate system (including the biosphere). A series of scenario experiments was used to assess possible ranges in emissions and concentrations of greenhouse gases, climate change and impacts. These experiments focussed on the role of the terrestrial carbon cycle. The experiments show that the SRES narratives dominate human emissions and not natural processes. In contrary, atmospheric CO2 concentration strongly differs between the experiments. Atmospheric CO2 concentrations range for A1B from 714 to 1009 ppmv CO2 in 2100. The spread of this range is comparable with the full SRES range as implemented in IMAGE 2.2 (515-895 μmol/mol CO2). The most important negative and positive feedback processes in IMAGE 2.2 on the build-up of CO2 concentrations are CO2 fertilisation and soil respiration respectively. Indirect effects of these processes furtherchange land-use patterns, deforestation rates and alter the natural C fluxes. The cumulative effects of these changes have a pronounced influence on the final CO2 concentrations. Our scenario experiments highlight the importance of a proper parameterisation of feedback processes, C-cycle and land use in determining the future states of the climate system.     

The impact of extensive planting of Miscanthus as an energy crop on future CO2 atmospheric concentrations

A process‐based model of the energy crop Miscanthus×giganteus is integrated into the global climate impact model IMOGEN, simulating the potential of large‐scale Miscanthus plantation to offset fossil fuel emissions during the 21st century. This simulation produces spatially explicit, annual projections of Miscanthus yields from the present day to the year 2100 under an SRES A2 anthropogenic emissions scenario and includes the effects of climate change. IMOGEN also simulates natural vegetation and soil carbon storage throughout the 21st century. The benefit of Miscanthus cultivation (avoiding fossil fuel emissions of CO₂) is then compared with the cost of displacing natural vegetation (carbon emissions from vegetation and soil). The time taken for these effects to cancel out, the pay‐back time, is calculated regionally. The effects of large‐scale Miscanthus plantation are then integrated globally to produce an estimate of atmospheric CO₂ concentrations throughout the 21st century. Our best estimate of the pay‐back time for Miscanthus plantation is 30 years. We project a maximum possible reduction in atmospheric CO₂ of 323 ppmv by the end of 21st century, with a reduction of 162 ppmv corresponding to the best estimate scenario.     

Evaluation of the terrestrial carbon cycle, future plant geography and climate-carbon cycle feedbacks using five Dynamic Global Vegetation Models (DGVMs)

This study tests the ability of five Dynamic Global Vegetation Models (DGVMs), forced with observed climatology and atmospheric CO₂, to model the contemporary global carbon cycle. The DGVMs are also coupled to a fast ‘climate analogue model’, based on the Hadley Centre General Circulation Model (GCM), and run into the future for four Special Report Emission Scenarios (SRES): A1FI, A2, B1, B2. Results show that all DGVMs are consistent with the contemporary global land carbon budget. Under the more extreme projections of future environmental change, the responses of the DGVMs diverge markedly. In particular, large uncertainties are associated with the response of tropical vegetation to drought and boreal ecosystems to elevated temperatures and changing soil moisture status. The DGVMs show more divergence in their response to regional changes in climate than to increases in atmospheric CO₂ content. All models simulate a release of land carbon in response to climate, when physiological effects of elevated atmospheric CO₂ on plant production are not considered, implying a positive terrestrial climate‐carbon cycle feedback. All DGVMs simulate a reduction in global net primary production (NPP) and a decrease in soil residence time in the tropics and extra‐tropics in response to future climate. When both counteracting effects of climate and atmospheric CO₂ on ecosystem function are considered, all the DGVMs simulate cumulative net land carbon uptake over the 21st century for the four SRES emission scenarios. However, for the most extreme A1FI emissions scenario, three out of five DGVMs simulate an annual net source of CO₂ from the land to the atmosphere in the final decades of the 21st century. For this scenario, cumulative land uptake differs by 494 Pg C among DGVMs over the 21st century. This uncertainty is equivalent to over 50 years of anthropogenic emissions at current levels.     

Projected Changes in Terrestrial Carbon Storage in Europe under Climate and Land-use Change, 1990–2100

Changes in climate and land use, caused by socio-economic changes, greenhouse gas emissions, agricultural policies and other factors, are known to affect both natural and managed ecosystems, and will likely impact on the European terrestrial carbon balance during the coming decades. This study presents a comprehensive European Union wide (EU15 plus Norway and Switzerland, EU*) assessment of potential future changes in terrestrial carbon storage considering these effects based on four illustrative IPCC-SRES storylines (A1FI, A2, B1, B2). A process-based land vegetation model (LPJ-DGVM), adapted to include a generic representation of managed ecosystems, is forced with changing fields of land-use patterns from 1901 to 2100 to assess the effect of land-use and cover changes on the terrestrial carbon balance of Europe. The uncertainty in the future carbon balance associated with the choice of a climate change scenario is assessed by forcing LPJ-DGVM with output from four different climate models (GCMs: CGCM2, CSIRO2, HadCM3, PCM2) for the same SRES storyline. Decrease in agricultural areas and afforestation leads to simulated carbon sequestration for all land-use change scenarios with an average net uptake of 17–38 Tg C/year between 1990 and 2100, corresponding to 1.9–2.9% of the EU*s CO₂ emissions over the same period. Soil carbon losses resulting from climate warming reduce or even offset carbon sequestration resulting from growth enhancement induced by climate change and increasing atmospheric CO₂ concentrations in the second half of the twenty-first century. Differences in future climate change projections among GCMs are the main cause for uncertainty in the cumulative European terrestrial carbon uptake of 4.4–10.1 Pg C between 1990 and 2100.     

Modelling terrestrial nitrous oxide emissions and implications for climate feedback

Ecosystem nitrous oxide (N(2) O) emissions respond to changes in climate and CO(2) concentration as well as anthropogenic nitrogen (N) enhancements. Here, we aimed to quantify the responses of natural ecosystem N(2) O emissions to multiple environmental drivers using a process-based global vegetation model (DyN-LPJ). We checked that modelled annual N(2) O emissions from nonagricultural ecosystems could reproduce field measurements worldwide, and experimentally observed responses to step changes in environmental factors. We then simulated global N(2) O emissions throughout the 20th century and analysed the effects of environmental changes. The model reproduced well the global pattern of N(2) O emissions and the observed responses of N cycle components to changes in environmental factors. Simulated 20th century global decadal-average soil emissions were c. 8.2-9.5?Tg?N?yr(-1) (or 8.3-10.3?Tg?N?yr(-1) with N deposition). Warming and N deposition contributed 0.85?±?0.41 and 0.80?±?0.14?Tg?N?yr(-1) , respectively, to an overall upward trend. Rising CO(2) also contributed, in part, through a positive interaction with warming. The modelled temperature dependence of N(2) O emission (c. 1?Tg?N?yr(-1) K(-1) ) implies a positive climate feedback which, over the lifetime of N(2) O (114?yr), could become as important as the climate-carbon cycle feedback caused by soil CO(2) release.     

两种温室气体排放方案下我国水稻产量变化模拟

利用最新的温室气体和SO₂排放方案,即政府间气候变化委员会(IPCC)排放情景特别报告(SRES)的A2和B2方案,通过区域气候模式PRECIS和作物模型CERES-Rcie相嵌套,在50 km×50 km网格尺度下,模拟了未来2080年我国水稻产量的变化.结果表明,两种温室气体排放方案下,我国水稻的年平均单产水平各地有增有减,增产地区主要集中在长江及长江流域以南地区,其中四川和湖北交界的山区增产幅度最大,减产地区主要集中在华北平原和东北平原;由于CO₂的肥效作用,A2温室气体排放方案对我国水稻单产的正面影响大于B2方案,A2排放方案下,我国水稻总产呈现一定程度的上升趋势,B2排放方案下,水稻总产表现为少量下降.     

Disentangling effects of uncertainties on population projections: climate change impact on an epixylic bryophyte

Assessment of future ecosystem risks should account for the relevant uncertainty sources. This means accounting for the joint effects of climate variables and using modelling techniques that allow proper treatment of uncertainties. We investigate the influence of three of the IPCC's scenarios of greenhouse gas emissions (special report on emission scenarios (SRES)) on projections of the future abundance of a bryophyte model species. We also compare the relative importance of uncertainty sources on the population projections. The whole chain global climate model (GCM)-regional climate model-population dynamics model is addressed. The uncertainty depends on both natural- and model-related sources, in particular on GCM uncertainty. Ignoring the uncertainties gives an unwarranted impression of confidence in the results. The most likely population development of the bryophyte Buxbaumia viridis towards the end of this century is negative: even with a low-emission scenario, there is more than a 65 per cent risk for the population to be halved. The conclusion of a population decline is valid for all SRES scenarios investigated. Uncertainties are no longer an obstacle, but a mandatory aspect to include in the viability analysis of populations.     

An integrated approach to improving fossil fuel emissions scenarios with urban ecosystem studies

The future trajectory of fossil fuel emissions is one of the largest uncertainties in predicting climate change. While global emissions scenarios are ultimately of interest for climate modeling, many of the factors that influence energy and fuel consumption operate on a local rather than global level. However, there have been relatively few comprehensive studies of the ecological and socioeconomic processes that will determine the future trajectory of net carbon dioxide (CO₂) emissions at local and regional scales. We conducted an interdisciplinary, whole ecosystem study of the role of climate, urban expansion, urban form, transportation, and the urban forest in influencing net CO₂ emissions in the Salt Lake Valley, Utah, a rapidly urbanizing region in the western U.S. Our approach involved a detailed emissions inventory validated with atmospheric measurements, as well as a system dynamics model of future CO₂ emissions developed in collaboration with local stakeholders. The model highlighted the importance of a positive feedback between urban land development and transportation investments that may strongly affect emissions by amplifying declines in developmental densities and increases in vehicular traffic. Simulations suggested that while doubling the density of tree planting would have a negligible effect on total urban CO₂ emissions, land use and transportation policies that dampen the intensity of the urban sprawl feedback could result in a 22% reduction in CO₂ emissions by 2030 relative to a business as usual scenario. We suggest that by advancing our mechanistic understanding of energy and fuel consumption regionally, this urban ecosystem approach has great potential for improving emissions scenario studies if replicated in other cities and urbanizing regions.     

气候变化情景下中国自然植被净初级生产力分布

基于国际上较通用的Lund-Potsdam-Jena(LPJ)模型,根据中国自然环境特点对其运行机制进行调整,并重新进行了参数化,以B2情景气候数据作为主要的输入数据,以1961-1990年为基准时段,模拟了中国1991-2080自然植被净初级生产力(NPP)对气候变化的响应.结果表明:1961-1990年,中国自然植被的NPP总量为3.06 Pg C·a-1;1961-2080年,NPP总量呈波动下降趋势,且下降速度逐渐加快.在降水相对变化不大的条件下,平均温度的增加对我国植被生产力可能会产生一定的负面影响.NPP的空间分布从东南沿海向西北内陆呈逐渐递减趋势,在气候变化过程中,该格局基本没有太大变化.在东部NPP值相对较高地区,NPP值以减少为主,东北地区、华北东部和黄土高原地区的减少趋势尤为明显;在西部NPP值相对较低地区,NPP以增加趋势为主,青藏高原地区和塔里木盆地的表现尤为突出.随着气候变化的深入,东西部地区这种变化趋势的对比将越发明显.     

Energy crops: current status and future prospects

Energy crops currently contribute a relatively small proportion to the total energy produced from biomass each year, but the proportion is set to grow over the next few decades. This paper reviews the current status of energy crops and their conversion technologies, assesses their potential to contribute to global energy demand and climate mitigation over the next few decades, and examines the future prospects. Previous estimates have suggested a technical potential for energy crops of～400 EJ yr^?1 by 2050. In a new analysis based on energy crop areas for each of the IPCC SRES scenarios in 2025 (as projected by the IMAGE 2.2 integrated assessment model), more conservative dry matter and energy yield estimates and an assessment of the impact on non‐CO₂ greenhouse gases were used to estimate the realistically achievable potential for energy crops by 2025 to be between 2 and 22 EJ yr^?1, which will offset～100–2070 Mt CO₂‐eq. yr^?1. These results suggest that additional production of energy crops alone is not sufficient to reduce emissions to meet a 550 μmol mol^?1 atmospheric CO₂ stabilization trajectory, but is sufficient to form an important component in a portfolio of climate mitigation measures, as well as to provide a significant sustainable energy resource to displace fossil fuel resources. Realizing the potential of energy crops will necessitate optimizing the dry matter and energy yield of these crops per area of land through the latest biotechnological routes, with or without the need for genetic modification. In future, the co‐benefits of bioenergy production will need to be optimized and methods will need to be developed to extract and refine high‐value products from the feedstock before it is used for energy production.     

Forecasting the Effects of Land Use Scenarios on Farmland Birds Reveal a Potential Mitigation of Climate Change Impacts

Climate and land use changes are key drivers of current biodiversity trends, but interactions between these drivers are poorly modeled, even though they could amplify or mitigate negative impacts of climate change. Here, we attempt to predict the impacts of different agricultural change scenarios on common breeding birds within farmland included in the potential future climatic suitable areas for these species. We used the Special Report on Emissions Scenarios (SRES) to integrate likely changes in species climatic suitability, based on species distribution models, and changes in area of farmland, based on the IMAGE model, inside future climatic suitable areas. We also developed six farmland cover scenarios, based on expert opinion, which cover a wide spectrum of potential changes in livestock farming and cropping patterns by 2050. We ran generalized linear mixed models to calibrate the effects of farmland cover and climate change on bird specific abundance within 386 small agricultural regions. We used model outputs to predict potential changes in bird populations on the basis of predicted changes in regional farmland cover, in area of farmland and in species climatic suitability. We then examined the species sensitivity according to their habitat requirements. A scenario based on extensification of agricultural systems (i.e., low-intensity agriculture) showed the greatest potential to reduce reverse current declines in breeding birds. To meet ecological requirements of a larger number of species, agricultural policies accounting for regional disparities and landscape structure appear more efficient than global policies uniformly implemented at national scale. Interestingly, we also found evidence that farmland cover changes can mitigate the negative effect of climate change. Here, we confirm that there is a potential for countering negative effects of climate change by adaptive management of landscape. We argue that such studies will help inform sustainable agricultural policies for the future.     

Downy mildew (Plasmopara viticola) epidemics on grapevine under climate change

As climate is a key agro‐ecosystem driving force, climate change could have a severe impact on agriculture. Many assessments have been carried out to date on the possible effects of climate change (temperature, precipitation and carbon dioxide concentration changes) on plant physiology. At present however, likely effects on plant pathogens have not been investigated deeply. The aim of this work was to simulate future scenarios of downy mildew (Plasmopara viticola) epidemics on grape under climate change, by combining a disease model to output from two general circulation models (GCMs). Model runs corresponding to the SRES‐A2 emissions scenario, characterized by high projections of both population and greenhouse gas emissions from present to 2100, were chosen in order to investigate impacts of worst‐case scenarios, among those currently available from IPCC. Three future decades were simulated (2030, 2050, 2080), using as baseline historical series of meteorological data collected from 1955 to 2001 in Acqui Terme, an important grape‐growing area in the north‐west of Italy. Both GCMs predicted increase of temperature and decrease of precipitation in this region. The simulations obtained by combining the disease model to the two GCM outputs predicted an increase of the disease pressure in each decade: more severe epidemics were a direct consequence of more favourable temperature conditions during the months of May and June. These negative effects of increasing temperatures more than counterbalanced the effects of precipitation reductions, which alone would have diminished disease pressure. Results suggested that, as adaptation response to future climate change, more attention would have to be paid in the management of early downy mildew infections; two more fungicide sprays were necessary under the most negative climate scenario, compared with present management regimes. At the same time, increased knowledge on the effects of climate change on host–pathogen interactions will be necessary to improve current predictions.     

全球气候变化下中国亚热带地区柑桔气候适宜性

选取亚热带地区273个气象站1961—2008年逐日气象资料,结合IPCC SRES A2情景下未来亚热带地区温度、降水模拟数据,应用作物气候适宜度模型,对中国亚热带地区柑桔的气候适宜性变化进行了研究。结果表明:柑桔气候适宜度变化受到温度的主导,其空间分布趋势同温度适宜度变化基本一致;未来气候情景下柑桔气候适宜度变化大致呈纬度地带性分布,随着纬度的升高其气候适宜度变化由下降变为上升,可以分为强下降型(Ⅰ)、弱下降型(Ⅱ)、弱上升型(Ⅲ)和强上升型(Ⅳ)4种类型;基本上以温州-金华-浦城-乐平-英山-武汉-石门-吉首-武冈-通道-独山-望谟-广南-屏边-澜沧一线为界,其南气候适宜度有所下降,其北有所上升;亚热带西部柑桔气候适宜度上升较大。     

Assessing the impacts of climate change and land transformation on Banksia in the South West Australian Floristic Region

Aim To determine the potential combined effects of climate change and land transformation on the modelled geographic ranges of Banksia. Location Mediterranean climate South West Australian Floristic Region (SWAFR). Methods We used the species distribution modelling software Maxent to relate current environmental conditions to occurrence data for 18 Banksia species, and subsequently made spatial predictions using two simple dispersal scenarios (zero and universal), for three climate‐severity scenarios at 2070, taking the impacts of land transformation on species’ ranges into account. The species were chosen to reflect the biogeography of Banksia in the SWAFR. Results Climate‐severity scenario, dispersal scenario, biogeographic distribution and land transformation all influenced the direction and magnitude of the modelled range change responses for the 18 species. The predominant response of species to all climate change scenarios was range contraction, with exceptions for some northern and widespread species. Including land transformation in estimates of modelled geographic range size for the three climate‐severity scenarios generally resulted in smaller gains and larger declines in species ranges across both dispersal scenarios. Including land transformation and assuming zero dispersal resulted, as expected, in the greatest declines in projected range size across all species. Increasing climate change severity greatly increased the risk of decline in the 18 Banksia species, indicating the critical role of mitigating future emissions. Main conclusions The combined effects of climate change and land transformation may have significant adverse impacts on endemic Proteaceae in the SWAFR, especially under high emissions scenarios and if, as expected, natural migration is limiting. Although these results need cautious interpretation in light of the many assumptions underlying the techniques used, the impacts identified warrant a clear focus on monitoring across species ranges to detect early signs of change, and experiments that determine physiological thresholds for species in order to validate and refine the models.     

Stage‐dependent physiological responses in a butterfly cause non‐additive effects on phenology

Studies illustrating climate‐induced shifts in phenology typically focus on the timing of a single lifecycle stage. In contrast, species’ responses to climate change are likely to be complex and constrained by interactions and tradeoffs across the lifecycle. We characterized the thermal sensitivity of egg, larval and pupal stages of a native Australian butterfly and then integrated these responses to predict sensitivity of emergence time, survival, and feeding performance on oviposition date and climate. Thermal physiology varied among lifecycle stages and between sexes, with the development rate of eggs, first instar larvae, and pupae being the most sensitive to temperature. As lifecycle stages have different thermal physiologies, the environment experienced by a given stage depends in a complex way on the experience of previous stages. Our simulations indicate that oviposition date strongly influences time spent in each lifecycle‐stage, as well as performance. Under a high emissions climate warming scenario (CSIRO Mk 3.5 climate model, high emissions SRES marker scenario A1F1, and a moderate rate of global warming), we predict development times to decrease by 38 days by 2070. Our analysis illustrates how differences in thermal physiology across the lifecycle may result in non‐additive effects on phenology which, in turn, may constrain species’ responses to global warming. These results highlight the need to view shifts in phenology in the context of an organism's entire lifecycle.     

Influence of dimethyl sulfide on the carbon cycle and biological production

Dimethyl sulfide (DMS) is a significant source of marine sulfate aerosol and plays an important role in modifying cloud properties. Fully coupled climate simulations using dynamic marine ecosystem and DMS calculations are conducted to estimate DMS fluxes under various climate scenarios and to examine the sign and strength of phytoplankton-DMS-climate feedbacks for the first time. Simulation results show small differences in the DMS production and emissions between pre-industrial and present climate scenarios, except for some areas in the Southern Ocean. There are clear changes in surface ocean DMS concentrations moving into the future, and they are attributable to changes in phytoplankton production and competition driven by complex spatially varying mechanisms. Comparisons between parallel simulations with and without DMS fluxes into the atmosphere show significant differences in marine ecosystems and physical fields. Without DMS, the missing subsequent aerosol indirect effects on clouds and radiative forcing lead to fewer clouds, more solar radiation, and a much warmer climate. Phaeocystis, a uniquely efficient organosulfur producer with a growth advantage under cooler climate states, can benefit from producing the compound through cooling effects of DMS in the climate system. Our results show a tight coupling between the sulfur and carbon cycles. The ocean carbon uptake declines without DMS emissions to the atmosphere. The analysis indicates a weak positive phytoplankton-DMS-climate feedback at the global scale, with large spatial variations driven by individual autotrophic functional groups and complex mechanisms. The sign and strength of the feedback vary with climate states and phytoplankton groups. This highlights the importance of a dynamic marine ecosystem module and the sulfur cycle mechanism in climate projections.     

Mechanistic insights into the effects of climate change on larval cod

Understanding the biophysical mechanisms that shape variability in fisheries recruitment is critical for estimating the effects of climate change on fisheries. In this study, we used an Earth System Model (ESM) and a mechanistic individual‐based model (IBM) for larval fish to analyze how climate change may impact the growth and survival of larval cod in the North Atlantic. We focused our analysis on five regions that span the current geographical range of cod and are known to contain important spawning populations. Under the SRES A2 (high emissions) scenario, the ESM‐projected surface ocean temperatures are expected to increase by >1 °C for 3 of the 5 regions, and stratification is expected to increase at all sites between 1950–1999 and 2050–2099. This enhanced stratification is projected to decrease large (>5 μm ESD) phytoplankton productivity and mesozooplankton biomass at all 5 sites. Higher temperatures are projected to increase larval metabolic costs, which combined with decreased food resources will reduce larval weight, increase the probability of larvae dying from starvation and increase larval exposure to visual and invertebrate predators at most sites. If current concentrations of piscivore and invertebrate predators are maintained, larval survival is projected to decrease at all five sites by 2050–2099. In contrast to past observed responses to climate variability in which warm anomalies led to better recruitment in cold‐water stocks, our simulations indicated that reduced prey availability under climate change may cause a reduction in larval survival despite higher temperatures in these regions. In the lower prey environment projected under climate change, higher metabolic costs due to higher temperatures outweigh the advantages of higher growth potential, leading to negative effects on northern cod stocks. Our results provide an important first large‐scale assessment of the impacts of climate change on larval cod in the North Atlantic.     

Water use and yield of bioenergy poplar in future climates: modelling the interactive effects of elevated atmospheric CO2 and climate on productivity and water use

Vegetation exerts large control on global biogeochemical cycles through the processes of photosynthesis and transpiration that exchange CO₂ and water between the land and the atmosphere. Increasing atmospheric CO₂ concentrations exert direct effects on vegetation through enhanced photosynthesis and reduced stomatal conductance, and indirect effects through changes in climatic variables that drive these processes. How these direct and indirect CO₂ impacts interact with each other to affect plant productivity and water use has not been explicitly analysed and remains unclear, yet is important to fully understand the response of the global carbon cycle to future climate change. Here, we use a set of factorial modelling experiments to quantify the direct and indirect impacts of atmospheric CO₂ and their interaction on yield and water use in bioenergy short rotation coppice poplar, in addition to quantifying the impact of other environmental drivers such as soil type. We use the JULES land‐surface model forced with a ten‐member ensemble of projected climate change for 2100 with atmospheric CO₂ concentrations representative of the A1B emissions scenario. We show that the simulated response of plant productivity to future climate change was nonadditive in JULES, however this nonadditivity was not apparent for plant transpiration. The responses of both growth and transpiration under all experimental scenarios were highly variable between sites, highlighting the complexity of interactions between direct physiological CO₂ effects and indirect climate effects. As a result, no general pattern explaining the response of bioenergy poplar water use and yield to future climate change could be discerned across sites. This study suggests attempts to infer future climate change impacts on the land biosphere from studies that force with either the direct or indirect CO₂ effects in isolation from each other may lead to incorrect conclusions in terms of both the direction and magnitude of plant response to future climate change.     

Balance between climate change mitigation benefits and land use impacts of bioenergy: conservation implications for European birds

Both climate change and habitat modification exert serious pressure on biodiversity. Although climate change mitigation has been identified as an important strategy for biodiversity conservation, bioenergy remains a controversial mitigation action due to its potential negative ecological and socio-economic impacts which arise through habitat modification by land use change. While the debate continues, the separate or simultaneous impacts of both climate change and bioenergy on biodiversity have not yet been compared. We assess projected range shifts of 156 European bird species by 2050 under two alternative climate change trajectories: a baseline scenario, where the global mean temperature increases by 4 °C by the end of the century, and a 2 degrees scenario, where global concerted effort limits the temperature increase to below 2 °C. For the latter scenario, we also quantify the pressure exerted by increased cultivation of energy biomass as modelled by IMAGE2.4, an integrated land use model. The global bioenergy use in this scenario is in the lower end of the range of previously estimated sustainable potential. Under the assumptions of these scenarios, we find that the magnitude of range shifts due to climate change is far greater than the impact of land conversion to woody bioenergy plantations within the European Union, and that mitigation of climate change reduces the exposure experienced by species. However, we identified potential for local conservation conflict between priority areas for conservation and bioenergy production. These conflicts must be addressed by strict bioenergy sustainability criteria that acknowledge biodiversity conservation needs beyond existing protected areas and apply also to biomass imported from outside the European Union.     

Large uncertainty in carbon uptake potential of land‐based climate‐change mitigation efforts

Most climate mitigation scenarios involve negative emissions, especially those that aim to limit global temperature increase to 2°C or less. However, the carbon uptake potential in land‐based climate change mitigation efforts is highly uncertain. Here, we address this uncertainty by using two land‐based mitigation scenarios from two land‐use models (IMAGE and MAgPIE) as input to four dynamic global vegetation models (DGVMs; LPJ‐GUESS, ORCHIDEE, JULES, LPJmL). Each of the four combinations of land‐use models and mitigation scenarios aimed for a cumulative carbon uptake of ~130 GtC by the end of the century, achieved either via the cultivation of bioenergy crops combined with carbon capture and storage (BECCS) or avoided deforestation and afforestation (ADAFF). Results suggest large uncertainty in simulated future land demand and carbon uptake rates, depending on the assumptions related to land use and land management in the models. Total cumulative carbon uptake in the DGVMs is highly variable across mitigation scenarios, ranging between 19 and 130 GtC by year 2099. Only one out of the 16 combinations of mitigation scenarios and DGVMs achieves an equivalent or higher carbon uptake than achieved in the land‐use models. The large differences in carbon uptake between the DGVMs and their discrepancy against the carbon uptake in IMAGE and MAgPIE are mainly due to different model assumptions regarding bioenergy crop yields and due to the simulation of soil carbon response to land‐use change. Differences between land‐use models and DGVMs regarding forest biomass and the rate of forest regrowth also have an impact, albeit smaller, on the results. Given the low confidence in simulated carbon uptake for a given land‐based mitigation scenario, and that negative emissions simulated by the DGVMs are typically lower than assumed in scenarios consistent with the 2°C target, relying on negative emissions to mitigate climate change is a highly uncertain strategy.