Afforestation is considered a cost‐effective and readily available climate change mitigation option. In recent studies afforestation is presented as a major solution to limit climate change. However, ...estimates of afforestation potential vary widely. Moreover, the risks in global mitigation policy and the negative trade‐offs with food security are often not considered. Here we present a new approach to assess the economic potential of afforestation with the IMAGE 3.0 integrated assessment model framework. In addition, we discuss the role of afforestation in mitigation pathways and the effects of afforestation on the food system under increasingly ambitious climate targets. We show that afforestation has a mitigation potential of 4.9 GtCO2/year at 200 US$/tCO2 in 2050 leading to large‐scale application in an SSP2 scenario aiming for 2°C (410 GtCO2 cumulative up to 2100). Afforestation reduces the overall costs of mitigation policy. However, it may lead to lower mitigation ambition and lock‐in situations in other sectors. Moreover, it bears risks to implementation and permanence as the negative emissions are increasingly located in regions with high investment risks and weak governance, for example in Sub‐Saharan Africa. Afforestation also requires large amounts of land (up to 1,100 Mha) leading to large reductions in agricultural land. The increased competition for land could lead to higher food prices and an increased population at risk of hunger. Our results confirm that afforestation has substantial potential for mitigation. At the same time, we highlight that major risks and trade‐offs are involved. Pathways aiming to limit climate change to 2°C or even 1.5°C need to minimize these risks and trade‐offs in order to achieve mitigation sustainably.
Afforestation is often presented as a key climate change mitigation option, but potential risks and trade‐offs are generally disregarded. In this study we show afforestation has large potential for mitigation, which could reduce overall costs. However, we also show there could be major risks regarding implementation and permanence as well as large trade‐offs with food security. Pathways aiming to limit climate change to 2°C or even 1.5°C need to minimize these risks and trade‐offs in order to achieve mitigation sustainably.
Land use is at the core of various sustainable development goals. Long-term climate foresight studies have structured their recent analyses around five socio-economic pathways (SSPs), with consistent ...storylines of future macroeconomic and societal developments; however, model quantification of these scenarios shows substantial heterogeneity in land-use projections. Here we build on a recently developed sensitivity approach to identify how future land use depends on six distinct socio-economic drivers (population, wealth, consumption preferences, agricultural productivity, land-use regulation, and trade) and their interactions. Spread across models arises mostly from diverging sensitivities to long-term drivers and from various representations of land-use regulation and trade, calling for reconciliation efforts and more empirical research. Most influential determinants for future cropland and pasture extent are population and agricultural efficiency. Furthermore, land-use regulation and consumption changes can play a key role in reducing both land use and food-security risks, and need to be central elements in sustainable development strategies.
Scenario‐based biodiversity modelling is a powerful approach to evaluate how possible future socio‐economic developments may affect biodiversity. Here, we evaluated the changes in terrestrial ...biodiversity intactness, expressed by the mean species abundance (MSA) metric, resulting from three of the shared socio‐economic pathways (SSPs) combined with different levels of climate change (according to representative concentration pathways RCPs): a future oriented towards sustainability (SSP1xRCP2.6), a future determined by a politically divided world (SSP3xRCP6.0) and a future with continued global dependency on fossil fuels (SSP5xRCP8.5). To this end, we first updated the GLOBIO model, which now runs at a spatial resolution of 10 arc‐seconds (~300 m), contains new modules for downscaling land use and for quantifying impacts of hunting in the tropics, and updated modules to quantify impacts of climate change, land use, habitat fragmentation and nitrogen pollution. We then used the updated model to project terrestrial biodiversity intactness from 2015 to 2050 as a function of land use and climate changes corresponding with the selected scenarios. We estimated a global area‐weighted mean MSA of 0.56 for 2015. Biodiversity intactness declined in all three scenarios, yet the decline was smaller in the sustainability scenario (−0.02) than the regional rivalry and fossil‐fuelled development scenarios (−0.06 and −0.05 respectively). We further found considerable variation in projected biodiversity change among different world regions, with large future losses particularly for sub‐Saharan Africa. In some scenario‐region combinations, we projected future biodiversity recovery due to reduced demands for agricultural land, yet this recovery was counteracted by increased impacts of other pressures (notably climate change and road disturbance). Effective measures to halt or reverse the decline of terrestrial biodiversity should not only reduce land demand (e.g. by increasing agricultural productivity and dietary changes) but also focus on reducing or mitigating the impacts of other pressures.
We project the changes in terrestrial biodiversity intactness from 2015 to 2050 corresponding with three of the shared socio‐economic pathways combined with different levels of climate change, using an updated version of the GLOBIO model. Biodiversity intactness declined in all three scenarios, with large losses particularly for sub‐Saharan Africa. Effective measures to halt or reverse the decline of terrestrial biodiversity should not only reduce land demand but also reduce or mitigate the impacts of other pressures.
A fundamental and ubiquitous phenomenon in chemistry is the contraction of both C−H and C−C bonds as the carbon atoms involved vary, in s–p hybridization, along sp3 to sp2 to sp. Our quantum chemical ...bonding analyses based on Kohn–Sham molecular orbital theory show that the generally accepted rationale behind this trend is incorrect. Inspection of the molecular orbitals and their corresponding orbital overlaps reveals that the above‐mentioned shortening in C−H and C−C bonds is not determined by an increasing amount of s‐character at the carbon atom in these bonds. Instead, we establish that this structural trend is caused by a diminishing steric (Pauli) repulsion between substituents around the pertinent carbon atom, as the coordination number decreases along sp3 to sp2 to sp.
A paradigm shift! Our quantum chemical analyses reveal that, for example, C−H bonds along ethane, ethylene, and acetylene, do not contract due to the changing s–p hybridization of the pertinent carbon atom from sp3 to sp2 to sp but, instead, because the steric congestion around this carbon atom decreases as the coordination number goes from 4 to 3 to 2.
We have quantum chemically investigated how methyl substituents affect the stability of alkyl radicals MemH3−mC⋅ and the corresponding MemH3−mC−X bonds (X = H, CH3, OH; m = 0 – 3) using density ...functional theory at M06‐2X/TZ2P. The state‐of‐the‐art in physical organic chemistry is that alkyl radicals are stabilized upon an increase in their degree of substitution from methyl<primary<secondary<tertiary, and that this is the underlying cause for the decrease in C−H bond strength along this series. Here, we provide evidence that falsifies this model and show that, on the contrary, the MemH3−mC⋅ radical is destabilized with increasing substitution. The reason that the corresponding C−H bond nevertheless becomes weaker is that substitution destabilizes the sterically more congested MemH3−mC−H molecule even more.
Radical stability decreases, and not increases, from methyl to primary to secondary to tertiary. This is not conflicting with the fact that the C−H bond becomes weaker along the corresponding series H3C−H, MeH2C−H, Me2HC−H, and Me3C−H. The resolution to this seeming contradiction is that the parent MemH3−mC−H is destabilized even more upon methyl substitution than the radical MemH3−mC⋅.
The C−X bond activation (X = H, C) of a series of substituted C(n°)−H and C(n°)−C(m°) bonds with C(n°) and C(m°) = H3C− (methyl, 0°), CH3H2C− (primary, 1°), (CH3)2HC− (secondary, 2°), (CH3)3C− ...(tertiary, 3°) by palladium were investigated using relativistic dispersion‐corrected density functional theory at ZORA‐BLYP‐D3(BJ)/TZ2P. The effect of the stepwise introduction of substituents was pinpointed at the C−X bond on the bond activation process. The C(n°)−X bonds become substantially weaker going from C(0°)−X, to C(1°)−X, to C(2°)−X, to C(3°)−X because of the increasing steric repulsion between the C(n°)‐ and X‐group. Interestingly, this often does not lead to a lower barrier for the C(n°)−X bond activation. The C−H activation barrier, for example, decreases from C(0°)−X, to C(1°)−X, to C(2°)−X and then increases again for the very crowded C(3°)−X bond. For the more congested C−C bond, in contrast, the activation barrier always increases as the degree of substitution is increased. Our activation strain and matching energy decomposition analyses reveal that these differences in C−H and C−C bond activation can be traced back to the opposing interplay between steric repulsion across the C−X bond versus that between the catalyst and substrate.
Bulk up! Our computational study shows how increasing steric bulk at the C−X bond systematically decreases the bond strength along the series C(0°)−X to C(1°)−X to C(2°)−X to C(3°)−X. These weaker C−H and C−C bonds are not always more reactive in oxidative addition reactions with palladium catalysts. Instead, we illustrate the interplay between steric repulsion across the C−X bond versus that of the catalyst and substrate.
We have studied the palladium‐mediated activation of C(spn)−X bonds (n = 1–3 and X = H, CH3, Cl) in archetypal model substrates H3C−CH2−X, H2C=CH−X and HC≡C−X by catalysts PdLn with Ln = no ligand, ...Cl−, and (PH3)2, using relativistic density functional theory at ZORA‐BLYP/TZ2P. The oxidative addition barrier decreases along this series, even though the strength of the bonds increases going from C(sp3)−X, to C(sp2)−X, to C(sp)−X. Activation strain and matching energy decomposition analyses reveal that the decreased oxidative addition barrier going from sp3, to sp2, to sp, originates from a reduction in the destabilizing steric (Pauli) repulsion between catalyst and substrate. This is the direct consequence of the decreasing coordination number of the carbon atom in C(spn)−X, which goes from four, to three, to two along this series. The associated net stabilization of the catalyst–substrate interaction dominates the trend in strain energy which indeed becomes more destabilizing along this same series as the bond becomes stronger from C(sp3)−X to C(sp)−X.
Less is more! Our quantum chemical analyses reveal that the activity of palladium catalysts towards C−X bond activation increases along ethane, ethylene, acetylene because the steric repulsion between catalyst and substrate is relieved as the number of substituents around the carbon atom goes down.
The EU's Green Deal sets out a vision for a clean, competitive, climate neutral circular economy. As a part-solution for decarbonising its industrial base and improving its strategic autonomy, the ...role of bio-based substitutes is envisaged. Focusing on EU chemicals, the MAGNET simulation model is employed to quantify the impacts from EU bio-based chemical, pharmaceutical and plastic output increases over a thirty-year time horizon to 2050. To support this transformation, a fiscally-neutral tax funded investment scheme is modelled. Results show EU bioeconomy (rural) employment and growth improvements, although bio-feedstock market tensions impact negatively on EU food security, whilst ‘leakage’ effects cause net global increases in greenhouse gases and land use. Further experiments explore (i) sustainable tax schemes on food-based feedstock to mitigate said tensions and (ii) green-investment driven input-saving productivity gains in EU bio-based chemicals. Employing metrics for the five bioeconomy strategy objectives, the former generates environmental, food and (bio-)energy security improvements, relieves land market tensions, but falls short of a win-win/win-neutral outcome. Similarly, for four EU bioeconomy objectives, the latter produces outcomes that are largely on a par, or even better than the baseline. Finally, a stylised combination of both is found to generate the most optimal outcomes.
Systematic model inter-comparison helps to narrow discrepancies in the analysis of the future impact of climate change on agricultural production. This paper presents a set of alternative scenarios ...by five global climate and agro-economic models. Covering integrated assessment (IMAGE), partial equilibrium (CAPRI, GLOBIOM, MAgPIE) and computable general equilibrium (MAGNET) models ensures a good coverage of biophysical and economic agricultural features. These models are harmonized with respect to basic model drivers, to assess the range of potential impacts of climate change on the agricultural sector by 2050. Moreover, they quantify the economic consequences of stringent global emission mitigation efforts, such as non-CO2 emission taxes and land-based mitigation options, to stabilize global warming at 2 °C by the end of the century under different Shared Socioeconomic Pathways. A key contribution of the paper is a vis-à-vis comparison of climate change impacts relative to the impact of mitigation measures. In addition, our scenario design allows assessing the impact of the residual climate change on the mitigation challenge. From a global perspective, the impact of climate change on agricultural production by mid-century is negative but small. A larger negative effect on agricultural production, most pronounced for ruminant meat production, is observed when emission mitigation measures compliant with a 2 °C target are put in place. Our results indicate that a mitigation strategy that embeds residual climate change effects (RCP2.6) has a negative impact on global agricultural production relative to a no-mitigation strategy with stronger climate impacts (RCP6.0). However, this is partially due to the limited impact of the climate change scenarios by 2050. The magnitude of price changes is different amongst models due to methodological differences. Further research to achieve a better harmonization is needed, especially regarding endogenous food and feed demand, including substitution across individual commodities, and endogenous technological change.
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