2020, Allen, Robert J., Turnock, Steven, Nabat, Pierre, Neubauer, David, Lohmann, Ulrike, Olivié, Dirk, Oshima, Naga, Michou, Martine, Wu, Tongwen, Zhang, Jie, Takemura, Toshihiko, Schulz, Michael, Tsigaridis, Kostas, Bauer, Susanne E., Emmons, Louisa, Horowitz, Larry, Naik, Vaishali, van Noije, Twan, Bergman, Tommi, Lamarque, Jean-Francois, Zanis, Prodromos, Tegen, Ina, Westervelt, Daniel M., Le Sager, Philippe, Good, Peter, Shim, Sungbo, O’Connor, Fiona, Akritidis, Dimitris, Georgoulias, Aristeidis K., Deushi, Makoto, Sentman, Lori T., John, Jasmin G., Fujimori, Shinichiro, Collins, William J.

It is important to understand how future environmental policies will impact both climate change and air pollution. Although targeting near-term climate forcers (NTCFs), defined here as aerosols, tropospheric ozone, and precursor gases, should improve air quality, NTCF reductions will also impact climate. Prior assessments of the impact of NTCF mitigation on air quality and climate have been limited. This is related to the idealized nature of some prior studies, simplified treatment of aerosols and chemically reactive gases, as well as a lack of a sufficiently large number of models to quantify model diversity and robust responses. Here, we quantify the 2015-2055 climate and air quality effects of non-methane NTCFs using nine state-of-the-art chemistry-climate model simulations conducted for the Aerosol and Chemistry Model Intercomparison Project (AerChemMIP). Simulations are driven by two future scenarios featuring similar increases in greenhouse gases (GHGs) but with weak (SSP3-7.0) versus strong (SSP3-7.0-lowNTCF) levels of air quality control measures. As SSP3-7.0 lacks climate policy and has the highest levels of NTCFs, our results (e.g., surface warming) represent an upper bound. Unsurprisingly, we find significant improvements in air quality under NTCF mitigation (strong versus weak air quality controls). Surface fine particulate matter (PM2:5) and ozone (O3) decrease by 2:20:32 ugm3 and 4:60:88 ppb, respectively (changes quoted here are for the entire 2015-2055 time period; uncertainty represents the 95% confidence interval), over global land surfaces, with larger reductions in some regions including south and southeast Asia. Non-methane NTCF mitigation, however, leads to additional climate change due to the removal of aerosol which causes a net warming effect, including global mean surface temperature and precipitation increases of 0:250:12K and 0:030:012mmd1, respectively. Similarly, increases in extreme weather indices, including the hottest and wettest days, also occur. Regionally, the largest warming and wetting occurs over Asia, including central and north Asia (0:660:20K and 0:030:02mmd1), south Asia (0:470:16K and 0:170:09mmd1), and east Asia (0:460:20K and 0:150:06mmd1). Relatively large warming and wetting of the Arctic also occur at 0:590:36K and 0:040:02mmd1, respectively. Similar surface warming occurs in model simulations with aerosol-only mitigation, implying weak cooling due to ozone reductions. Our findings suggest that future policies that aggressively target non-methane NTCF reductions will improve air quality but will lead to additional surface warming, particularly in Asia and the Arctic. Policies that address other NTCFs including methane, as well as carbon dioxide emissions, must also be adopted to meet climate mitigation goals. © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License.

2020, Hasegawa, Tomoko, Sands, Ronald D., Brunelle, Thierry, Cui, Yiyun, Frank, Stefan, Fujimori, Shinichiro, Popp, Alexander

Bioenergy is expected to play an important role in the achievement of stringent climate-change mitigation targets requiring the application of negative emissions technology. Using a multi-model framework, we assess the effects of high bioenergy demand on global food production, food security, and competition for agricultural land. Various scenarios simulate global bioenergy demands of 100, 200, 300, and 400 exajoules (EJ) by 2100, with and without a carbon price. Six global energy-economy-agriculture models contribute to this study, with different methodologies and technologies used for bioenergy supply and greenhouse-gas mitigation options for agriculture. We find that the large-scale use of bioenergy, if not implemented properly, would raise food prices and increase the number of people at risk of hunger in many areas of the world. For example, an increase in global bioenergy demand from 200 to 300 EJ causes a − 11% to + 40% change in food crop prices and decreases food consumption from − 45 to − 2 kcal person−1 day−1, leading to an additional 0 to 25 million people at risk of hunger compared with the case of no bioenergy demand (90th percentile range across models). This risk does not rule out the intensive use of bioenergy but shows the importance of its careful implementation, potentially including regulations that protect cropland for food production or for the use of bioenergy feedstock on land that is not competitive with food production. © 2020, The Author(s).

2020, Hurtt, George C., Chini, Louise, Sahajpal, Ritvik, Frolking, Steve, Bodirsky, Benjamin L., Calvin, Katherine, Doelman, Jonathan C., Fisk, Justin, Fujimori, Shinichiro, Klein Goldewijk, Kees, Hasegawa, Tomoko, Havlik, Peter, Heinimann, Andreas, Humpenöder, Florian, Jungclaus, Johan, Kaplan, Jed O., Kennedy, Jennifer, Krisztin, Tamás, Lawrence, David, Lawrence, Peter, Ma, Lei, Mertz, Ole, Pongratz, Julia, Popp, Alexander, Poulter, Benjamin, Riahi, Keywan, Shevliakova, Elena, Stehfest, Elke, Thornton, Peter, Tubiello, Francesco N., van Vuuren, Detlef P., Zhang, Xin

Human land use activities have resulted in large changes to the biogeochemical and biophysical properties of the Earth's surface, with consequences for climate and other ecosystem services. In the future, land use activities are likely to expand and/or intensify further to meet growing demands for food, fiber, and energy. As part of the World Climate Research Program Coupled Model Intercomparison Project (CMIP6), the international community has developed the next generation of advanced Earth system models (ESMs) to estimate the combined effects of human activities (e.g., land use and fossil fuel emissions) on the carbon–climate system. A new set of historical data based on the History of the Global Environment database (HYDE), and multiple alternative scenarios of the future (2015–2100) from Integrated Assessment Model (IAM) teams, is required as input for these models. With most ESM simulations for CMIP6 now completed, it is important to document the land use patterns used by those simulations. Here we present results from the Land-Use Harmonization 2 (LUH2) project, which smoothly connects updated historical reconstructions of land use with eight new future projections in the format required for ESMs. The harmonization strategy estimates the fractional land use patterns, underlying land use transitions, key agricultural management information, and resulting secondary lands annually, while minimizing the differences between the end of the historical reconstruction and IAM initial conditions and preserving changes depicted by the IAMs in the future. The new approach builds on a similar effort from CMIP5 and is now provided at higher resolution (0.25∘×0.25∘) over a longer time domain (850–2100, with extensions to 2300) with more detail (including multiple crop and pasture types and associated management practices) using more input datasets (including Landsat remote sensing data) and updated algorithms (wood harvest and shifting cultivation); it is assessed via a new diagnostic package. The new LUH2 products contain > 50 times the information content of the datasets used in CMIP5 and are designed to enable new and improved estimates of the combined effects of land use on the global carbon–climate system.

2019, Stehfest, Elke, van Zeist, Willem-Jan, Valin, Hugo, Havlik, Petr, Popp, Alexander, Kyle, Page, Tabeau, Andrzej, Mason-D’Croz, Daniel, Hasegawa, Tomoko, Bodirsky, Benjamin L., Calvin, Katherine, Doelman, Jonathan C., Fujimori, Shinichiro, Humpenöder, Florian, Lotze-Campen, Hermann, van Meijl, Hans, Wiebe, Keith

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.

2020, Smith, Steven J., Chateau, Jean, Dorheim, Kalyn, Drouet, Laurent, Durand-Lasserve, Olivier, Fricko, Oliver, Fujimori, Shinichiro, Hanaoka, Tatsuya, Harmsen, Mathijs, Hilaire, Jérôme, Keramidas, Kimon, Klimont, Zbigniew, Luderer, Gunnar, Moura, Maria Cecilia P., Riahi, Keywan, Rogelj, Joeri, Sano, Fuminori, van Vuuren, Detlef P., Wada, Kenichi

The relatively short atmospheric lifetimes of methane (CH4) and black carbon (BC) have focused attention on the potential for reducing anthropogenic climate change by reducing Short-Lived Climate Forcer (SLCF) emissions. This paper examines radiative forcing and global mean temperature results from the Energy Modeling Forum (EMF)-30 multi-model suite of scenarios addressing CH4 and BC mitigation, the two major short-lived climate forcers. Central estimates of temperature reductions in 2040 from an idealized scenario focused on reductions in methane and black carbon emissions ranged from 0.18–0.26 °C across the nine participating models. Reductions in methane emissions drive 60% or more of these temperature reductions by 2040, although the methane impact also depends on auxiliary reductions that depend on the economic structure of the model. Climate model parameter uncertainty has a large impact on results, with SLCF reductions resulting in as much as 0.3–0.7 °C by 2040. We find that the substantial overlap between a SLCF-focused policy and a stringent and comprehensive climate policy that reduces greenhouse gas emissions means that additional SLCF emission reductions result in, at most, a small additional benefit of ~ 0.1 °C in the 2030–2040 time frame. © 2020, Battelle Memorial Institute.

2020, Daioglou, Vassilis, Muratori, Matteo, Lamers, Patrick, Fujimori, Shinichiro, Kitous, Alban, Köberle, Alexandre C., Bauer, Nico, Junginger, Martin, Kato, Etsushi, Leblanc, Florian, Mima, Silvana, Wise, Marshal, van Vuuren, Detlef P.

Most climate change mitigation scenarios rely on increased use of bioenergy to decarbonize the energy system. Here we use results from the 33rd Energy Modeling Forum study (EMF-33) to investigate projected international bioenergy trade for different integrated assessment models across several climate change mitigation scenarios. Results show that in scenarios with no climate policy, international bioenergy trade is likely to increase over time, and becomes even more important when climate targets are set. More stringent climate targets, however, do not necessarily imply greater bioenergy trade compared to weaker targets, as final energy demand may be reduced. However, the scaling up of bioenergy trade happens sooner and at a faster rate with increasing climate target stringency. Across models, for a scenario likely to achieve a 2 °C target, 10–45 EJ/year out of a total global bioenergy consumption of 72–214 EJ/year are expected to be traded across nine world regions by 2050. While this projection is greater than the present trade volumes of coal or natural gas, it remains below the present trade of crude oil. This growth in bioenergy trade largely replaces the trade in fossil fuels (especially oil) which is projected to decrease significantly over the twenty-first century. As climate change mitigation scenarios often show diversified energy systems, in which numerous world regions can act as bioenergy suppliers, the projections do not necessarily lead to energy security concerns. Nonetheless, rapid growth in the trade of bioenergy is projected in strict climate mitigation scenarios, raising questions about infrastructure, logistics, financing options, and global standards for bioenergy production and trade. © 2020, The Author(s).

2019, Gidden, Matthew J., Riahi, Keywan, Smith, Steven J., Fujimori, Shinichiro, Luderer, Gunnar, Kriegler, Elmar, van Vuuren, Detlef P., van den Berg, Maarten, Feng, Leyang, Klein, David, Calvin, Katherine, Doelman, Jonathan C., Frank, Stefan, Fricko, Oliver, Harmsen, Mathijs, Hasegawa, Tomoko, Havlik, Petr, Hilaire, Jérôme, Hoesly, Rachel, Horing, Jill, Popp, Alexander, Stehfest, Elke, Takahashi, Kiyoshi

We present a suite of nine scenarios of future emissions trajectories of anthropogenic sources, a key deliverable of the ScenarioMIP experiment within CMIP6. Integrated assessment model results for 14 different emissions species and 13 emissions sectors are provided for each scenario with consistent transitions from the historical data used in CMIP6 to future trajectories using automated harmonization before being downscaled to provide higher emissions source spatial detail. We find that the scenarios span a wide range of end-of-century radiative forcing values, thus making this set of scenarios ideal for exploring a variety of warming pathways. The set of scenarios is bounded on the low end by a 1.9 W m−2 scenario, ideal for analyzing a world with end-of-century temperatures well below 2 ∘C, and on the high end by a 8.5 W m−2 scenario, resulting in an increase in warming of nearly 5 ∘C over pre-industrial levels. Between these two extremes, scenarios are provided such that differences between forcing outcomes provide statistically significant regional temperature outcomes to maximize their usefulness for downstream experiments within CMIP6. A wide range of scenario

2019, Harmsen, Mathijs, Fricko, Oliver, Hilaire, Jérôme, van Vuuren, Detlef P., Drouet, Laurent, Durand-Lasserve, Olivier, Fujimori, Shinichiro, Keramidas, Kimon, Klimont, Zbigniew, Luderer, Gunnar, Aleluia Reis, Lara, Riahi, Keywan, Sano, Fuminori, Smith, Steven J.

Several studies have shown that the greenhouse gas reduction resulting from the current nationally determined contributions (NDCs) will not be enough to meet the overall targets of the Paris Climate Agreement. It has been suggested that more ambition mitigations of short-lived climate forcer (SLCF) emissions could potentially be a way to reduce the risk of overshooting the 1.5 or 2 °C target in a cost-effective way. In this study, we employ eight state-of-the-art integrated assessment models (IAMs) to examine the global temperature effects of ambitious reductions of methane, black and organic carbon, and hydrofluorocarbon emissions. The SLCFs measures considered are found to add significantly to the effect of the NDCs on short-term global mean temperature (GMT) (in the year 2040: − 0.03 to − 0.15 °C) and on reducing the short-term rate-of-change (by − 2 to 15%), but only a small effect on reducing the maximum temperature change before 2100. This, because later in the century under assumed ambitious climate policy, SLCF mitigation is maximized, either directly or indirectly due to changes in the energy system. All three SLCF groups can contribute to achieving GMT changes. © 2019, The Author(s).

2019, Harmsen, Mathijs, Mathijs, Detlef P., Bodirsky, Benjamin Leon, Chateau, Jean, Durand-Lasserve, Olivier, Drouet, Laurent, Fricko, Oliver, Fujimori, Shinichiro, Gernaat, David E.H.J., Hanaoka, Tatsuya, Hilaire, Jérôme, Keramidas, Kimon, Luderer, Gunnar, Moura, Maria Cecilia P., Sano, Fuminori, Smith, Steven J., Wada, Kenichi

This study examines model-specific assumptions and projections of methane (CH4) emissions in deep mitigation scenarios generated by integrated assessment models (IAMs). For this, scenarios of nine models are compared in terms of sectoral and regional CH4 emission reduction strategies, as well as resulting climate impacts. The models’ projected reduction potentials are compared to sector and technology-specific reduction potentials found in literature. Significant cost-effective and non-climate policy related reductions are projected in the reference case (10–36% compared to a “frozen emission factor” scenario in 2100). Still, compared to 2010, CH4 emissions are expected to rise steadily by 9–72% (up to 412 to 654 Mt CH4/year). Ambitious CO2 reduction measures could by themselves lead to a reduction of CH4 emissions due to a reduction of fossil fuels (22–48% compared to the reference case in 2100). However, direct CH4 mitigation is crucial and more effective in bringing down CH4 (50–74% compared to the reference case). Given the limited reduction potential, agriculture CH4 emissions are projected to constitute an increasingly larger share of total anthropogenic CH4 emissions in mitigation scenarios. Enteric fermentation in ruminants is in that respect by far the largest mitigation bottleneck later in the century with a projected 40–78% of total remaining CH4 emissions in 2100 in a strong (2 °C) climate policy case. © 2019, The Author(s).

2020, Ai, Zhipin, Hanasaki, Naota, Heck, Vera, Hasegawa, Tomoko, Fujimori, Shinichiro

Large-scale deployment of bioenergy plantations would have adverse effects on water resources. There is an increasing need to ensure the appropriate inclusion of the bioenergy crops in global hydrological models. Here, through parameter calibration and algorithm improvement, we enhanced the global hydrological model H08 to simulate the bioenergy yield from two dedicated herbaceous bioenergy crops: Miscanthus and switchgrass. Site-specific evaluations showed that the enhanced model had the ability to simulate yield for both Miscanthus and switchgrass, with the calibrated yields being well within the ranges of the observed yield. Independent country-specific evaluations further confirmed the performance of the H08 (v.bio1). Using this improved model, we found that unconstrained irrigation more than doubled the yield under rainfed condition, but reduced the water use efficiency (WUE) by 32 % globally. With irrigation, the yield in dry climate zones can exceed the rainfed yields in tropical climate zones. Nevertheless, due to the low water consumption in tropical areas, the highest WUE was found in tropical climate zones, regardless of whether the crop was irrigated. Our enhanced model provides a new tool for the future assessment of bioenergy–water tradeoffs.