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).

2016, Rao, Shilpa, Klimont, Zbigniew, Smith, Steven J., Van Dingenen, Rita, Dentener, Frank, Bouwman, Lex, Riahi, Keywan, Amann, Markus, Bodirsky, Benjamin Leon, van Vuuren, Detlef P., Aleluia Reis, Lara, Calvin, Katherine, Drouet, Laurent, Fricko, Oliver, Fujimori, Shinichiro, Gernaat, David, Havlik, Petr, Harmsen, Mathijs, Hasegawa, Tomoko, Heyes, Chris, Hilaire, Jérôme, Luderer, Gunnar, Masui, Toshihiko, Stehfest, Elke, Strefler, Jessica, van der Sluis, Sietske, Tavoni, Massimo

Emissions of air pollutants such as sulfur and nitrogen oxides and particulates have significant health impacts as well as effects on natural and anthropogenic ecosystems. These same emissions also can change atmospheric chemistry and the planetary energy balance, thereby impacting global and regional climate. Long-term scenarios for air pollutant emissions are needed as inputs to global climate and chemistry models, and for analysis linking air pollutant impacts across sectors. In this paper we present methodology and results for air pollutant emissions in Shared Socioeconomic Pathways (SSP) scenarios. We first present a set of three air pollution narratives that describe high, central, and low pollution control ambitions over the 21st century. These narratives are then translated into quantitative guidance for use in integrated assessment models. The resulting pollutant emission trajectories under the SSP scenarios cover a wider range than the scenarios used in previous international climate model comparisons. In the SSP3 and SSP4 scenarios, where economic, institutional and technological limitations slow air quality improvements, global pollutant emissions over the 21st century can be comparable to current levels. Pollutant emissions in the SSP1 scenarios fall to low levels due to the assumption of technological advances and successful global action to control emissions.