The Paris Agreement-which is aimed at holding global warming well below 2 °C while pursuing efforts to limit it below 1.5 °C-has initiated a bottom-up process of iteratively updating nationally determined contributions to reach these longterm goals. Achieving these goals implies a tight limit on cumulative net CO 2 emissions, of which residual CO 2 emissions from fossil fuels are the greatest impediment. Here, using an ensemble of seven integrated assessment models (IAMs), we explore the determinants of these residual emissions, focusing on sector-level contributions. Even when strengthened pre-2030 mitigation action is combined with very stringent long-term policies, cumulative residual CO 2 emissions from fossil fuels remain at 850-1,150 GtCO 2 during 2016-2100, despite carbon prices of US$130-420 per tCO 2 by 2030. Thus, 640-950 GtCO 2 removal is required for a likely chance of limiting end-of-century warming to 1.5 °C. In the absence of strengthened pre-2030 pledges, long-term CO 2 commitments are increased by 160-330 GtCO 2 , further jeopardizing achievement of the 1.5 °C goal and increasing dependence on CO 2 removal.
Abstract. This paper describes GCAM v5.1, an open source model that
represents the linkages between energy, water, land, climate, and economic
systems. GCAM is a market equilibrium model, is global in scope, and operates
from 1990 to 2100 in 5-year time steps. It can be used to examine, for
example, how changes in population, income, or technology cost might alter
crop production, energy demand, or water withdrawals, or how changes in one
region's demand for energy affect energy, water, and land in other regions.
This paper describes the model, including its assumptions, inputs, and
outputs. We then use 11 scenarios, varying the socioeconomic and climate
policy assumptions, to illustrate the results from the model. The resulting
scenarios demonstrate a wide range of potential future energy, water, and
land uses. We compare the results from GCAM v5.1 to historical data and to
future scenario simulations from earlier versions of GCAM and from other
models. Finally, we provide information on how to obtain the model.
Given the increasing interest in keeping global warming below 1.5°C, a key question is what this would mean for China’s emission pathway, energy restructuring, and decarbonization. By conducting a multimodel study, we find that the 1.5°C-consistent goal would require China to reduce its carbon emissions and energy consumption by more than 90 and 39%, respectively, compared with the “no policy” case. Negative emission technologies play an important role in achieving near-zero emissions, with captured carbon accounting on average for 20% of the total reductions in 2050. Our multimodel comparisons reveal large differences in necessary emission reductions across sectors, whereas what is consistent is that the power sector is required to achieve full decarbonization by 2050. The cross-model averages indicate that China’s accumulated policy costs may amount to 2.8 to 5.7% of its gross domestic product by 2050, given the 1.5°C warming limit.
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