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Current emissions scenarios include pathways that overshoot the temperature goals set out in the Paris Agreement and rely on future net negative emissions. Limiting overshoot would require near-term investment but would result in longer-term economic benefit. Global emissions scenarios play a critical role in the assessment of strategies to mitigate climate change. The current scenarios, however, are criticized because they feature strategies with pronounced overshoot of the global temperature goal, requiring a long-term repair phase to draw temperatures down again through net-negative emissions. Some impacts might not be reversible. Hence, we explore a new set of net-zero CO2 emissions scenarios with limited overshoot. We show that upfront investments are needed in the near term for limiting temperature overshoot but that these would bring long-term economic gains. Our study further identifies alternative configurations of net-zero CO2 emissions systems and the roles of different sectors and regions for balancing sources and sinks. Even without net-negative emissions, CO2 removal is important for accelerating near-term reductions and for providing an anthropogenic sink that can offset the residual emissions in sectors that are hard to abate.

The urgency with which the world economy needs to be decarbonized could lead to the emergence of regions with the capacity to produce renewable feedstock such as biomass. The competitiveness of these regions could result from their ability to produce high value-added chemicals at the lowest cost. The biomass embodied in a chemical product could reduce carbon emissions, leading to net CO2 removal. The aim of this study was to test the hypothesis that bio-ethylene could make the Brazilian chemical industry more competitive. This would be achieved by applying the revenues from carbon credits associated with using ethanol and sugarcane bagasse as feedstocks for bio-ethylene production. Three production routes were compared according to their estimated cost of production in Brazil under a simplified life-cycle analysis: sugar-cane-derived ethanol to ethylene (with and without CO2 capture and storage – BECCS); bio-methanol to olefin; and conventional steam cracking of naphtha. When associated with the production of long-lasting materials, the ethanol-to-ethylene with BECCS route achieved the lower CO2 break-even price (US$75/t CO2), followed by ethanol to ethylene without BECCS (US$82/t CO2) and bio-methanol to ethylene (US$106/t CO2). Our findings highlight the advantage for the Brazilian chemical industry of implementing a national or, even better, a global carbon-pricing instrument.

Mitigation pathways allowing for temperature overshoot often ignore the related climate and macroeconomic impacts. Net-zero pathways with limited overshoot could reduce low-probability high-consequence risks and economic loss. Mitigation pathways exploring end-of-century temperature targets often entail temperature overshoot. Little is known about the additional climate risks generated by overshooting temperature. Here we assessed the benefits of limiting overshoot. We computed the probabilistic impacts for different warming targets and overshoot levels on the basis of an ensemble of integrated assessment models. We explored both physical and macroeconomic impacts, including persistent and non-persistent climate impacts. We found that temperature overshooting affects the likelihood of many critical physical impacts, such as those associated with heat extremes. Limiting overshoot reduces risk in the right tail of the distribution, in particular for low-temperature targets where larger overshoots arise as a way to lower short-term mitigation costs. We also showed how, after mid-century, overshoot leads to both higher mitigation costs and economic losses from the additional impacts. The study highlights the need to include climate risk analysis in low-carbon pathways.