Existing national mitigation pledges and commitments place the world on a path well above the climate goal of the landmark Paris Agreement.  Should the world exceed this limit, it is possible to draw down temperature through sustained use of so-called net-negative emissions (i.e., emitting less CO2 than is taken up by technical and natural processes). RESCUE will expand our current knowledge by exploring the sensitivity of the Earth system to deep mitigation futures which achieve the Paris Agreement goal under different regimes of dependence on net-negative emissions and carbon-dioxide removal.

Meeting the climate ambition laid out on the 2015 Paris Agreement requires significant energy system transformation in conjunction with substantial amounts of Carbon Dioxide Removal (CDR) to achieve a net balance of sources and sinks of Greenhouse Gases (GHGs) in the atmosphere – in other words, net-zero emissions. Scenarios which reach net-zero depend in different degrees on natural and technical CDR, and how the Earth System will respond to such different systems configurations is not well understood. For example, if a temperature target is exceeded before drawing down temperatures with net-negative emissions, it is unclear which fundamental geophysical processes are reversible and which are not. Additionally, dependence on large-scale technical CDR may pose societal risks through increased competition for resources including land and water.

IIASA scientists will contribute to this effort by co-developing the deep mitigation scenarios studied in RESCUE and broadening our understanding of the regional differences across multiple dimensions including CDR deployment, carbon storage, geophysical feedbacks, and localization of climate impacts. These new scenarios will explicitly consider future patterns of land use, including agricultural productivity, in the context of sustainably achieving the global climate goal in order to provide harmonized and consistent data to medium and large-scale Earth system models.

Additionally, IIASA coordinates WP2 with colleagues of the Institut Pierre Simon Laplace -- a work package dedicated to leveraging the flexibility and low computational costs of intermediate and reduced complexity Earth system and integrated assessment models, to run probabilistic and exploratory simulations. These simulations will produce complementary data required by large-scale Earth system models, perform a systematic exploration of physical uncertainty over multi-centennial timescales, explore scenarios with alternative CDR technologies, and assess the risk that land-based CDR technologies cannot meet their assumed potential because of biogeochemical and climate feedbacks.

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