The Scenario Model Intercomparison Project for CMIP7 (ScenarioMIP-CMIP7)

Abstract. Scenarios serve as a critical tool in climate change analysis, enabling the exploration of future evolution of the climate system, climate impacts, and the human system (including mitigation and adaptation actions). This paper describes the scenario framework for ScenarioMIP as part of CMIP7. The design process has involved various rounds of interaction with the research community and user groups at large. The proposal covers a set of scenarios exploring high levels of climate change (to explore high-end climate risks), medium levels of climate change (anchored to current policy), and low levels of climate change (aligned with current international agreements). These scenarios follow very different trajectories in terms of emissions, with some likely to experience peaks and subsequent declines in greenhouse gas concentrations in this century. An important innovation is that most scenarios are intended to be run, if possible, in emission-driven mode, providing a better representation of the Earth system uncertainty space. The proposal also includes plans for long-term extensions (up to 2500 AD) to study long-term impacts, climate change-related processes on long timescales, and (ir)reversibility. This proposal forms the basis for further implementation of the framework in terms of the derivation of emissions and land use pathways for use by Earth system models and additional variants for adaptation and mitigation studies.

The Scenario Model Intercomparison Project for CMIP7 (ScenarioMIP-CMIP7)

Abstract. Scenarios serve as a critical tool in climate change analysis, enabling the exploration of future evolution of the climate system, climate impacts, and the human system (including mitigation and adaptation actions). This paper describes the scenario framework for ScenarioMIP as part of CMIP7. The design process has involved various rounds of interaction with the research community and user groups at large. The proposal covers a set of scenarios exploring high levels of climate change (to explore high-end climate risks), medium levels of climate change (anchored to current policy), and low levels of climate change (aligned with current international agreements). These scenarios follow very different trajectories in terms of emissions, with some likely to experience peaks and subsequent declines in greenhouse gas concentrations in this century. An important innovation is that most scenarios are intended to be run, if possible, in emission-driven mode, providing a better representation of the Earth system uncertainty space. The proposal also includes plans for long-term extensions (up to 2500 AD) to study long-term impacts, climate change-related processes on long timescales, and (ir)reversibility. This proposal forms the basis for further implementation of the framework in terms of the derivation of emissions and land use pathways for use by Earth system models and additional variants for adaptation and mitigation studies.

In years to come, the Arctic Ocean will absorb less CO2 than expected

What happens after a snowball Earth melts?

When a snowball Earth deglaciates, the planet transitions rapidly into a hot "supergreenhouse" climate that persists for a hundred thousand years or more - according to the classic snowball Earth theory. In a new publication, MPI-M scientists Lennart Ramme, Tatiana Ilyina and Jochem Marotzke show that this concept is too simplified, as the ocean transformations after a snowball Earth drive strong carbon cycle dynamics, which alter the evolution of atmospheric CO2. In fact, scenarios ranging from a rapid decline to a further intensification of the supergreenhouse climate are possible, depending on the chemical conditions at the start of the snowball Earth deglaciation.