This collection gathers papers that present the descriptions, analyses, and evaluations of chemistry–climate model simulations as part of the Chemistry–Climate Model Initiative (CCMI). CCMI is a forum for coordinated inter-model comparisons with and analyses of observations.

Atmospheric chemistry is an integral component of the Earth’s system, playing a role in a wide range of important processes that affect many aspects of the Earth’s environment, including the stratospheric ozone layer, air pollution, and lifetime and fate of a variety of gases and aerosols that affect the Earth’s radiative balance. CCMI works to assess the representation of atmospheric chemistry in global models, including climate and Earth system models, providing projections of how the chemical state of the atmosphere may change in the future and improving our understanding of the interactions between chemistry and climate. To make progress on these goals, CCMI regularly brings together researchers to propose a set of well-defined model experiments to be performed by participating modelling groups, with an accompanying set of diagnostic model output fields. Model data are made available for analysis in a publicly available archive. This collection brings together articles describing the analyses and evaluations of chemistry–climate model data from these sets of CCMI multi-model experiments. CCMI is jointly supported by the Atmospheric Processes and their Role in Climate (APARC) and International Global Atmospheric Chemistry (IGAC) projects.

The FRIDA model is a new integrated assessment model (IAM) for climate, using the tools of system dynamics to integrate the two-way coupling between the human and climate side of the system. Both sides are given equal importance, and we focus as much on the feedbacks and relationships within the system as on the mechanisms within each component (module) of the model. In FRIDA, climate impacts are introduced through a number of process-based impact channels, including impacts on agriculture, energy production, the finance sector, and people's perception of climate risk, all of which are novel aspects of our IAM FRIDA.

FRIDA is developed by a new European team of experts, funded originally through the European Horizon programme. The model is modular - the climate module is developed by climate scientists, the economy module by economists, and so forth.

The model is developed for clarity and intuition building, and it comes with transparent tools for using the model.

This collection gathers papers that describe and/or apply the global water resources and use model WaterGAP.

WaterGAP is a global freshwater model that calculates human water use as well as water flows and storage on all continents (except Antarctica), taking into account the human influence on the natural freshwater system such as climate change, water abstractions, and dams. As one of the pioneers in the field of global hydrological modelling, it supports our understanding of the global freshwater system since 1996 for historical periods and the future. The model is continuously being improved to answer scientific questions driven by societal demands. WaterGAP is applied to assess water scarcity, droughts, and floods and to quantify the human impact on, for example, groundwater, wetlands, streamflow, and sea-level rise.