The MESSAGE Integrated Assessment Model (IAM) developed by IIASA has been a central tool of energy-environment-economy systems analysis in the global scientific and policy arena. It played a major role in the Assessment Reports of the Intergovernmental Panel on Climate Change (IPCC); it provided marker scenarios of the Representative Concentration Pathways (RCPs) and the Shared SocioEconomic Pathways (SSPs); and it underpinned the analysis of the Global Energy Assessment (GEA). Alas, to provide relevant analysis for current and future challenges, numerical models of human and earth systems need to support higher spatial and temporal resolution, facilitate integration of data sources and methodologies across disciplines, and become open and transparent regarding the underlying data, methods, and the scientific workflow. In this manuscript, we present the building blocks of a new framework for an integrated assessment modeling platform; the "ecosystem" comprises: i) an open-source GAMS implementation of the MESSAGE energy++ system model integrated with the MACRO economic model; ii) a Java/database backend for version-controlled data management, iii) interfaces for the scientific programming languages Python & R for efficient input data and results processing workflows; and iv) a web-browser-based user interface for model/scenario management and intuitive "drag-and-drop" visualization of results. The framework aims to facilitate the highest level of openness for scientific analysis, bridging the need for transparency with efficient data processing and powerful numerical solvers. The platform is geared towards easy integration of data sources and models across disciplines, spatial scales and temporal disaggregation levels. All tools apply best-practice in collaborative software development, and comprehensive documentation of all building blocks and scripts is generated directly from the GAMS equations and the Java/Python/R source code.

To feed a rapidly growing population of 250 million, the Indus river basin in South Asia is one of the most intensively cultivated regions on Earth, highly water stressed and lacking energy security. Yet, most studies advising sustainable development policy have lacked multi-sectoral and cross-country perspectives. Here we show how the Indus countries could lower costs for development and reduce soil pollution and water stress, by cooperating on water resources and electricity and food production. According to this analysis, Indus basin countries need to ramp up investments to 10 billion USD/year to mitigate water scarcity issues and ensure improved access to resources by 2050. These costs could shrink to 2 billion USD/year, with economic gains for all, if countries pursued more collaborative policies. Downstream regions would benefit the most, with reduced food and energy costs and better water access, while upstream regions would benefit from new energy investments. Using integrated water-energy-land analysis, this study quantifies the potential benefits for novel avenues to sustainable development arising from greater international cooperation.

The COVID-19 pandemic caused radical temporary breaks with past energy use trends. How post-pandemic recovery will impact the longer-term energy transition is unclear. Here we present a set of global COVID-19 shock-and-recovery scenarios that systematically explore the effect of demand changes persisting. Our pathways project final energy demand reductions of 1-36 EJ yr −1 by 2025 and cumulative CO 2 emission reductions of 14-45 GtCO 2 by 2030. Uncertainty ranges depend on the depth and duration of the economic downturn and demand-side changes. Recovering from the pandemic with energy-efficient practices embedded in new patterns of travel, work, consumption and production reduces climate mitigation challenges. A low energy demand recovery reduces carbon prices for a 1.5 °C-consistent pathway by 19%, lowers energy supply investments until 2030 by US$1.8 trillion and softens the pressure to rapidly upscale renewable energy technologies.