The costs of shifting scenarios: Why the IPCC should maintain consistent vocabulary in climate assessments
The scenarios used in the Intergovernmental Panel on Climate Change (IPCC) reports are critical instruments in our understanding and response to climate change and serve as a scientific foundation for global climate action.
They provide scientifically rigorous, peer-reviewed projections of future climate conditions under different greenhouse gas emission pathways. From the “SA90” (Scenario A from 1990) in the First Assessment Report (AR1) to the Shared Socio-economic Pathway (SSPs) in the Sixth Assessment Report (AR6), these scenarios have evolved in complexity and precision, reflecting our growing understanding of the climate system and the increasing sophistication of modeling techniques to assist public and private sectors on strategic decision, climate change risk assessment and adaptation planning. These scenarios are essential for informing policy because they provide a range of possible futures, each corresponding to specific assumptions about socio-economic development, technological progress, and mitigation efforts. By outlining the potential consequences of different emission trajectories, they enable policymakers to assess the risks and trade-offs associated with their decisions.
Moreover, scenarios help to quantify the impacts of climate change at global, regional, and local levels. They provide crucial data for climate impact assessments, informing strategies for adaptation and resilience building. These scenarios also play a pivotal role in economic analyses of climate change, helping to identify cost-effective mitigation strategies and guiding investments towards low-carbon development and climate change adaptation measures.
Over the course of the past six IPCC assessment cycles, the naming conventions and frameworks for socioeconomic and emissions scenarios have changed. While intended to utilize updated scientific information, this shifting terminology creates significant confusion to national governments, and to sectors who need to incorporate scenarios in their planning and policy makers. Significant challenges are encountered due to lack of knowledge on understanding scenarios, interpretation and transition costs for climate risk assessment using new scenarios and capacity building of national and local stakeholders and legislative changes. Changes of vocabulary could create technical, social, financial, and capacity building challenges. Evidence from past assessments revealed that around USD 200 million was spent in transition costs across IPCC reports due to terminology shifts. This could amplify significantly for countries capacity building, risk assessment and changes in legislations and policies. IPCC should use nuanced scenario vocabulary after AR6 and utilize consistent terms through at least Seventh Assessment Report (AR7), and potentially following assessment cycles in the future.