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To understand how global warming can be kept well below 2 degrees Celsius and even 1.5 degrees Celsius, climate policy uses scenarios that describe how society could reduce its greenhouse gas emissions. However, current scenarios have a key weakness: they typically focus on reaching specific climate goals in 2100. This choice may encourage risky pathways that delay action, reach higher-than-acceptable mid-century warming, and rely on net removal of carbon dioxide thereafter to undo their initial shortfall in reductions of emissions. Here we draw on insights from physical science to propose a scenario framework that focuses on capping global warming at a specific maximum level with either temperature stabilization or reversal thereafter. The ambition of climate action until carbon neutrality determines peak warming, and can be followed by a variety of long-term states with different sustainability implications. The approach proposed here closely mirrors the intentions of the United Nations Paris Agreement, and makes questions of intergenerational equity into explicit design choices.
International climate policy aims to prevent dangerous anthropogenic interference with the climate system1. Since about a decade ago, decision makers have been translating this broad objective into more specific temperature limits2. Such temperature goals have limitations, but can serve as proxies for climate effects, at both global and local scales3-5. In 2015, the Paris Agreement concluded many years of negotiation and reset the aim of international climate policy to holding global warming to levels well below 2 °C and pursuing efforts to limit it to 1.5 °C- an objective that in its entirety is referred to as the Paris Agreement's long-term temperature goal6 (LTTG). The Paris Agreement LTTG hence defines an envelope of acceptable climate outcomes, which-it specifies-should be pursued in the broader context of sustainable development7 (see Methods for more background on the LTTG).
Scenarios developed with models of the combined energyeconomy-environment system provide key tools to explore how the future could evolve, and how today's decisions could affect longer-term outcomes8. Over the past decades, researchers have extensively used such scenarios to identify integrated solutions that can limit climate change, and to inform international climate policy8,9. This literature does not cover all possible interpretations of global climate goals with equal detail and depth. The vast majority of scenarios available in the literature either...