Refining the budget: limits of the cumulative emissions framework and implications for policy

The linear relationship between cumulative emissions and warming has been a consistent feature of climate models, and underpins the concept of a carbon budget and net-zero goal in order to achieve climate stabilisation.  However, research in recent years has identified potential for deviations from this relationship during the net zero transition.  Here, we consider how important such deviations might be for achieving the goals of the Paris Agreement, and whether current metrics of Earth system warming in response to carbon emissions (TCRE, ZEC, RAZE) adequately describe the range of potential warming trajectories which might be experienced in response to different levels of mitigation.  Further, as carbon emissions (hopefully) peak and decline in the coming decades, we examine the prospects for further constraining response parameters as temperatures depart from the linear growth seen over recent decades.  Finally, we consider how the current CMIP experimental protocol could be extended to better define transient response to real world emissions in a net-zero transition.