Balancing a budget or running a deficit? The offset regime of carbon removal and solar geoengineering under a carbon budget

In this new article, published today in the journal Climatic Change, my colleagues Shin Asayama and Nils Markusson and I examine a paradox of adopting a carbon budget as a policy tool. The very idea of a finite carbon budget suggests a decisive focus on controlling carbon emissions to stop global warming. This would seem to marginalise solar geoengineering as a relevant policy tool. But at same time, the more precise the calculation of the remaining budget, creates the political condition in which missing a temperature target would be a high-stakes political failure. Under such circumstances, the danger is that SRM can emerge as a last resort intervention to avoid policy failure. The paradox is that the more transparency science brings into politics, the greater the political risk of failure becomes.


The idea of the carbon budget is a powerful conceptual tool to define and quantify the climate challenge. Whilst scientists present the carbon budget as the geophysical foundation for global net-zero targets, the financial metaphor of a budget implies figuratively the existence of a ‘budget manager’ who oversees the budget balance. Using this fictive character of budget manager as a heuristic device, the paper analyses the roles of carbon dioxide removal (CDR) and solar radiation management (SRM) under a carbon budget. We argue that both CDR and SRM can be understood as ‘technologies of offset’. CDR offsets positive carbon emissions by negative emissions, whereas SRM offsets the warming from positive greenhouse gas forcing by the induced cooling from negative forcing. These offset technologies serve as flexible budgeting tools in two different strategies for budget management: they offer the promise of achieving a balanced budget, but also introduce the possibility for running a budget deficit. The lure of offsetting rests on the flexibility of keeping up an ‘appearance’ of delivering a given budget whilst at the same time easing budget constraints for a certain period of time. The political side-effect of offsetting is to change the stringency of budgetary constraints from being regulated by geophysics to being adjustable by human discretion. As a result, a budget deficit can be normalised as an acceptable fiscal condition. We suggest that the behavioural tendency of policymakers to avoid blame could lead them to resort to using offset technologies to circumvent the admission of failure to secure a given temperature target.