Anticipating the effects of a +4 deg. C global warming: what are the costs of adaptation?

Assessing the economic implications of climate policies is essential for steering public action. Significant progress has been made in assessing the costs of mitigation, with the publication in 2023 of the report on the economic implications of climate action. But as the French Court of Auditors points out in its 2024 annual public report, the issues surrounding adaptation are still much more emerging. Our recent work has nevertheless enabled us to draw 5 initial conclusions on this subject: 1 - Some figures available, but no single cost for adaptation in France; 2 - Without a more ambitious adaptation policy, the spontaneous reactions observed are often the most costly for public finances, and already account for several billion euros a year; 3 - Anticipation options are well identified and could be better deployed; 4 - Among anticipation options, some produce sufficient economic co-benefits to be intrinsically profitable, but not all of them; 5 - In all cases, to ensure the best possible efficiency and distribution of expenditure, adaptation must be integrated into existing planning processes