We asked the Treasury why, in its updated Green Book, it had not introduced a specific requirement for policies to explain how they aligned with net zero. The Treasury told us that the guidance already required Departments to consider greenhouse gas emissions as part of their appraisal process.24 The NAO found, however, that Departments’ adherence to guidance, including that in the Green Book, was often inconsistent. The Treasury accepted that taking greenhouse emissions into account was “not always happening on a consistent basis” and that it needed to do more to set the expectations of Departments.25 In the most recent spending review, the Treasury asked departments to provide a detailed assessment of the climate impact of their capital expenditure plans, but not all departments did so. It explained that the main issue was the capability of departments, as much of the capability for assessing the climate impact of policies sits within the Department. The Treasury recognised that there was more it could do to ensure departments have the tools and capabilities to assess the climate impact of policies.26 Impact on global emissions