What is a carbon budget? It is a target for carbon reduction. The government has decreed the UK must cut greenhouse gas emissions by 34 per cent by 2020. That breaks down into three shorter-term targets: by 2012, a 22 per cent cut is required; by 2017, a 28 per cent cut; and by 2022, a 34 per cent cut.

Is the target for 2020 or 2022? Both. Technically the third Budget period ends in 2022 but the government prefers to use 2020 as the date to align with international goals.