Net zero is routinely discussed as though it were a slogan, a vibe a government can adopt or drop with a speech. It is neither. It is a line in an Act of Parliament, and understanding what the law actually says explains why the argument keeps returning to the same place regardless of who is in office.
The foundation is the Climate Change Act 2008, which originally required the UK to cut greenhouse gas emissions by 80% against 1990 levels by 2050. In June 2019, after formal advice from the Climate Change Committee, Parliament amended that figure to 100% through a statutory instrument passed without a division. "Net" is doing specific work in the phrase: the Act does not demand zero emissions, but that any emissions remaining in 2050 are balanced by removals, whether trees, restored peatland or engineered capture. The duty sits personally on the Secretary of State, which matters because a named legal duty is something a court can enforce.
Enforcement runs through carbon budgets. Every five years the government must set a legally binding cap on total UK emissions for a five-year period, and it must do so roughly twelve years ahead, so that investment decisions in power stations, vehicle fleets and housing have a fixed horizon. Six budgets are already law. The Sixth, covering 2033 to 2037, requires a 78% cut against 1990 and for the first time counts the UK's share of international aviation and shipping. Advice for the Seventh, covering 2038 to 2042, recommends an 87% reduction. Missing a budget is therefore a breach of statute, not just a political embarrassment to be shrugged off.
The watchdog is the Climate Change Committee, an independent statutory body created by the same Act. It recommends the level of each budget, publishes an annual progress report to Parliament, and the government is legally obliged to respond. Its assessments are unsentimental in both directions: it credits the roughly 50% fall in territorial emissions since 1990, driven overwhelmingly by the collapse of coal-fired electricity, and it states plainly that the remaining half is harder because it lives in heating, transport, farming and industry rather than in a handful of power stations.
The courts have made the duty bite. In 2022 the High Court found the Net Zero Strategy unlawful because ministers had not shown how their policies would actually deliver the budgets, and in 2024 the replacement Carbon Budget Delivery Plan failed on similar grounds. Both rulings forced redrafts. Whatever one thinks of the target, a policy that can be struck down for arithmetic inadequacy is not a gesture.
Where the honest argument actually sits
None of this settles the questions that dominate the public row, because the Act deliberately does not prescribe a pathway. It fixes the destination and the checkpoints; ministers choose the route. That is where the genuine disputes live. How fast should the sale of new petrol and diesel cars end, and does moving the date change manufacturer investment or merely headlines? Should households be pushed towards heat pumps by mandate, subsidy or carbon pricing on gas? How much removal capacity is it prudent to assume in 2050, given that engineered capture barely exists at scale?
Distribution is the second live question. The Committee's own analysis puts the net cost of the transition at well under 1% of GDP a year, lower than earlier estimates because renewable electricity became cheap faster than anyone forecast. But an average conceals who pays: levies currently sit on electricity bills rather than gas, which penalises exactly the switch policy wants; upfront costs of insulation and heat pumps fall on households while savings accrue over decades; and workers in high-carbon industries carry concentrated risk for a diffuse national benefit. These are questions about tax design, obligation dates and compensation, and they deserve a sharper debate than they get.
What the framing of that debate should not do is pretend the duty itself is optional. Repeal would require primary legislation, a Commons majority for it, and the unwinding of the UK's pledge under the Paris Agreement, where its nationally determined contribution promises an 81% cut by 2035. A government could attempt all of that. None has proposed it, including those loudest in complaint, which tells you something. The commitment is real, binding and audited; the choices about speed, sequence and fairness remain open, and they are where the votes and the money actually move.