What does 'net zero emissions' mean?

The concept of net zero greenhouse gas emissions was first popularised by the Paris Agreement, a landmark deal that was agreed at the United Nations Climate Change Conference (COP21) to limit the impact of greenhouse gas emissions. At the watershed meeting, nearly 200 countries agreed “to achieve a balance between anthropogenic emissions by sources by sinks of greenhouse gases in the second half of this century.” In other words, hit net zero emissions by around mid-century.

In 2018 the timeline and need for the goal was spelt out more clearly, by the Intergovernmental Panel on Climate Change’s report on stopping 1.5°C of warming. The UN climate science panel said that global carbon dioxide emissions must fall by about 45 per cent by 2030, and to net zero by 2050, for the world to have a chance of avoiding the devastating consequences of breaching the 1.5°C threshold.

That report helped spur countries including Sweden to set a goal of net zero emissions by 2050, followed by the UK in 2019, the first major economy to do so. In 2020, China, the world’s biggest emitter, pledged it would reach “carbon neutrality” by 2060. Businesses, and sub-national actors such as states and regions, have also set similar targets.

Why net rather than just zero? Even if we decarbonise our electricity grids entirely, make green hydrogen production affordable and dramatically scale up carbon capture and storage, there will still be a rump of emissions left by 2050. Most of those will come from hard- or impossible-to-abate sectors including farming, aviation, some heavy industry and waste.

That is where greenhouse gas removals come in. Tree-planting, restoring peatlands, and technologies such as direct air capture of CO2 can tip the carbon accounting scales to cancel out the remaining rump, leaving a country or business at net zero.

There are a few technical but important questions around the best ways to achieve net zero. One is over whether “carbon credits” from other countries should be allowed to count towards a country’s progress. The UK government’s advisers, the Climate Change Committee (CCC), argues they should not, because of the expense but also because all countries will eventually need to reach net zero, so that option will vanish.

Another is over whether net zero should cover just carbon emissions or all greenhouse gas emissions, including others such as methane, which comes principally from farming and oil and gas production. The CCC says it is better to cover all greenhouse gas emissions.

Some figures, such as former Bank of England governor Mark Carney, have stirred controversy by appearing to suggest alternative definitions of net zero. He claimed the asset manager where he works, Brookfield Asset Management Inc, was net zero because its investments in renewable energy “avoid emissions”, despite the firm holding major investments in coal, oil and gas. Carney later rowed back on the claim.

There is concern in some quarters that companies and countries are “greenwashing” by announcing net zero targets but not putting sufficient action in place to meet them. The UK, for example, made its target law in June 2019 but as of March 2020 is still off-track to meet even its near-term targets for the mid-2020s, let alone long-term net zero by 2050.