As Greta Thunberg blasted the EU’s climate law “surrender”, she had another important message to broadcast.

“Until we have the technologies that at scale can put our emissions to minus then we must forget about net zero or ‘carbon neutrality’,” the 17-year-old activist wrote in a letter to the bloc’s leaders. “We need real zero.”

The Swede was highlighting an often ignored, but increasingly critical part of Paris Agreement pledges – carbon capture and storage. As the EU celebrated its 2050 net zero target to reduce global warming to 2°C, Ms Thunberg asked how we can possibly continue burning fossil fuels now and defer drastic mitigation until later.

This deferral is seemingly lent legitimacy through negative emission technologies (NETs) – which are included in the majority of 1.5C and 2C pathways by the Intergovernmental Panel on Climate Change (IPCC). The modelling has been interpreted by many policymakers that we can overshoot our dwindling global carbon budget (800Gt until 2100 and counting) if we place faith in untested technologies in the future.

The most prominent of these fixes, bioenergy and carbon capture and storage (BECCS), is besieged by a number of issues, including the sheer land mass required (up to 80 per cent of global cropland). It involves absorbing carbon dioxide through photosynthesis when growing biomass, burning or converting the feed to create power, and sequestering the resulting carbon underground – thus promising the creation of net negative emissions. Other impressive but still underdeveloped methods include directly capturing CO2 from the air before storing it (DACCS), using iron fertilisation to increase oxygen levels in the ocean, or simply planting trees through afforestation and reforestation.

Dr Ajay Gambhir of Imperial College London’s Grantham Institute believes NETs can still have a role in our decarbonised future – but that they can prove a “distraction” from the priority of emissions reductions.

“Over-reliance on NETs, none of which have been demonstrated at commercial scale, is risky, especially if used as an excuse to delay emissions reductions today,” he told The Independent.

“There are several cost-effective ways of doing this which aren’t being taken up, such as closing increasingly unprofitable fossil fuel power plants, energy efficiency measures, dietary changes and less profligate consumption. In this sense, NETs are a distraction.”

While BECCS may be the technology most favoured in IPCC pathways, it can currently be found in only one pilot plant at Drax in Selby, where one ton of carbon a day is removed (there are four other plants in operation worldwide). A Drax spokesperson said the technology would have the potential to store 16 million tonnes of carbon a year by 2035 – and that by 2050 BECCS could generate up to 173TWh of electricity by 2050, capturing up to 51 million tonnes of CO2 – around half of the remaining carbon in the economy that the UK will need to capture to become net zero.

The word “potential” has alarm bells ringing for scientists. Professor Simon Lewis, Professor of Global Change Science at University College London, says there is a role for negative emissions technologies – but they should not be considered an excuse for policymakers to continue with “business as usual”.

“These technologies must be in addition to getting emissions down as much as possible and as fast as possible,” he told The Independent.

 “Negative emissions technologies are essential to mop up residual emissions and reach net zero, but it is delusional to consider them as a way of allowing for the continued use of large amounts of fossil fuels.”

The Department for Business, Energy and Industrial Strategy has been contacted for a comment.

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