Prof Duncan McLaren is a research fellow at Lancaster University’s Lancaster Environment Centre

The UK and several other countries now aim to deliver “net-zero” greenhouse gas (GHG) emissions by 2050, broadly in line with advice from the Intergovernmental Panel on Climate Change (IPCC).

Both the IPCC and the UK’s Climate Change Committee have also highlighted the likely need for negative emissions, in addition to increased efforts to cut greenhouse gas outputs, if emissions are to fall to ‘net-zero’.

However, our newly published research – based on findings from expert interviews and stakeholder deliberations – suggests that combining emissions reductions and negative emissions into a single target of reaching “net-zero” may create problems. These could include delayed emissions cuts, but also insufficient focus on developing negative emissions technologies.

Here, we explain how these problems arise and suggest one possible solution.

Target interactions

A net-zero target contains within it two related, but different responses to the problem of rising temperatures. The first is to stop releasing GHGs in the first place, by cutting emissions. The second is to remove CO2 from the atmosphere using “negative emissions technologies” (NETs).

A net-zero target is met when these two balance – when residual emissions are offset by CO2 removals. The problems lie in the interaction between these two. If we pay more attention to removals, how might that affect releases?

Even if negative emissions simply substitute for feasible emissions reductions, there could be negative side-effects. Unlike carbon emissions prevented by mitigation, carbon put into forests, soils or even geological stores could leak back into the atmosphere. And NETs may bring other environmental or social risks, such as heightened competition for land.

But the main problem is that most NETs are still only prospective technologies – they do not exist as large-scale socio-technical systems ready for deployment. Our stakeholder workshops highlighted huge uncertainties in how – or in some cases, whether – different NETs might work technically, economically and politically.

Net-zero plans that rely on promises of future carbon removal – instead of reducing emissions now – are, therefore, placing a risky bet. If the technologies anticipated to remove huge quantities of carbon in the 2040s and 2050s fail to work as expected – or lead to rebounds in emissions from land-use change, for example – then it might not be practical to compensate for the cumulative emissions from mitigation foregone between now and then.

Ironically, researching or investing in carbon removal techniques in an effort to reduce technical uncertainties might heighten expectations of future removals. And such expectations were identified by participants in our research as an important possible factor that could undermine efforts to accelerate mitigation now, through their effects on pathway modelling or carbon markets.

Historic myopia

NETs have been included in climate modelling and policy pathways for many years, but have not generally been clearly signposted. Their growing role has often remained hidden within charts showing falling emissions, until after 2050, when overall emissions become net-negative.

The experts we interviewed – our deliberations and interviews involved 80 people from the worlds of policy, business, academia and NGOs – suggested that this problem both obscured the need to start developing NETs and distracted attention from the tendency of the models to deploy extremely high levels of future negative emissions – from technologies such as bioenergy with carbon capture and storage (BECCS) – which may not be practically or sustainably deliverable.

As tools for policy development, those same model pathways – which involved slower emissions reductions when NETs were included – are seen by some as having provided new excuses for continued delays in mitigation.

In part this is because the future negative emissions can appear cheaper than accelerated mitigation, because their costs get discounted over the intervening decades. These “integrated assessment models”, therefore, tend to replace near-future emissions cuts with distant-future negative emissions.

In some cases, negative emissions have already substituted for emissions reductions, instead of supplementing them. For example, many forest protection projects would have happened anyway. But when such carbon sink enhancements – a form of negative emissions – are traded as offsets in carbon markets, this means emissions get to continue elsewhere, instead of being cut.

While deployment of NETs as offsets, or as carbon utilisation means that emissions continue – either elsewhere, or at the end of life of the carbon utilisation product – it could still be useful. It might help developers improve the technologies and capture economies of scale and of learning, making them more commercially viable for future removals.

But – as Jesse Goldstein at Virginia Commonwealth University has demonstrated for “cleantech” generally – such deployments also imply specific technological forms, enabling investments and regulatory regimes which, in this case, risk locking-in applications of the technology that sustain or encourage fossil fuel use.

One example is the way that many of the very limited number of BECCS developments so far provide CO2 for enhanced oil recovery, creating more emissions.

Meanwhile, some businesses are setting “net-zero” corporate goals involving negative emissions “offsets”. For example, Heathrow pays for peat-bog restoration as an offset to contribute to “carbon neutrality” in airport operations, while oil major ENI has promised expansive afforestation to offset its operational emissions. Such goals help legitimise continued aviation and fossil fuel extraction.

Ensuring additionality

If negative emissions are necessary for net-zero, but also uncertain, it would seem crucial to ensure that they are delivered in addition to rapid emissions reduction, rather than risking that they might slow it down.

How can we design policy to get both? One potential mechanism, emerging from discussions in our deliberative workshops, would be to insist on formal separation of negative emissions targets and accounting for emissions reduction, rather than combining them in a single “net-zero” goal.

“Net-zero” has only recently become widespread and mainstream, and its introduction was in part an important effort to bring more clarity to the debate. The idea of separation seeks to build on that aim, while avoiding the potential loopholes “net-zero” might otherwise create.

Explicitly setting and managing targets and accounting for negative emissions, separately from existing and future targets for emissions reduction, at all levels from international to sectoral, could help to address the problems outlined above, maximising the additionality of carbon removal and ensuring that negative emissions are appropriately valued.

Separation would have implications for climate target definition; offsets and carbon trading; incentives; and modelling and evaluation processes.

First, in target setting, the separation approach would call for explicit separate objectives and timetables for emissions reduction and negative emissions. Moreover, “net-zero” would no longer be the ultimate end-goal, but instead, a critical stepping-stone: at least some sectors or countries would need to deliver net-negative emissions if atmospheric CO2 concentrations are to be reduced to safe levels.

For example, agriculture could contribute significantly to net-negative emissions through soil carbon storage or enhanced weathering. But if these negative emissions were simply used to “net-off” the impacts of continued high meat production, then the emissions benefits of shifting diets might never be realised and the potential of agriculture to contribute to actively drawing down atmospheric GHG concentrations would be lost.

Similar issues are raised by states that plan to deliver net-zero emissions via the purchase of international offsets, rather than by transforming consumption habits or reducing oil production.

Second, formal separation would also imply developing clear rules for negative emissions in offsetting and carbon trading systems. Removing or excluding negative emissions from carbon markets would be the simplest response.

In theory, although this might reduce the incentives for negative emissions, avoiding offsetting between removal and emissions cuts should push carbon prices higher in emissions trading markets, stimulating more rapid decarbonisation.

Third, separation highlights the need for appropriate financial incentives for negative emissions, rather than relying on a general carbon price. Energy market experience with renewables suggests that there is more public support for targeted mandates and incentives than for carbon pricing – and that this can favour more context-specific portfolios of appropriate technologies.

In the case of NETs, such an approach might mandate increasing levels of long-term carbon storage, encourage research into novel technologies and also support the immediate deployment of existing “nature-based” carbon removal approaches.

Finally, the separation approach implies differences in evaluation and assessment methods, in particular, revised approaches to integrated assessment modelling that are explicit in how they handle and incorporate NETs, and their interactions with emissions reductions.

Ideally, such models should not treat NETs and emissions reductions as interchangeable, as they do now. But relatively minor adjustments – for instance, using lower discount rates or simply reframing scenario design – could significantly curtail the tendency of these models to substitute distant future NETs for near-term emissions reductions.

The separation approach would also increase clarity about the residual emissions allowed within a net-zero goal, facilitating debate about whether such emissions were truly recalcitrant. Perhaps more importantly, it could also highlight those countries or groups that get the benefits of residual emissions. In this way separation could contribute to climate justice.

Exposing interests

In questioning “net-zero” we mainly seek to highlight possible downsides and reframe the challenge to avoid the possible shortcomings of net-zero narratives and approaches.

Clear separation would expose interests and politics, meaning deliberate efforts to substitute negative emissions for emissions reduction could not be hidden behind net-zero rhetoric. In addition, the justice implications of who generates residual emissions would become clearer.

Separation might also be expected to reveal where negative emissions investment and development is inadequate, as well as where negative emissions – or future promises thereof – could undermine or deter emissions reduction.

In questioning net-zero, however, we also want to ensure that it is not seen as the last word in targets. Even if emissions were brought to net-zero by 2050, the world would likely still need to achieve “net-negative” emissions for a period, to reduce atmospheric CO2 concentrations back to safer levels. At least some countries and sectors will need to go “beyond net-zero”.