Reaching net zero emissions by mid-century was never considered an easy ride given the radical transformation of society required. But three renowned scientists alert that "the emperor has no clothes": gambling on the development of hypothetical carbon sinks to compensate for the continuation of greenhouse gas emissions is in their eyes a fatal mistake. To keep people safe, "large and sustained cuts" to carbon emissions can no longer be delayed. They need to happen quickly and decisively.
The issue. In a landmark article in The Conversation last week, James Dyke, senior lecturer in global systems at the University of Exeter, Robert Watson emeritus professor in environmental sciences at the University of East Anglia, and Wolfgang Knorr, senior research scientist in physical geography and ecosystem science at Lund University, confess:
‘Sometimes realisation comes in a blinding flash. Collectively we three authors of this article must have spent more than 80 years thinking about climate change. Why has it taken us so long to speak out about the obvious dangers of the concept of net zero? In our defence, the premise of net zero is deceptively simple – and we admit that it deceived us.’
Along with other scientists, the authors consider that the current maths of climate stabilisation don't work, and that “it is time to be honest with wider society”. To avoid catastrophe, absolute CO2 reductions need to be prioritised, and we should not rely on fantasised carbon removals that are increasingly unlikely.
Watson, chair of the Intergovernmental Panel for Biodiversity and Ecosystem Services (IPBES) and former chair of the Intergovermental Panel on Climate Change (IPCC), reinforces this point:
‘Relying on untested carbon dioxide removal techniques to achieve the Paris targets when we have the technologies to transition away from fossil fuels today is plain wrong and food hardy. Why are we willing to gamble the lives and livelihoods of millions of people (…) and the future of our children?
Why it matters: a serious overshoot problem. States are often criticised for not respecting the targets they have committed to nor implementing the radical transformation steps required to keep the world “well below 2C” as stated in the Paris Agreement. But on this occasion, it is a critical assumption of the modelling behind the Paris Agreement that is under question.
Indeed, the consensus today is that if fossil fuels are reduced at the same time as “carbon dioxide removal” techniques are deployed, global warming can be halted by mid-century. At that point, any residual emissions of greenhouse gases will not only be balanced by nature-based solutions or technologies removing them from the atmosphere, but so-called negative emissions will even allow a drawdown. A bit like in a fairy tale, pluses and minuses happily compensate each other to avoid the worst effects.
The chart below summarises the net zero pathway, highlighting the role human carbon removal techniques are expected to play from 2025 onwards, whether through human engineering or land sinks (in yellow and orange).
International climate policy has always been a compromise between scientific analysis, climatic and economic modelling, and political decision-making. Based on that logic, the Paris Agreement was cheerfully signed in 2015 and a majority of countries and an increasing number of cities and big companies have since adopted net zero targets, including various forms of offsetting.
What this means is that even if all the Paris targets were respected, the world allows itself to largely “overshoot” the 1.5 C temperature increase threshold. It places an enormous bet on (non-existing) human-induced carbon sinks that are expected in the future to absorb a large portion of the emissions previously released. Under this scheme, it will be necessary within a few decades to magically transform our civilisation from one that currently injects 40 billion tons of carbon dioxide into the atmosphere each year, to one that produces a net removal of tens of billions.
According to the authors, this won’t work out. A “pandora’s box” has in fact been opened by including carbon sinks in climate-economic models :
‘The idea of net zero has licensed a recklessly cavalier “burn now, pay later” approach which has seen carbon emissions continue to soar. It has also hastened the destruction of the natural world by increasing deforestation today, and greatly increases the risk of further devastation in the future.”
Rather than stabilise, global emissions of carbon dioxide have increased by more than 60 per cent since 1992. And with a fast dwindling “carbon budget” for 1.5 to 2 C, the prospect of counting afforestation and carbon capture and storage within the models has given policy makers a way out of making the much-needed cuts to greenhouse gas emissions in time. Carbon sinks conveniently fill the gaps in net zero scenarios and relieve part of the pressure off the reduction of fossil fuels and of the energy demand that is necessary to meet the Paris targets.
Carbon dreams… and reality. While the authors consider there will be some small role for a number of different carbon dioxide removal approaches, the problem comes when it is assumed that these can be deployed at scale. Let’s take a look at some of these different technologies:
- Bioenergy Carbon Capture and Storage, or BECCS, promises that by planting trees and other crops and storing underground the carbon dioxide released and captured when they are burnt, more carbon could be removed from the atmosphere.
But BECCS at scale would require massive planting schemes for trees - mainly monoculture - and bioenergy crops. It has been estimated that it would demand between 25 per cent to 80 per cent of all the land currently under cultivation. Dyke, Watson and Knorr ask how would that be achieved at the same time as feeding 8 to 10 billion people around the middle of the century or without destroying native vegetation and biodiversity.
On tree-planting potential, other scientists have analysed that the maximum amount of vegetation all land on Earth could hold would only sequester enough carbon to offset about ten years of greenhouse gas emissions at current rates. After that, there could be no further increase in carbon capture. They call to refrain from establishing forests where they naturally don’t belong, and avoid “perverse incentives” to cut down existing forests in order to plant new trees.
‘Viewing natural ecosystems as “climate solutions” gives the misleading impression that forests can function like an infinitely absorbent mop to clean up the ever increasing flood of human caused CO₂ emissions’ (Bonnie Waring, senior lecturer in natural sciencies at The Grantham Institute for Climate Change, Imperial College London).
Direct air capture, another carbon removal technique, is still in an experimental phase and suffers at the moment from “exorbitant costs and energy demand”, as Dyke, Watson and Knorr point out. The authors clearly doubt it could be expanded to the levels required and compete economically.
Geoengineering, a deliberate and large scale intervention in the Earth’s climate system, for example, by spraying sulphuric acid in the atmosphere to reflect the Sun’s rays, is gaining traction in some US research and policy circles and would be adding a high-risk gamble on top of another to limit temperature increases. With its massive long-term implications, it should be viewed as a last resort, no return solution rather than a genuine policy option.
From scientific doubts to denouncing false dawns. In an uncommon way, the authors question the attitude of their own scientific community that “expresses doubts in private about the Paris Agreement, carbon capture, offsetting, geoengineering” but “continues to participate in the fantasy of net zero”.
Many consider the world to be heading beyond 3°C by the end of this century, notably because of the fragile assumptions on carbon sink development integrated in the model. In a damning examination of their own responsibilities, they conclude:
‘When it comes to perhaps the greatest challenge humanity faces, we often show a dangerous lack of critical analysis. (…) The price to pay for our cowardice: having to keep our mouths shut about the ever growing absurdity of the required planetary-scale carbon dioxide removal.(…) Current net zero policies will not keep warming to within 1.5°C because they were never intended to. They were and still are driven by a need to protect business as usual, not the climate.’
The bottom line. Such transparent and direct messaging by prominent scientists is rare, and though the argument is not fully new, their forceful demonstration deserves both light and attention. The scenarios we are facing could be much narrower than we like to believe.
At the end of the day, what Dyke, Watson and Knorr have to share is crystal clear: there is no silver bullet on the horizon. They appeal to our intelligence and conscience to stop the daydreaming and face the facts: only absolute reductions of greenhouse gas emissions by every responsible stakeholder in society will now make a difference.