Reducing greenhouse gas emissions alone cannot save the world from the worst ravages of climate change, a report by UN experts released on Monday is expected to underline. In addition, it will be necessary to resort to techniques for the “elimination” of CO2.
For lack of effort so far, global emissions must be reduced by 5 or 6% per year to hope to meet the Paris Agreement objective of limiting global warming to “well below” 2°C compared to the pre-industrial level, even more for 1.5°C.
To get an idea, during the shutdown of the global economy linked to COVID-19 in 2020, the drop in CO2 reached “only” 5.6%, before rising again. Hence the need for the use of carbon dioxide removal (EDC) or “negative emissions” techniques.
“For the EDC to work, we must (already) reduce greenhouse gas emissions by 80 or 90%”, estimates Glen Peters, of the International Center for Climate Research in Oslo.
Even if humanity managed to do this, there would still be several billion tons of CO2 to be extracted from the atmosphere each year by 2050.
EDC will also be essential for sectors unlikely to be able to decarbonise by 2050, such as aviation, maritime transport or cement manufacturers, and will be necessary to cool the atmosphere if warming exceeds the objectives of the Paris agreement.
Currently, EDC techniques are very far from the required efficiency. The largest direct air capture installation in the world thus eliminates in one year what humanity emits in three or four seconds.
There are at least a dozen techniques, with varying potentials and costs, according to benchmark studies likely to be cited in Monday’s Intergovernmental Panel on Climate Change (IPCC) report, which will focus on solutions to climate change.
Bioenergy with capture
Bioenergy with carbon dioxide capture and storage involves growing trees that absorb CO2 during their growth, then burning them in order to produce energy (biomass) and to bury the CO2 resulting from this combustion, in abandoned mines for example. The technique, if it works in theory, has yet to materialize.
One of the few commercial-scale projects in the world, in the UK, has been removed from the S&P Clean Energy stock index after failing sustainability criteria.
To plant trees
Another solution: restore forests and plant trees to absorb and store CO2by photosynthesis.
Many companies, including fossil fuel producers, rely heavily on these plantations to “offset” their emissions.
But the area needed to significantly reduce CO levels2 by planting trees — up to twice the size of India — competes with other priorities, such as growing crops for food. Biodiversity could also suffer.
New forests can also fall victim to fires that multiply with warming, releasing all the CO2 stored.
Direct capture
One of the newest technologies is also one of those attracting the most attention: direct CO capture.2 in the air and its storage.
Chemical processes extract the carbon to convert it into a solid form or bury it. Because CO2 in the air is very diffuse, it is an energy-intensive and expensive process.
Even if these innovative technologies benefit from the attention and the money of big bosses like Elon Musk, they remain very expensive, and uncertainties persist on the speed of development.
crushed rocks
“Augmented weathering” involves mining and crushing mineral-rich rocks that naturally absorb CO2then spreading them on land or at sea. The goal is to accelerate a process that normally takes place on geological time scales of tens of thousands of years.
The big question is whether this can be implemented on a sufficient scale, and at what cost.
The oceans already absorb more than 30% of humanity’s carbon emissions, and scientists are experimenting with ways to increase this capacity, such as artificially boosting marine alkalinity or “fertilizing” the oceans. ie by increasing the density of phytoplankton which produces and sequesters organic carbon by photosynthesis.
The main concerns relate to unintended consequences on ecosystems, as well as the possibility of scaling up this method.