The European Commission recently announced it would aim to cut emissions by the bloc by as much as 55% against 1990 levels until the year 2030. The plans have come under fire because they include not only emissions from fossil fuel burning and cement production, but also COâ‚‚ removal by â€œcarbon sinksâ€ like forests or the soil.
Even though the plannedÂ legislationÂ does not specify what is meant by â€œremovalâ€, the possible inclusion of natural carbon sinks has been termed â€œcheatingâ€ byÂ GreenpeaceÂ and â€œgamesâ€ byÂ the WWF. Are these accusations justified?
To understand this, we need to remember that to meet the Paris Agreement target to keep global warming â€œwell below 2Â°Câ€,Â the world has less than 12 yearsÂ ofÂ current COâ‚‚ emissionsÂ until it exhausts its remaining budget. It is now becoming clear that the only way to stay within this budget is toÂ capture and store massive amounts of COâ‚‚.
What is usually overlooked though is that since the beginning of industrialization,Â most of the COâ‚‚ emitted (57%)Â has been taken up by natural processes. In fact, while emissions from fossil fuels, cement production and deforestation have been growing exponentially (atÂ 1.65% per year since 1850), my own research has found that natural sinks on land and in the ocean have been almost exactlyÂ keeping up with the growth.
Processes on land alone are responsible for taking up about a third of human COâ‚‚ emissions. So for every kilo of carbon emitted by a car or a power plant, about 350 grams will end up in a tree trunk, a leaf, or decomposed into the soil. There is no consensus about exactly what is responsible for the growing strength of the land sink, but most likely it is a combination of more COâ‚‚ in the atmosphere and nitrogen-containing chemicals from agriculture and industry ending up on soils and leaves, both of which make plants grow faster, as well as forests regrowing when agricultural lands are abandoned.
The inclusion of a constant EU-wide carbon sink calculated following the EUâ€™s own rules effectively lowers the promised fossil-fuel reduction from 55% to somewhere betweenÂ 53% and 50%.
A subtle form of double accounting
But there is a much more fundamental problem with the Commissionâ€™s approach. It is a subtle form of double accounting that sets a precedent for more significant accounting tricks further down the line â€“ or by other countries with larger land carbon sinks.
The problem is that when scientists calculated how much COâ‚‚ we can emit and still keep within the safe limits of the Paris Agreement, natureâ€™s free carbon sucking service was already included. The net-zero goal is strictly in addition to that. By the time we hit net zero, we actually need those natural sinks to continue functioning, taking up overÂ 22 billion tonnes of COâ‚‚ per yearÂ and continuing to reduce COâ‚‚ levels in the atmosphere below where they ended up at the net-zero point. Because current levels of atmospheric COâ‚‚ areÂ not safe. In other words, the needed net zero really is a â€œbig minusâ€.
How much carbon is stored in EU countries through natural processes is essentially unknown.Â EstimatesÂ vary between 0.6 and 1.7 gigatonnes of COâ‚‚ per year, with no consensus about how much of it is within EU boundaries. Contrary to the global land sink, which can be inferred fromÂ combining COâ‚‚ and oxygen measurements, the European sink cannot be measured directly because these gases mix too quickly in the atmosphere.
But what happens if, at some point in future, the EU produces data that shows its carbon sink has increased? The amount of fossil fuels it would be legally-required to cut would be reduced â€“ but the scientifically-determined global carbon budget to meet the Paris Agreement would remain unchanged. Given what we know about the global land carbon sink, it is likely the EU carbon sink will approximately double between 1990 and 2030.
This is clearly a bad start on the road to net zero as it sets a precedent for double accounting. A possible solution might be to only account for sinks that are genuinely additional, such as planting more trees orÂ no-till farming to increase soil carbon. However there is still no consensus about which processes govern the natural carbon sink, and it is likely to be partly human-induced. It is therefore next to impossible to reliably determine how much of a sink is truly additional.
Another solution could be to allow only direct COâ‚‚ uptake by human activities to be counted as â€œremovalâ€. So-called bioenergy with carbon capture and storage (BECCS) is one option, however it interferes with the biosphereâ€™s capacity to soak up COâ‚‚ as it requiresÂ vast amounts of landÂ to grow biofuel crops (and competes with food production). The other option is to directly capture carbon from the air, but for now this hasÂ limited realistic potential.
By far the most scientific, ethical and sensible approach would be to concentrate on emissions reductions and leave the terrestrial biosphere as intact as possible to carry on removing carbon. This free service, after all, is worth at least US$1.3 trillion per year (at a price of 100 US$/tonne). Natural habitats should be restored for that purpose, but the resulting carbon sink should not enter territorial accounting schemes for two reasons: because it has already been counted, and because we have no way of reliably quantifying how much is down to human policy and how much is just the natural background rate.
This article is republished fromÂ The ConversationÂ byÂ Wolfgang Knorr, Senior Research Scientist, Physical Geography and Ecosystem Science,Â Lund UniversityÂ under a Creative Commons license.