No, don’t do it!

Glen Peters warns about over-reliance on forest carbon sinks in climate mitigation – and climate accounting.

Key points:

  • Warning to the EU: Including forest uptake in the 2030 and 2050 climate targets is a double-edged sword – if asked, he would have urged the EU not to do it, says Glen Peters.
  • Growth in forests is enhanced due to climate feedback (CO2 fertilisation): This means the more we succeed in climate policy, the more the forest sink will decrease.
  • We are at risk of misinterpreting forest carbon dynamics: Forests are possibly transitioning from carbon sinks to sources due to environmental stressors like bark beetle attacks, drought, and wildfires.

Forests represent our most efficient method of capturing carbon on land. They have already saved us from some of the effects of global warming, and if we manage to preserve them, they can continue to aid us in the future.

A conversation with:


Glen Peters is senior researcher in the Climate Mitigation group at CICERO Center for International Climate Research.

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However, forest absorption is declining in many parts of the world, including the EU, where forest uptake is now factored into the climate target. Effectively being deducted from emissions from all sectors. The idea is, in part, that a unified target covering the entire economy is simpler to manage and that it will incentivize countries with extensive forests to conserve them.

But is this really wise? How should we approach and calculate forest absorption? One of those who frequently analyzes the impact of forests on our climate is Glen Peters from Cicero.

– Why is there seemingly so much disagreement on how to account for emissions and uptake in the LULUCF sector?

– It’s a complex issue. Fossil emissions, in contrast, are easy to conceptualise. There are emissions from burning fossil fuels, done.

The LULUCF sector is more complicated. You have land use change, afforestation, or deforestation, where the level of human involvement varies. If I cut down a tree or plant a tree, that is pretty clearly anthropogenic action. But if you are a farmer and one day decide to leave for the city, and then the land turns back into a forest naturally, that could also be called afforestation or reforestation. But is it a result of anthropogenic action?

And with land that remains the same type of land it gets even more complicated and controversial: Forest remaining forest is the most difficult. What happens if an existing forest takes up more carbon simply because we emit more carbon dioxide?

The forest sink

– Which is more important in the big picture? Land use change, or land that remains the same type?

– If you look at a Norway’s or the EU’s emissions inventory, there is a small component which is land use change, afforestation, and deforestation. And a big component which is forest remaining forest. Norway roughly removes 20 million tonnes of CO₂ per year in its LULUCF sector that is dominated by forest remaining forest. Same in Europe, it is about 300 million tonnes or that order. A lot of that comes from the Nordic countries, Sweden, Finland and so on.

– This is the CO₂ uptake in the sector that people want to account in?

– And this has always been a little bit controversial. During the Kyoto protocol negotiations many countries were concerned that others would use their forest uptake to offset their fossil emissions. E.g., that Norway could use its 20 million tonnes of removals in its forests to partly offset its 50 million tonnes of emissions.

Because of that, they made up these complex accounting rules. The idea is you report all your emissions and removals, but you can only account for some of the removals, like afforestation or deforestation, in your climate targets. You can only to a limited degree include forests remaining forests, and only on managed land.

However, he definition of “managed land” is “where human intervention and practices have been applied to perform production, ecological or social functions”. There is some ambiguity and room for interpretation there. If I go look at a forest with my friends and we say, “that’s pretty”, is that a social function and therefore ‘managed’?

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New EU rules

– But, these complex accounting rules … the EU has decided to simplify things a bit there? And put more of the forest uptake on the books?

– In 2021, when revising their climate targets, the EU decided that it would use its entire LULUCF sector as an offset. The 2030 and 2050 targets now include all forests remaining forests in the EU. That means they have roughly 300 million tonnes of removals, and if they can maintain that to 2050, it is a big help to get to net zero. It also changes the 2030-target a little bit. But this is a bit of a double-edged sword from an accounting perspective.

– We will get to that, but first: Does it add up from a climate science perspective?

– If they had asked most climate scientists, they would be saying “no, don’t do it!”.

The problem is that this forest-remaining-forest-uptake is partially due to forest regrowth and partly due to a climate feedback. For every tonne of CO₂ emitted globally, around a quarter is taken up in the ocean, and a quarter is taken up on land. This land uptake is essentially CO₂ fertilisation, something that is treated as a feedback in the climate system (a good feedback). Other factors play a role, like changing temperature and precipitation, the age structure of the forest, and forest recovering from previous disturbances. The 20 million tonnes of uptake in Norwegian managed forests that I mentioned previously, that is a mix of factors like CO₂ fertilisation and tree planting after the second world war.

An “accounting freebie” from destroying the planet

– Hang on. Even if emissions are reduced, the CO₂ concentration will remain high, above 400 ppm for a while, won’t it? If CO₂ fertilization is a function of concentration, will it not remain constant?

– Not quite. At net zero CO₂ emissions, the CO₂ concentration will slowly start declining, but this is largely offset by a continued energy balance, leaving the temperature roughly constant for decades and even centuries. The declining CO₂ concentration means that the CO₂ fertilisation effect will also decline. So, all else being equal, if your emissions go to zero, this feedback essentially goes away. In other words, the carbon uptake we see today is quite dependent on emissions that occurred earlier.

Deforestation is not a feedback, that is human activity. But the uptake of excess CO₂ in managed forests due to CO₂ fertilisation is a feedback that exists because of our historical and current emissions. Therefore, it makes a lot of sense to separate them, because one is a feedback and the other isn’t.

So that is the big picture. We have anthropogenic emissions from fossil fuels, land use change and deforestation, and uptake from remaining forest land, which is largely CO₂ fertilisation, which is essentially an “accounting freebie” that countries can claim because we are destroying the planet.

Deducting uptake now leads to tougher mitigation later

– Is this why you mentioned that from an accounting perspective it was a “double-edged sword”?

– Yes. Say you have 50 million tonnes of emissions, and you remove 20 million tonnes in a sink. There is a perception that you are making your job easier, that you now have only got 30 million tonnes to take care of.

But it doesn’t really change anything at the end of the day. On the contrary, the harder you mitigate, the more you lose your land sink as CO₂ fertilisation gets weaker. And then you might have to mitigate even harder later to compensate. The end point is really the same, but the perceived pathway there changes.

Also, the sink can be reduced further for several other reasons. Droughts, increased bark beetles, fires and foresters wanting to cut down ever more trees can decrease the sink. We are already seeing these issues in Norway, Sweden, and Finland that the land sink is actually decreasing quite substantially. According to some colleagues, it could be gone entirely in Europe by 2030.

If you decide to use the land in your target, and you can’t maintain your sink, you are making the job much harder. The irony here is that those using this “accounting trick” to seemingly avoid emission cuts, are, without knowing it, probably indirectly proposing stronger emission cuts than current ones. Imagine if Norway had forests that took up 20 million tonnes a year like today, and then, ten years later, the same area was emitting 20 million tonnes because of climate impacts and bad management decisions. Norway would have to reduce its fossil emissions by an additional 40 million tonnes (20+20) to compensate for that for the sink becoming a source.

The Czech case: The forest as a net carbon source

– Could these forests become an emission source?

– Yes. A great example is in the Czech Republic, with the bark beetles, their forests have gone from a sink of about 5 million tonnes a year to a source of about 10 million tonnes. In just five years.

There is a link here to forestry in Norway and the “should we count forests like the EU”-debate: Say if Norway is taking up a constant 20 million tonnes in the LULUCF-sector a year, and then decides to increase the harvest. If you harvest more, you expect less carbon uptake in the short-term, something less than 20 million tonnes. But there is a forestry argument that over a long time, when the forest regrows, you generate younger trees that eventually take up more carbon. According to the foresters, the short-term drop in carbon uptake is more than offset by the long-term effect of more carbon uptake in the decades ahead.

But for that to happen, many things need to fall into place. First, the effect is very subtle in the figures they are showing. It depends a lot on how the harvest is used, forest products or bioenergy. Second, forestry models often do not include changes in CO₂ fertilisation or increases in climate impacts. It is what is called a forest inventory model that assumes fixed growth curves. In practice, a drought comes, some bark beetles, a little too much is harvested, and what used to be a healthy carbon sink could be a carbon source. You simply cannot guarantee that the sink is going to behave the way you think it will in a model.

The slippery slope

– So better to just count and report, but keep it off the books?

– Yes. Although you could argue convincingly in both ways. The EU says we can keep managed land on our books, but hands off unmanaged land. Having the managed land on the books may incentivise countries to protect it. But, in Europe, there is basically no unmanaged land. In Canada and Russia, there are significant amounts of unmanaged land. There are those who argue that you should be required to report emissions on unmanaged land also.

I agree, countries should report carbon fluxes on unmanaged land as well. But the slippery slope is when countries start to use that on the books like Europe did with its managed lands. Canada could just start to decide, well, we’ll start to use our managed and unmanaged land on our books. It would be a huge carbon sink if it did that. Some countries already claim they are carbon neutral, because they have forests sucking up carbon. We could easily end up in a situation where the entire land sink is on the books as carbon dioxide removal. If Europe can do it, why can’t Brazil or Democratic Republic of the Congo?

The global land sink would offset about 25% of global emissions. The idea to include it on the books is that countries will feel obliged to manage it. That is in principle a good incentive, unless it is used to offset fossil emissions and not solve the climate problem. A better strategy is to keep fossil and LULUCF emissions separate, with separate targets and incentives. The EU does this to a degree, where LULUCF emissions have a separate target but is still used to offset fossil emissions.

– And finally, part of the problem with this is also that there is no universal method of accounting for this sector?

– Yes, there is no consistent methodology to estimate the emissions from managed lands. It is a quagmire. So it is a bit easy to get carried away with the managed land that countries report and overinterpret it, because every country does it differently. It is not helpful knowing that you have 40 countries reporting on these emissions when they employ 40 different methods and get results that are not comparable.