Methodology for calculating net negative emissions from carbon capture and storage depends on the purpose  

On February 10, The Norwegian Environment Ministry presented their report “Klimatiltak i Norge 2026: Veivalg og utslippsbaner mot 2050” (Climate measures in Norway 2026: Strategic choices and emissions pathways towards 2050). The biggest news of the report was that it is possible for Norway to cut emissions by more than 90 per cent by 2050.

"These require powerful measures in all sectors," says Hilde Singsaas, the director of the agency in their press release about the report.

One of the most important measures highlighted in the report is carbon capture and storage (CCS). This is the measure that has the potential to cut emissions most significantly, writes NRK. The reason is, among other things, that the technology might be able to produce net negative emissions in the future, according to Minister of climate and environment, Andreas Bjelland Eriksen.

“It could give us a little more room to manoeuvre”, says Eriksen to NRK.

The purpose decides the method

To realise this potential, we need reliable methods to document that the climate measures actually remove more climate emissions from the atmosphere than they release.

"Clear, comprehensive and consistent accounting rules would enable the voluntary carbon market (VCM) to play a vital role in funding projects that support countries in meeting their Net-Zero Emissions targets," writes NORSUS researchers Hanne Lerche Raadal and Ingunn Saur Modahl in the report "Methodology for documenting negative emissions and Carbon Dioxide Removals (CDRs) applied for different intended purposes – Based on a Waste to Energy (WtE) BECCS case".

The researchers have assessed methodology to calculate and document negative emissions. The methodology is based on life cycle assessments (LCA) – a recommended method to assess if carbon dioxide removals (CDR) actually deliver real climate benefits.

• Read more: About Life cycle assessments

By looking at the whole value chain, from the moment carbon dioxide (CO₂) is captured at a facility, via transport, until it is stored permanently, we are able to get a real calculation of whether the result is “net negative”. In other words, that the climate emissions are removed from the atmosphere, and not that the system simply emits less than other options.

Investigating waste incineration with carbon capture

The researchers have looked at waste incineration with carbon capture (BioEnergy with Carbon Capture and Storage – BECCS) as an example. In this process the captured CO₂ origins from biological material. These materials, for example plants, contain CO₂ that is captured by the plants themselves while they are growing.

When the CO₂ from the plants, by the process of CCS, is led down into the ground for permanent storage instead of being released into the atmosphere, the system can be credited for actually removing CO₂ from the atmosphere.

If, on the other hand, the technical steps of the capture itself create more climate emissions than the amount being permanently stored, the process does not result in net negative emissions.

And this is where LCA enters the picture. The methodology captures all emissions throughout the entire life cycle – from the material is produced, until the CO₂ is permanently stored.

The NORSUS-report shows that for a typical CCS value chain there is a need to subtract emissions originating from transport, chemical production, and energy used to capture the CO₂, to find the actual climate reductions.

Fact box: When a tree falls in the woods, where no one can hear it, do we then calculate the emissions immediately?

The report presents two ways of calculating emissions of biogenic CO₂ (CO₂ that has been captured by trees and plants): “0/0” and “-1/+1”.

The biogenic and the fossil CO₂ cycle differ by their turnover time: if we take a tree that is decomposed or burned as an example, it releases CO₂ that was recently removed from the atmosphere during photosynthesis. In contrast to fossil fuels, which release CO2 captured thousands of years ago, no new CO₂ is added to the atmosphere when biogenic matter is decomposed.

The question researchers ask themselves when calculating emissions from biological materials is whether to allow uptake and emissions to cancel each other out immediately, even if it might take a while for the tree to emit the captured CO₂ (through for example natural decomposition), or if the calculation should include the actual uptake of CO₂ (-1) when the plant is growing, and the emission when the plant is burned or decomposed (+1).

Both methods give the same net results for the accounting, but -1/+1 shows more clearly where in the value chain the CO₂ is actually being removed and released.

Different methodologies for different purposes

In addition to showing how to use LCA to calculate and document the negative emissions from a CCS facility for waste incineration, the main message in the report is that the purpose of the documentation decides the best way to calculate the benefits and burdens of the value chain.

The report separates between three main purposes:

1. Technical documentation: To prove if the technology actually delivers negative emissions across the entire value chain.
2. The voluntary carbon market: To generate credible carbon removal credits that companies can buy to neutralise their own emissions.
3. National climate accounting: To report emission reductions by sector for governmental and international reporting. It is expected that this, in time, will be included in the EU's quota system.

For the first two purposes the system boundaries – where in the life cycle you start and finish your calculations – vary.

For the last purpose, of national climate accounting, the calculations are done per sector and without a value chain perspective.

The study is very relevant for the ongoing efforts in establishing an EU certification framework for permanent carbon removal, carbon farming and carbon storage in products (CRCF).

• Read the full report here: Methodology for documenting negative emissions and Carbon Dioxide Removals (CDRs) applied for different intended purposes – Based on a Waste to Energy (WtE) BECCS case