What CO2 do we actually include in the MPG?

Sometimes it seems like we're comparing apples and oranges...

When trees are felled for industrial purposes other than combustion, the CO2 stored in the wood is retained during growth. This CO2 storage remains in effect as long as the wood is used as a product. However, many standardized methods for calculating the CO2 impact of products do not allow this storage to be included, or to be attributed to a wood product. This also applies to the widely used National Environmental Database, MKI, and the related MPG calculations for the (Dutch) built environment. In many other European countries, the CO2 storage of wood and other biobased materials (flax, hemp, cellulose) is included. In fact, the European standard (EN 15804) assigns negative emissions (CO2 absorption) to the use of biobased products in the A1 (production) phase, while end-of-life emissions (e.g., during combustion) are reported in module D.

How does CO2 actually get into wood and biobased materials?

CO2 is stored in everything around us and forms a natural carbon cycle. We can roughly distinguish between (long-cycle) geological CO2 storage, atmospheric CO2 storage, ocean CO2 storage, mineral CO2 storage, and (short-cycle) carbon storage in plants and soil. Geological CO2 storage occurs in underground reservoirs, for example, where fossil fuels are extracted. Oil, gas, and coal, as raw materials, were also originally biobased products. The major difference is that the sources from which we extract these fuels are billions of years old. Therefore, it takes billions of years for them to regenerate. For centuries, the carbon stock was in balance, but the combustion of long-cycle sources has created an imbalance. An additional problem with geological storage is that the potential storage locations are usually far removed from the CO2 emission sources.

Scientific debate

There has been a long debate among academics about whether biogenic CO2 storage should be included in life cycle assessments (LCAs) in the IPCC's climate policy. A majority of scientists agreed that temporary CO2 sequestration (i.e., less than 100 years) should not be included. For example, if a wooden product is used temporarily, the CO2 will be released back into the atmosphere after the product's use. The sequestration is therefore temporary. The debate has now moved on. The European standard EN 15804 assigns negative emissions to biobased products and does include the temporarily stored CO2. However, the Netherlands has not (yet) incorporated this standard into its Determination Method. In many other European countries, however, the CO2 storage of wood and other biobased materials (flax, hemp, cellulose) is included.

When a wood product is burned at the end of its lifespan, heat and electricity are released. This heat and electricity, if burned in a biomass plant, can replace the required energy, which often comes from fossil fuels (oil, gas, and/or coal). This energy saving can be included as a CO2 reduction in many LCA calculation methods. However, in the Netherlands—unlike all other countries—the latest version of the NMD assumes that the national energy mix is not conserved at the end of its lifespan, resulting in low savings. Furthermore, there are many other options besides burning a product at the end of its lifespan.

Biobased raw material flows are ideally suited for long-term use and beneficial applications of the raw materials used. When biobased products are decommissioned, original elements, such as lignin, can often be recovered. This can then be used to make new products. And if that is no longer possible, a product can be composted, which not only reintroduces the CO2 into the cycle but also returns the other minerals used to their original position in the chain. This principle is also known as cascading. Cascading biobased products offers many environmental advantages over products made from abiotic raw materials, thanks to the possibilities described above.

From forests to CO2 storage in the built environment
The calculation method for CO2 savings from burning biomass is only truly accurate if the total forest area, and thus the CO2 absorption of the forested area, remains the same. If we cut down wood, produce products that we burn, and don't replant trees, we disrupt the CO2 balance. This is because we release previously captured CO2 into the atmosphere. But what if we were to use more wood, for example, in the built environment? Suppose we use wood instead of concrete elements in new buildings, then more forest is needed. If planting more forests leads to an increase in the area, then there will be a net increase in CO2 storage due to the use of wood.

The figure below shows that wood production contributes to an increase in CO2 storage by forests in the early years. After 45 years, the first trees are felled and used in wood products that replace concrete walls and floors in residential construction. CO2 is thus captured in a building. Furthermore, a significant portion of CO2 emissions is avoided because concrete, with its high associated CO2 emissions, is replaced as a product. Over the following years, CO2 storage per hectare of forest remains the same. The avoided emissions by replacing concrete increase each time the forest is felled and the wood is used in construction. This figure assumes that the products do not last longer than 100 years. If the products were to last longer than 100 years, there would be a net absorption and thus a reduction of atmospheric CO2 (the figure below is somewhat exaggerated in terms of figures).

CO2 storage: should it be included or not?

Temporary CO2 storage doesn't have to be limited to wood. Concrete, for example, can also provide CO2 storage if captured CO2 emissions are reused through Carbon Capture & Utilization in long-lasting concrete building products. Canadian startup Injects concrete with CO2, which causes the concrete mixture to harden and become stronger, thus achieving several advantages such as a longer lifespan, a wider range of applications, and temporary CO2 storage (although less than the CO2 naturally stored in wood). If this CO2 comes from biomass plants that use residual wood and other waste streams, then in theory the same temporary CO2 sequestration occurs as with wood, but this method does require energy. This CO2 storage, too, cannot be calculated and attributed to a product using current calculation methods. A concrete product without injected CO2 will receive a lower environmental impact score under these calculation methods than concrete products that do contain CO2, because only energy consumption and the associated CO2 emissions are included in the calculation.

Climate change is a problem that must be solved now. Therefore, we must look for solutions now and focus on reducing CO2 emissions during production (read: today). For many abiotic raw materials, recycling credits are awarded to products that are properly recycled at the end of their life cycle, which makes many products look more favorable when compared based on the final result. But how can we guarantee that the products we bring to market today will be properly recycled in 50 years? What we do know for sure is what is being produced now and the CO2 emissions it releases today. Addressing this in the short term can give us some breathing room in the long run.

What would it mean if CO2 storage in materials were included? 

1. If a wooden product or component, or other product with CO2 storage, whether or not cascaded, is used for more than 100 years, CO2 absorption takes place.
2. Products used for less than 100 years temporarily capture CO2, thus providing some breathing room in terms of climate change.
3. As sustainably managed timber production increases, and with it the total area of forested land, timber provides a net absorption of CO2 emissions.
4. Avoiding environmentally polluting, often abiotic, raw materials by replacing them with, for example, wood, cumulatively reduces total CO2 emissions over time.

 What does this mean for players in the construction industry?

• You can also reuse products with CO2 storage, for example by reusing old wooden support beams. Look here For our circular chain project in the province of North Holland, where we saved 7 km of wooden purlins from incineration. This ensures longer, temporary CO2 capture.
• Look at the Trias energetica and Trias Emergetica of buildings. The goal of the Trias Emergetica is ultimately to achieve the highest possible functional fulfillment using materials with the lowest possible embodied energy over the longest possible period.
• As a supplier, find out which materials you use generate the most CO2 emissions and absorb the most CO2. You can do this, for example, through our baseline measurement in which we provide insight into where you can reduce your responsible CO2 emissions by 80 percent in 5 years.