Better model to calculate exactly how much CO2 a country emits on balance

Policymakers and scientists use two different methods to calculate how much CO₂ a country emits, making it sometimes unclear how much that country must reduce its emissions to prevent dangerous climate change.

That is why a team of international scientists created a model to compare the figures of these different methods. The researchers describe their model in the trade magazine Nature. This allowed them to calculate the difference in how quickly countries will reduce their CO in the future₂emissions have been reduced enough under different scenarios.

To prevent dangerous climate change, many countries pledged their CO₂reduce emissions to zero, net zero. This is necessary to achieve the 2015 Paris targets. There, countries agreed to keep global warming well below 2 degrees Celsius compared to pre-industrial levels, preferably below 1.5°C. With every fraction of a degree of warming, the risk of heat waves, forest fires and floods increases.

Land use

Net zero does not mean that countries have no CO at all₂ are allowed to emit more; there is room for offsetting emissions by, for example, planting trees that reduce the CO emitted₂ record again. As long as the total emissions below the line are zero. To achieve this, countries calculate how much CO every year₂ they emit and how much they reabsorb. A kind of cash book.

That scientists and policymakers use different methods to reduce CO₂It has been known for some time to track emissions from countries. It is not that one method is correct and the other is not; they are different because scientists work with models, while policy makers take stock in the real world. The IPCC, the United Nations scientific climate agency, has been trying to develop a universal measuring method for some time.

The difference is mainly in the calculations of the CO₂-emissions related to changes in land use, for example cutting down or planting forests or draining peat soil. “The IPCC, the scientists, only look at human-induced change on land with their models,” says climate scientist Ronald Hutjes of Wageningen University. He is not involved in the study. “A forest takes in more CO₂ because people planted trees there? Then, according to the IPCC, it may be included in the accounting. If new forests grow in Siberia due to global warming, a country may not deduct this from their emissions. That is not an effort by a country to reduce CO₂emissions to reduce.”

On the policy side, the UN climate agency UNFCCC, it is difficult to make that distinction. Policy makers want to know how much CO₂ it is being recorded. This is calculated, for example, using satellites that see the size of a forest in a managed area, or they count trees. It is not clear which part of the growth is due to human effort and which part is due to, for example, increasing CO₂concentrations. Trees have CO₂ needed to grow.

Five years faster

The researchers compared when the countries will be in the coming decades net zero would achieve according to the UNFCC measurement method and according to the IPCC models. “For this we used a simple, existing climate model,” says the lead author of the study, Matthew Gidden of the Austrian institute IIASA. “We did thousands runs in which we looked at how the climate changed and how forests, for example, responded to that.”

What turned out? “We saw that the world was changing up to five years faster net zero can be achieved according to the UNFCC method compared to the IPCC scientific method.” So it may be that countries are more likely to say that they net zero achieved, while this is not the case according to the stricter IPCC.

Hutjes: “This once again shows how important it is to take differences in measurement methods into account. The way you use CO₂ uptake or emissions mainly matters for forested countries such as Canada. In the Netherlands, changes in forests do not outweigh the amount of CO₂ emitted by the combustion of fossil fuels.