The Greenhouse Gas Inventories - calculating country-level emissions

By Charlotta Henry

In the labyrinth of climate data, where every number tells a story, the national greenhouse gas inventories serve as an important information source for the Global Stocktake. The inventories typically rely on estimations, but ground-based measurements can contribute to the verification of these.

Estimates, data and reports form the scientific core of the Global Stocktake. At the centre of this operation are the national greenhouse gas inventories. Dirk Günther, the Head of the Emission Situation Section at the German Environment Agency, explains how the inventories are produced:

“We calculate emissions based on national official statistical data. The calculation is pretty simple. We take the activity data, for example the amount of produced steel, animals in the agricultural sector and the amount of coal burned in power plants and multiply this with a specific emission factor of a gas or pollutant.” 

The greenhouse gas inventories are the monitoring and reporting building blocks of the UNFCCC MRV system. The verification consists of an international technical review of the inventories by a team of international experts that produces a report for each country with recommendations or encouragements. 

“The inventory needs to be transparent, and the calculation has to be plausible. One also needs to be able to follow how the calculation has been made. The calculation needs to be accurate and comparable,” Günther explains.

Photo: German Environment Agency
Frederik Pischke and Dirk Günther at the German Environmental Agency are both involved in the Global Stocktake process. According to Günther, combining observational data, estimates and calculations gives the most reliable results. Photo: German Environment Agency.

Statistics versus measurements

The greenhouse gas inventories not only show what the countries are releasing into the atmosphere in terms of emissions but also calculate carbon sinks and carbon removal from land use change and forestry. In Germany, this is done every decade. In between, a forest carbon stocktake is also done every five years and carbon removals are calculated on an annual basis using official forest and timber statistics. 

“Every 10 years, we do an inventory of our forests with actual measurements, where people go to the woods, measuring the trees on certain reference points. Then, there is a model for calculating the increase or decrease of the forest sinks based on the statistics, the harvesting and weather extremes,” says Günther.

Actual measurements and observational ground-based data can also add to the estimations and calculations of the greenhouse gas inventories. However, for most emission categories, the calculation is more accurate than the observation:

“Ground-based observations cannot distinguish whether the methane emission source is the cattle farm or the waste disposal site. In the iron and steel industry, we have to distinguish between five different sources from steel plants. An observation could never distinguish these five sources because it is just one attribute.”

If the inventory reports higher emissions of methane for example, the observational data cannot show why there is an increase. This requires other statistical data and/or models. Combining both observational data, estimates and calculations is the best method, according to Günther.

“Measurement data is already really good for the verification of the inventories. If you're talking about the verification of national totals, then you can compare," says Günther. 

"We observed this amount of methane and the calculation from the inventories gives another number, then you can try to explore. What is the reason for the differing numbers?”