How are greenhouse gas emissions calculated?

In France and the UK, independent organizations this week criticized their respective governments’ climate action, pointing to shortcomings in public policies to meet targets set to reduce greenhouse gas emissions.

The national greenhouse gas inventories make it possible to ensure compliance with the commitments of the signatories within the framework of the Paris Agreement. But how are these emissions measured?

What is a greenhouse gas?

Greenhouse gases are gases that absorb infrared radiation (part of the sun’s rays) emitted by the earth’s surface. They thus contribute to the greenhouse effect, which allows a reasonable temperature on the earth’s surface.

The so-called anthropogenic emissions caused by human activities are taken into account for the national inventories. If there is a large increase in the atmosphere, they are responsible for global warming.
Estimates instead of measurements

National inventories of greenhouse gas emissions are constructed from estimates using a simple mathematical formula. Emissions are calculated by multiplying the amount of activity by an “emission factor” related to the substance under consideration.
For countries that are unable to determine national values ​​for their emission factors, the UN climate experts (IPCC) offer standard data.

The emission factor makes it possible to convert the consumption of the various energies into the amount of greenhouse gases.

Countries follow the IPCC guidelines for reporting. It develops recommendations for data collection methods, sectors to monitor, and the “global warming potential” of each gas.

This is an index that “allows, in particular, to compare the relative impacts of greenhouse gases on climate change” by converting direct emissions into “CO2 equivalents” (eqCO2), explains Citepa, an organization running the French inventory. It is the “Global Warming Potential (GWP) that represents the impact of a greenhouse gas on the climate”.
Affected countries

Not all countries have equal responsibilities under the United Nations Climate Change Convention (UNFCCC). The so-called Annex 1 countries, which include all members of the OECD but also Russia, have committed to reducing their emissions and to presenting an inventory report two years after the year under review.
For the rest of the world, which “today emits 70% of the Earth’s greenhouse gas emissions, there is no obligation other than to try to periodically make national communications that are less precise, that are not in a harmonized format at all “, explains Philippe Ciais, research director at the Laboratory of Climate and Environmental Sciences (LSCE) and author of the IPCC.

China, the largest emitter of greenhouse gases, and the Gulf States belong to this category.

Sectors and gases to be monitored

The most important sectors are screened:

– Energy, including all fuel combustion activities in industry, transport and construction.
– industrial processes, for example cement or glass production, chemical, electronics, metal industries, but also the use of products to replace ozone-depleting substances
– Agriculture, forestry and other land uses
– waste treatment

The main greenhouse gases identified by the IPCC are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), used in particular in spray propellants, perfluorocarbons (PFCs) in air conditioning, sulfur hexafluoride (SF6), which is used as thermal insulation is used, and nitrogen trifluoride (NF3), which is used in microelectronics.

National inventories reported to the UNFCCC also include emissions of four indirect greenhouse gases: carbon monoxide (CO), non-methane volatile organic compounds (NMVOC), nitrogen oxides (NOx), and sulfur (SOx).

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