How are greenhouse gas emissions calculated?

How are greenhouse gas emissions calculated?

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In France and the United Kingdom, independent bodies criticized their respective governments' climate action this week, pointing to shortcomings in public policies to meet targets for reducing greenhouse gas emissions. greenhouse effect fixed. 

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

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 surface of the Earth.

For the national inventories, the so-called anthropogenic emissions resulting from human activities are taken into consideration. Largely increasing in the atmosphere, they are responsible for global warming.

National inventories of greenhouse gas emissions are made from estimates, according to a simple mathematical formula. Emissions are calculated by multiplying the amount of activity by an “emission factor” relating to the substance under consideration.

For countries that do not have the possibility to determine national values ​​for their emission factors, the UN climate experts (IPCC) offer default data.

The emission factor allows consumption levels of different energies to be converted into quantities of greenhouse gases.

Countries follow 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 which “allows in particular to compare the relative impact of greenhouse gases on climate change”, by converting direct emissions into “equivalent CO2” (eqCO2), explains Citepa, an organization which carries out the French inventory. It is the “global warming potential (GWP) representing the impact of a greenhouse gas on the climate”.

Not all countries have the same responsibilities under the United Nations Convention on Climate Change (UNFCCC). The so-called Annex 1 countries, which includes all OECD members but also Russia, have made commitments to reduce their emissions and provide an inventory report available two years after the year observed.

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For the rest of the world, which “today emits 70% of the planet's greenhouse gas emissions, there is no other obligation than to try to make national communications at regular intervals, which are less precise, which are not at all in a harmonized format”, explains Philippe Ciais, research director at the Laboratory of Climate and Environmental Sciences (LSCE) and author of the IPCC.

China, the biggest emitter of greenhouse gases, and the Gulf countries are in this category.

The major sectors are screened:

– energy, with all fuel burning activities of industries, transport, construction.

– industrial processes, for example the production of cement or glass, the chemical, electronics, metal industries, but also the uses of products as substitutes for 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) found in air conditioners, sulfur hexafluoride (SF6) used as thermal insulation and nitrogen trifluoride (NF3) 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 (NMVOCs), nitrogen oxides (NOx) and oxides es of sulfur (SOx).