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Why it’s not so easy to calculate global greenhouse gas emissions

Julien Vincent
Head of Mitigation and Adaptation at Citepa
Étienne Mathias
Head of Agriculture, Forestry and Land use at Citepa
Key takeaways
  • According to the national greenhouse gas inventories, the largest emitters of GHGs are, in order, China, the US and the EU.
  • However, levels of accuracy may vary from one sector to another, as GHG emissions are not always calculated using the same set of parameters.
  • The choice of GHG emissions indicator significantly affects the results and even the ranking of emitting countries.
  • The carbon footprint, which takes into account the emissions linked to the consumption of citizens, including imports, is particularly relevant.
  • In 2019, half the population was responsible for 12% of global emissions compared to the richest who were responsible for almost 50%.

Who is respon­si­ble for world green­house gas (GHG) emis­sions? Which coun­tries are exem­plary, which cit­i­zens are major con­trib­u­tors? The answer is far from sim­ple. And for good rea­son: there is no direct mea­sure­ment of GHG emis­sions at a nation­al lev­el. The mea­sure­ment of GHG emis­sions from human activ­i­ties is based on indi­rect esti­mates. For exam­ple, fuel sales data can be cross-ref­er­enced with their emis­sion fac­tor (i.e. the amount of GHG emit­ted per unit of ener­gy) to esti­mate trans­port-relat­ed emis­sions. This can be done for each of the GHG emit­ting or cap­tur­ing sec­tors: ener­gy, indus­tri­al process­es, agri­cul­ture, land use and waste.

Gaps in the indicator 

Chi­na leads with 11.2 Gt CO2e emit­ted in 2014, fol­lowed by the Unit­ed States (5.7 Gt CO2e in 2019), the Euro­pean Union (3.3 Gt CO2e in 2019) and India (2.5 Gt CO2e in 2016). These fig­ures are those of the nation­al green­house gas inven­to­ries, reg­u­lat­ed by the Kyoto Pro­to­col since 2005. They account for sev­en GHGs (CO2, CH4, N2O, HFCs, PFCs, SF6 and NF3) using a method defined by the Inter­gov­ern­men­tal Pan­el on Cli­mate Change (IPCC). Each coun­try in Annex I of the Unit­ed Nations Frame­work Con­ven­tion on Cli­mate Change (i.e. 43 States, includ­ing the Euro­pean Union1) is required to sub­mit its nation­al GHG inven­to­ry each year. This oblig­a­tion will be extend­ed to all mem­ber coun­tries from 2024.

The lev­els used vary from one sec­tor to anoth­er, from one coun­try to another.

Is this cal­cu­la­tion method the right one to use? “This indi­ca­tor is intend­ed for polit­i­cal pur­pos­es and is very use­ful for defin­ing the tools for imple­ment­ing nation­al strate­gies to reduce GHG emis­sions,” says Eti­enne Math­ias, a land sec­tor expert at Citepa, the organ­i­sa­tion respon­si­ble for cal­cu­lat­ing the inven­to­ry in France. “How­ev­er, it has sev­er­al short­com­ings for an inter­na­tion­al com­par­i­son. The IPCC defines guide­lines with dif­fer­ent lev­els of pre­ci­sion,” explains Julien Vin­cent, head of inven­to­ry method­ol­o­gy at Citepa. 

Emis­sions can be cal­cu­lat­ed on the basis of default para­me­ters (lev­el 1), rep­re­sen­ta­tive of the nation­al lev­el (lev­el 2), or even refined at the scale of a GHG emis­sion site (lev­el 3). The lev­els used vary from one sec­tor to anoth­er, from one coun­try to anoth­er. While this has lit­tle influ­ence on the cal­cu­la­tion of ener­gy-relat­ed CO2 emis­sions, oth­er sec­tors can show great vari­abil­i­ty between states. “Fugi­tive emis­sions from oil and gas extrac­tion (e.g. methane leaks) have very high lev­els of uncer­tain­ty, even for devel­oped coun­tries,” says Julien Vin­cent. Eti­enne Math­ias adds: “Releas­es from agri­cul­ture and espe­cial­ly the land sec­tor present even greater uncer­tain­ties, which can be as high as sev­er­al mil­lion tonnes of GHGs, par­tic­u­lar­ly as many unde­vel­oped coun­tries have lit­tle activ­i­ty data and emis­sion fac­tors.” Anoth­er lim­i­ta­tion is that only 48 coun­tries have sub­mit­ted at least one inven­to­ry to date.

New indicator, new results

To fill these gaps, let us look at one of the projects pro­vid­ing har­monised GHG emis­sion maps across the globe: the Cli­mate­Watch indi­ca­tor2 from the World Resources Insti­tute. It com­piles sev­er­al inter­na­tion­al data­bas­es. While the rank­ing remains unchanged, this time it shows that the 10 high­est emit­ting coun­tries togeth­er emit more GHGs than the rest of the world. For 2019, Chi­na’s total is 12 Gt CO2e (up sharply since the ear­ly 2000s), com­pared with 19.7 Gt CO2e for the rest of the world.

Beware the indi­ca­tor used

The choice of indi­ca­tor can strong­ly influ­ence the rank­ing. For exam­ple, whether or not to include the land sec­tor in the cal­cu­la­tion (often indi­cat­ed under the abbre­vi­a­tion LULUCF). This sec­tor takes into account land use, land-use change and forests: car­bon sources and sinks are there­fore account­ed for. “If the objec­tive is to look at the evo­lu­tion of emis­sions, it is log­i­cal to exclude car­bon sinks,” says Math­ias. While Chi­na and the US remain at the top of the rank­ing, India and the EU are now neck and neck when the land sec­tor is exclud­ed from the bal­ance sheet. On the oth­er hand, Indone­sia has dropped from 8th to 5th place in the rank­ing when LULUCF is includ­ed, from 1 Gt CO2e to 1.96 Gt CO2e: this reflects the sig­nif­i­cant defor­esta­tion in the country.Another point to con­sid­er is the emis­sions tak­en into account. Some indi­ca­tors include all GHGs (expressed in CO2e), oth­ers only CO2. This reduces the weight of cer­tain sec­tors in the bal­ance sheet, such as agri­cul­ture, which main­ly emits methane (CH4) and nitrous oxide (N2O).

So why do coun­tries like Chi­na have such high emis­sions? Part­ly because of their pop­u­la­tion size. Based on the Cli­mate­Watch indi­ca­tor for 2019, the high­est emit­ting cit­i­zens are those of the Solomon Islands (69.2 t CO2e/capita/year), Qatar (40.5 t CO2e/capita/year) and Bahrain (33.1 t CO2e/capita/year). Each Chi­nese cit­i­zen con­tributes 8.41 t CO2e each year. In India, the world’s fourth largest emit­ter of GHGs, emis­sions amount to only 2.4 tonnes of CO2e/inhab/yr.

Carbon footprint upsets the rankings

Anoth­er inter­est­ing aspect is car­bon foot­print­ing. Until now, the indi­ca­tors men­tioned only reflect the emis­sions of cit­i­zens with­in their own coun­try. Some coun­tries, such as Chi­na, are major exporters of goods and ser­vices. The car­bon foot­print, on the oth­er hand, takes into account the emis­sions linked to the con­sump­tion of cit­i­zens. It adds up the emis­sions of house­holds, domes­tic pro­duc­tion, and imports, minus the emis­sions asso­ci­at­ed with exports. For exam­ple, in the case of France, while ter­ri­to­r­i­al emis­sions amount to 5.4 t CO2e/inhabitant/year, the car­bon foot­print will rise to 8.9 t CO2e/inhabitant/year in 2021 accord­ing to the Ser­vice des don­nées et études sta­tis­tiques3. Indeed, more than half of France’s car­bon foot­print comes from import­ed goods and ser­vices and import­ed raw mate­ri­als or semi-fin­ished products.

There is no stan­dard­ized method for cal­cu­lat­ing car­bon foot­prints on a glob­al lev­el. Accord­ing to the Exiobase data­base4, a sig­nif­i­cant part of Chi­na’s emis­sions is due to the pro­duc­tion of goods and ser­vices for Europe or the US. While Chi­na accounts for 24.1% of glob­al GHG emis­sions, this fig­ure drops to 19.2% when con­sid­er­ing its car­bon foot­print, behind Europe (20.2% of the glob­al car­bon foot­print) and the US (19.8% of the glob­al car­bon footprint).

There is no stan­dard­ised method for cal­cu­lat­ing car­bon foot­prints on a glob­al level.

“You have to keep in mind what each of the indi­ca­tors illus­trates, they all have a dif­fer­ent pur­pose,” says Julien Vin­cent. “For exam­ple, per capi­ta emis­sions are aver­ages and do not rep­re­sent income lev­els and oth­er social inequal­i­ties.” In an arti­cle pub­lished in Nature Sus­tain­abil­i­ty in 20225, Lucas Chan­cel esti­mates that in 2019, half the pop­u­la­tion was respon­si­ble for 12% of glob­al GHG emis­sions. The rich­est 10% were respon­si­ble for 48% of glob­al GHG emis­sions in the same year.

Anaïs Marechal
1Web­site con­sult­ed on 30/11/2022: https://​unfc​cc​.int/​p​r​o​c​e​s​s​/​p​a​r​t​i​e​s​-​n​o​n​-​p​a​r​t​y​-​s​t​a​k​e​h​o​l​d​e​r​s​/​p​a​r​t​i​e​s​-​c​o​n​v​e​n​t​i​o​n​-​a​n​d​-​o​b​s​e​r​v​e​r​-​s​tates
2Data (as CAIT) avail­able at: https://​www​.cli​mate​watch​da​ta​.org/​g​h​g​-​e​m​i​s​s​i​o​n​s​?​s​o​u​r​c​e​=CAIT
3Accessed on 01/12/2022: https://www.statistiques.developpement-durable.gouv.fr/lempreinte-carbone-de-la-france-de-1995–2021
4Tukker, A., Bulavskaya, T., Giljum, S., de Kon­ing, A., Lut­ter, S., Simas, M., Stadler, K., Wood, R. 2014. The Glob­al Resource Foot­print of Nations. Car­bon, water, land and mate­ri­als embod­ied in trade and final con­sump­tion cal­cu­lat­ed with EXIOBASE 2.1. Leiden/Delft/Vienna/Trondheim.
5Chan­cel, L. Glob­al car­bon inequal­i­ty over 1990–2019. Nat Sus­tain 5, 931–938 (2022). https://doi.org/10.1038/s41893-022–00955‑z

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