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Seasonal Carbon Swing: Cleanest and Dirtiest Months by Country

Georgia has the biggest seasonal carbon swing of the 74 countries scored: its grid is cleanest in May (24 gCO2/kWh) and dirtiest in February (337 gCO2/kWh), a gap of 313 gCO2/kWh, on average over 2021 to 2025. The median country swings 77 gCO2/kWh, 24% of its own average. Relative to its average, Georgia swings most among grids averaging at least 100 gCO2/kWh: 181%. Outside the tropics, 26 of 65 countries are dirtiest in their local winter and 11 in their local summer.

Key Facts, Ember monthly data, complete years 2021 to 2025

  • 74 countries were scored from Ember monthly data, using complete calendar years 2021 to 2025 (at least 3 of the 5 years for each country, the number is in the table).
  • Georgia: 24 gCO2/kWh in May to 337 gCO2/kWh in February, a swing of 313 gCO2/kWh (181% of its average) over 2021 to 2025.
  • The five biggest swings in gCO2/kWh: Georgia 313, Sri Lanka 302, Bosnia and Herzegovina 219, Bulgaria 218 and Pakistan 207.
  • The five biggest swings relative to the average, for grids averaging at least 100 gCO2/kWh: Georgia 181%, Finland 87%, Slovenia 83%, New Zealand 80% and Croatia 73%.
  • Steadiest across the year (swing as a share of the average) among grids averaging at least 100 gCO2/kWh: Kuwait 0.0%, Qatar 0.0%, Oman 0.0%, Singapore 0.7% and Tunisia 1.4%.
  • The median swing is 77 gCO2/kWh (24% of the average); January is the dirtiest month for 14 countries and May the cleanest for 19.
  • Of 65 countries more than 10 degrees from the equator, 26 have their dirtiest month in local winter, 11 in local summer and 28 in spring or autumn.
  • 141 of the 215 countries in the export were not scored: 127 have no monthly statistics, 13 of the 88 that do generate under 10 TWh, and 1 has fewer than 3 complete years in 2021 to 2025.

Which Countries Swing Most

Complete years 2021 to 2025

Largest swing, in gCO2/kWh

Countries with the largest gap between their dirtiest and cleanest month, in grams of CO2 per kilowatt hour
CountryCleanestDirtiestSwing
1. ๐Ÿ‡ฌ๐Ÿ‡ช Georgia May 24 Feb 337 313
2. ๐Ÿ‡ฑ๐Ÿ‡ฐ Sri Lanka Nov 265 Mar 567 302
3. ๐Ÿ‡ง๐Ÿ‡ฆ Bosnia and Herzegovina Mar 592 Sep 811 219
4. ๐Ÿ‡ง๐Ÿ‡ฌ Bulgaria Jun 282 Nov 500 218
5. ๐Ÿ‡ต๐Ÿ‡ฐ Pakistan Nov 285 Jan 493 207
6. ๐Ÿ‡ธ๐Ÿ‡ฎ Slovenia May 125 Oct 326 201
7. ๐Ÿ‡ท๐Ÿ‡ธ Serbia May 605 Aug 803 198
8. ๐Ÿ‡ป๐Ÿ‡ณ Vietnam Aug 361 Apr 558 197
9. ๐Ÿ‡ต๐Ÿ‡ช Peru Apr 188 Sep 356 168
10. ๐Ÿ‡จ๐Ÿ‡ฑ Chile Nov 235 Apr 392 157

Largest swing, share of the average

Countries with the largest gap between their dirtiest and cleanest month as a share of their average, for grids averaging at least 100 grams per kilowatt hour
CountryAverageSwingShare
1. ๐Ÿ‡ฌ๐Ÿ‡ช Georgia 174 313 181%
2. ๐Ÿ‡ซ๐Ÿ‡ฎ Finland 108 93 87%
3. ๐Ÿ‡ธ๐Ÿ‡ฎ Slovenia 242 201 83%
4. ๐Ÿ‡ณ๐Ÿ‡ฟ New Zealand 114 92 80%
5. ๐Ÿ‡ญ๐Ÿ‡ท Croatia 208 153 73%
6. ๐Ÿ‡ฑ๐Ÿ‡ฐ Sri Lanka 412 302 73%
7. ๐Ÿ‡ต๐Ÿ‡ช Peru 277 168 61%
8. ๐Ÿ‡ต๐Ÿ‡ฐ Pakistan 373 207 56%
9. ๐Ÿ‡ฐ๐Ÿ‡ฌ Kyrgyzstan 144 78 54%
10. ๐Ÿ‡ง๐Ÿ‡ฌ Bulgaria 409 218 53%

Figures are gCO2/kWh. The absolute ranking favours big, fossil heavy grids; the share ranking is limited to the 64 grids averaging at least 100 gCO2/kWh, because a grid at 20 gCO2/kWh can swing 100% of its average with a change that is tiny in absolute terms. Median across all 74: 77 gCO2/kWh, 24% of the average.

Average carbon intensity by calendar month, 5 countries with the largest seasonal swing, 2021 to 2025 Average gCO2/kWh for each calendar month, 2021 to 2025, for Georgia, Sri Lanka, Bosnia and Herzegovina, Bulgaria and Pakistan. Georgia runs from 24 gCO2/kWh in May to 337 gCO2/kWh in February, Sri Lanka runs from 265 gCO2/kWh in November to 567 gCO2/kWh in March, Bosnia and Herzegovina runs from 592 gCO2/kWh in March to 811 gCO2/kWh in September, Bulgaria runs from 282 gCO2/kWh in June to 500 gCO2/kWh in November and Pakistan runs from 285 gCO2/kWh in November to 493 gCO2/kWh in January. 0 250 500 750 1,000 JanFebMarAprMayJunJulAugSepOctNovDec
Average gCO2/kWh for each calendar month, 2021 to 2025, for Georgia, Sri Lanka, Bosnia and Herzegovina, Bulgaria and Pakistan. Georgia runs from 24 gCO2/kWh in May to 337 gCO2/kWh in February, Sri Lanka runs from 265 gCO2/kWh in November to 567 gCO2/kWh in March, Bosnia and Herzegovina runs from 592 gCO2/kWh in March to 811 gCO2/kWh in September, Bulgaria runs from 282 gCO2/kWh in June to 500 gCO2/kWh in November and Pakistan runs from 285 gCO2/kWh in November to 493 gCO2/kWh in January.
Ember monthly statistics, complete years 2021 to 2025, gCO2/kWh
Average carbon intensity by calendar month, 5 countries with the largest seasonal swing, 2021 to 2025
MonthGeorgiaSri LankaBosnia and HerzegovinaBulgariaPakistan
January323485641471493
February337552619453381
March212567592395400
April57516640370406
May24413629390383
June25356693282385
July41380751360355
August131387792354334
September183384811385331
October179333743480360
November255265693500285
December314308626474362

Which Months Are Cleanest and Dirtiest

74 countries
Number of countries for which each calendar month is the dirtiest or the cleanest on average
MonthCountries where it is dirtiestCountries where it is cleanest
January144
February75
March67
April25
May219
June57
July25
August67
September61
October76
November85
December93

Seasons depend on the hemisphere, so for the 65 countries more than 10 degrees from the equator the dirtiest month falls in local winter for 26, local summer for 11 and spring or autumn for 28. Winter is December to February in the north and June to August in the south; latitude comes from the world outlines and is good to a few degrees.

Every Country

74 countries, biggest swing first
Cleanest and dirtiest calendar month on average with their carbon intensity, the swing in grams of CO2 per kilowatt hour and as a share of the average, the average and the number of years used, for each scored country. Column headings sort the table.
CountryCleanest monthCleanest gCO2/kWhDirtiest monthDirtiest gCO2/kWhSwingSwing, share of averageAverageYears used
๐Ÿ‡ฌ๐Ÿ‡ช GeorgiaMay24February337313181%1745 (all)
๐Ÿ‡ฑ๐Ÿ‡ฐ Sri LankaNovember265March56730273%4124 (2021 to 2025)
๐Ÿ‡ง๐Ÿ‡ฆ Bosnia and HerzegovinaMarch592September81121932%6865 (all)
๐Ÿ‡ง๐Ÿ‡ฌ BulgariaJune282November50021853%4095 (all)
๐Ÿ‡ต๐Ÿ‡ฐ PakistanNovember285January49320756%3735 (all)
๐Ÿ‡ธ๐Ÿ‡ฎ SloveniaMay125October32620183%2425 (all)
๐Ÿ‡ท๐Ÿ‡ธ SerbiaMay605August80319828%7135 (all)
๐Ÿ‡ป๐Ÿ‡ณ VietnamAugust361April55819743%4555 (all)
๐Ÿ‡ต๐Ÿ‡ช PeruApril188September35616861%2775 (all)
๐Ÿ‡จ๐Ÿ‡ฑ ChileNovember235April39215750%3155 (all)
๐Ÿ‡น๐Ÿ‡ท TurkeyApril386November54215632%4855 (all)
๐Ÿ‡ญ๐Ÿ‡ท CroatiaMay129October28215373%2085 (all)
๐Ÿ‡จ๐Ÿ‡ฟ CzechiaJune366January51014432%4485 (all)
๐Ÿ‡ฎ๐Ÿ‡ช IrelandFebruary254July38613240%3315 (all)
๐Ÿ‡น๐Ÿ‡ฏ TajikistanJuly25March155130142%925 (all)
๐Ÿ‡ฏ๐Ÿ‡ต JapanMay403January52212025%4725 (all)
๐Ÿ‡ง๐Ÿ‡ด BoliviaMarch467November58011322%5225 (all)
๐Ÿ‡ณ๐Ÿ‡ฑ NetherlandsMay234January34511138%2925 (all)
๐Ÿ‡ฉ๐Ÿ‡ช GermanyMay327November43711028%3875 (all)
๐Ÿ‡บ๐Ÿ‡พ UruguayOctober58January167109116%945 (all)
๐Ÿ‡ฎ๐Ÿ‡น ItalyMay266December37310733%3305 (all)
๐Ÿ‡ฆ๐Ÿ‡น AustriaJune47December154107107%1005 (all)
๐Ÿ‡ฎ๐Ÿ‡ณ IndiaAugust619January72510716%6805 (all)
๐Ÿ‡จ๐Ÿ‡ณ ChinaMay577January67910217%6145 (all)
๐Ÿ‡ฆ๐Ÿ‡บ AustraliaDecember535June6319616%5855 (all)
๐Ÿ‡ซ๐Ÿ‡ฎ FinlandJuly61January1549387%1085 (all)
๐Ÿ‡ฉ๐Ÿ‡ฐ DenmarkOctober159March2539346%2055 (all)
๐Ÿ‡ณ๐Ÿ‡ฟ New ZealandNovember59March1519280%1145 (all)
๐Ÿ‡ฆ๐Ÿ‡ท ArgentinaOctober291January3808926%3475 (all)
๐Ÿ‡ช๐Ÿ‡จ EcuadorJune147December2368947%1895 (all)
๐Ÿ‡ท๐Ÿ‡ด RomaniaApril231November3198831%2855 (all)
๐Ÿ‡ณ๐Ÿ‡ฌ NigeriaOctober476June5628617%5185 (all)
๐Ÿ‡บ๐Ÿ‡ธ United StatesApril353July4378421%3975 (all)
๐Ÿ‡ท๐Ÿ‡บ RussiaJune387February4708319%4305 (all)
๐Ÿ‡ญ๐Ÿ‡บ HungaryJune184December2678338%2205 (all)
๐Ÿ‡จ๐Ÿ‡ด ColombiaMay135February2147946%1705 (all)
๐Ÿ‡ฐ๐Ÿ‡ฌ KyrgyzstanAugust103October1817854%1445 (all)
๐Ÿ‡ฌ๐Ÿ‡ท GreeceMay318December3947621%3585 (all)
๐Ÿ‡ต๐Ÿ‡ฑ PolandMay691November7677610%7295 (all)
๐Ÿ‡ต๐Ÿ‡น PortugalMarch131September2057444%1695 (all)
๐Ÿ‡ฒ๐Ÿ‡ฆ MoroccoJuly613December6847111%6445 (all)
๐Ÿ‡ฐ๐Ÿ‡ท South KoreaMay387August4546716%4205 (all)
๐Ÿ‡ฟ๐Ÿ‡ฆ South AfricaDecember676June742669%7195 (all)
๐Ÿ‡ฆ๐Ÿ‡ฟ AzerbaijanMay651February715649%6965 (all)
๐Ÿ‡ต๐Ÿ‡ญ PhilippinesJanuary606May6706410%6395 (all)
๐Ÿ‡ฐ๐Ÿ‡ฟ KazakhstanMay787February849628%8185 (all)
๐Ÿ‡จ๐Ÿ‡ท Costa RicaNovember25May8056115%485 (all)
๐Ÿ‡ฎ๐Ÿ‡ท IranMarch630October683528%6614 (2021 to 2024)
๐Ÿ‡ช๐Ÿ‡ธ SpainMarch134September1855132%1635 (all)
๐Ÿ‡น๐Ÿ‡ผ TaiwanFebruary611August662518%6405 (all)
๐Ÿ‡ธ๐Ÿ‡ฐ SlovakiaAugust99January1484939%1245 (all)
๐Ÿ‡ง๐Ÿ‡พ BelarusMay379September4274812%4085 (all)
๐Ÿ‡ง๐Ÿ‡ท BrazilMarch89October1294137%1115 (all)
๐Ÿ‡ฌ๐Ÿ‡ง United KingdomOctober222January2624017%2385 (all)
๐Ÿ‡จ๐Ÿ‡ฆ CanadaApril156August1953923%1745 (all)
๐Ÿ‡ฉ๐Ÿ‡ด Dominican RepublicJuly579October617396%5953 (2023 to 2025)
๐Ÿ‡น๐Ÿ‡ญ ThailandDecember537October572366%5565 (all)
๐Ÿ‡ฐ๐Ÿ‡ช KenyaJune68February1033541%855 (all)
๐Ÿ‡ช๐Ÿ‡ฌ EgyptMay553January585326%5685 (all)
๐Ÿ‡ง๐Ÿ‡ช BelgiumMay147November1762918%1625 (all)
๐Ÿ‡ซ๐Ÿ‡ท FranceMay32January592760%455 (all)
๐Ÿ‡ฒ๐Ÿ‡พ MalaysiaJanuary620June646264%6365 (all)
๐Ÿ‡ฒ๐Ÿ‡ฝ MexicoSeptember480June502225%4915 (all)
๐Ÿ‡ต๐Ÿ‡ท Puerto RicoAugust709March730213%7215 (all)
๐Ÿ‡ง๐Ÿ‡ฉ BangladeshJuly735December747122%7395 (all)
๐Ÿ‡จ๐Ÿ‡ญ SwitzerlandAugust50February601018%565 (all)
๐Ÿ‡น๐Ÿ‡ณ TunisiaJanuary568August57681%5715 (all)
๐Ÿ‡ธ๐Ÿ‡ช SwedenAugust22December28623%255 (all)
๐Ÿ‡ธ๐Ÿ‡ฌ SingaporeOctober473January47741%4755 (all)
๐Ÿ‡ณ๐Ÿ‡ด NorwayFebruary27August2929%285 (all)
๐Ÿ‡ฎ๐Ÿ‡ธ IcelandMarch17September1715%175 (all)
๐Ÿ‡ด๐Ÿ‡ฒ OmanFebruary601December60100%6015 (all)
๐Ÿ‡ถ๐Ÿ‡ฆ QatarJanuary604November60400%6044 (2021 to 2024)
๐Ÿ‡ฐ๐Ÿ‡ผ KuwaitFebruary650March65000%6504 (2021 to 2024)

Column headings sort the table. Every figure is an average of that calendar month over the years used, in gCO2/kWh; months sort in calendar order. 5 countries have fewer than all 5 years (Sri Lanka, Iran, Dominican Republic, Qatar, Kuwait), so their averages cover fewer years and are more sensitive to one unusual year.

How This Is Measured, and Caveats

  • Data: Ember monthly carbon intensity, gCO2/kWh, from the 88 of 215 countries in the export that have monthly statistics. 127 countries have annual figures only and cannot be scored.
  • Years: only complete calendar years are used, meaning all twelve months have a positive carbon intensity. Part years, such as the newest months of the current year, are never used, so no season counts twice. The common window is the 5 calendar years ending at the newest year that at least 80% of countries with monthly data have complete: 2021 to 2025. A country needs at least 3 complete years inside the window; 1 did not.
  • Each calendar month's figure is the plain average of that month's carbon intensity across the years used. It is not weighted by the amount generated. The cleanest and dirtiest months are the lowest and highest of the twelve averages, an exact tie going to the earlier month, and the swing is the dirtiest minus the cleanest.
  • Who is scored: countries generating at least 10 TWh in their latest annual year (13 smaller countries with monthly data are left out), because one plant can set the monthly average of a small grid.
  • Averages over at most 5 years are sensitive to weather. One very dry year can move a hydro country's dirtiest month, and where two months are close the order could change with other years; small gaps between months should be read as ties.
  • A small swing does not mean a clean grid. The steadiest grids averaging at least 100 gCO2/kWh (Kuwait, Qatar, Oman, Singapore, Tunisia) swing 0.0% to 1.4% of their average, at 475 to 650 gCO2/kWh, which fits grids that rely on one fossil fuel all year.
  • Carbon intensity here is Ember's figure for electricity generated in the country, not for electricity used: trade is not included. The page shows the size and timing of the pattern, not its cause.

Seasonal Carbon Swing FAQ

Which countries have the biggest seasonal swing in carbon intensity?

Georgia (313 gCO2/kWh), Sri Lanka (302 gCO2/kWh), Bosnia and Herzegovina (219 gCO2/kWh), Bulgaria (218 gCO2/kWh) and Pakistan (207 gCO2/kWh) have the largest gap between their dirtiest and cleanest calendar month, averaged over complete years 2021 to 2025, among 74 countries generating at least 10 TWh.

Why does carbon intensity change through the year?

The mix changes: hydro and wind output follow rain, snow melt and wind seasons, solar follows the sun, and heating or cooling demand pulls in more gas or coal when the cheaper sources are not enough. This page measures the size and timing of the pattern, not its cause, which differs country by country.

Which years are used?

Only complete calendar years, 2021 to 2025, in which all twelve months have a carbon intensity. Part years, including the newest months of the current year, are left out so no season counts more than another. Each calendar month is the plain average of that month across the years used.

Is the cleanest month the same every year?

Not always. The months here are averages over at most 5 years, and a wet or windy year can move a country's cleanest month. For grids where two months are close, the order could change with different years, so treat small gaps between months as ties.

Why are only some countries included?

Ember publishes monthly statistics for 88 of 215 countries. 13 of those generate under 10 TWh a year and 1 lack 3 complete years in the window. The rest have annual figures only, on their own country pages.

Source: Ember (ember-energy.org), licensed under CC BY 4.0. Data as of complete years 2021 to 2025. Monthly statistics from Ember; complete calendar years only.

Cite this page
APA 7

World Power Monitor. (2025). Seasonal Carbon Swing: Cleanest and Dirtiest Months by Country. https://worldpowermonitor.com/carbon-seasons/

Plain text

World Power Monitor. Seasonal Carbon Swing: Cleanest and Dirtiest Months by Country. Data as of 2025. Data from Ember. https://worldpowermonitor.com/carbon-seasons/

BibTeX 
@misc{wpm_carbon_seasons_2025,
  title = {{Seasonal Carbon Swing: Cleanest and Dirtiest Months by Country}},
  author = {{World Power Monitor}},
  year = {2025},
  note = {Data as of 2025. Data from Ember.},
  url = {https://worldpowermonitor.com/carbon-seasons/}
}

Permalink: https://worldpowermonitor.com/carbon-seasons/

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