Reykjavík Has a Warmer January Than Seoul: Why Latitude Doesn't Decide Winter

Reykjavík sits at 64.1°N, about 300km short of the Arctic Circle and 26.6 degrees of latitude north of Seoul. Its January mean is -1.5°C. Seoul's is -1.9°C. The capital of the country with ice in its name runs warmer.

It is not a fluke pairing. Of the 53 capitals in this dataset, 24 sit north of Seoul, and 22 of them are warmer in January. Only Ottawa and Pyongyang are colder. Turn it around and it gets starker: of the 28 capitals south of Seoul, not one is colder in January.

Washington D.C. belongs in this story too, and not as a warm outlier. At 38.9°N it is barely north of Seoul, and it averages -1.5°C in January — colder than Rome, colder than Madrid, colder than Dublin, all of which are considerably further north. Every figure below is measured at the capital's coordinates rather than averaged across the country, a distinction the last section returns to.

The biggest cluster is Atlantic-facing Europe: Dublin 5.3°C, London 4.2°C, Paris 4.1°C, Amsterdam 3.8°C, Berlin 2.4°C, Warsaw 2.1°C, Vienna 1.7°C, Stockholm -0.9°C, Reykjavík -1.5°C. Temperature does fall as you go north here, but the slope is remarkably gentle — climbing the 11 degrees of latitude from Dublin to Reykjavík costs only 6.8°C. Eleven degrees in the other direction from Seoul would land you in a different season entirely.

Southern Europe widens the gap. Lisbon (38.7°N) and Athens (38.0°N) sit at practically Seoul's latitude and average 13.2°C and 11.2°C in January, 15.1 and 13.1 degrees above it. Rome at 10.2°C, Tirana at 9.7°C, Madrid at 7.1°C, Andorra la Vella at 4.5°C, Budapest at 2.8°C and Bern at 1.4°C fill the space between.

Five more sit outside Europe: Tbilisi 4.9°C, Ankara 4.1°C, Tashkent 1.4°C, and then Beijing at -1.4°C and Washington D.C. at -1.5°C. Those last two are north of Seoul and beat it by only 0.5 and 0.4 degrees. That narrow margin is the clue.

Collect the capitals whose January mean matches or undercuts Seoul's and the list is short: Ottawa, Pyongyang, Seoul, Washington D.C., Beijing. Set Ottawa aside and every one of them clings to the eastern edge of a large continent. The capitals far to Seoul's north that still run warmer are, without exception, on a western seaboard or surrounded by ocean.

No amount of staring at the temperature column produces this explanation. Through winter a vast pool of cold air — the Siberian High — settles over inland Eurasia, and the cold, dry northwesterlies spilling off it run down the continent's eastern flank across the Korean peninsula and eastern China. Eastern North America draws on its own continental interior the same way. Western Europe and Iceland, meanwhile, meet westerlies that have crossed water warmed by the North Atlantic Current. At equal latitude, what decides the winter is where the wind has been.

Reading winter off a latitude works passably within Europe and badly in Korea, eastern China and the eastern United States. Seoul's January is genuinely harsh for where it sits, and the reason has nothing to do with how far south it is.

Seoul's annual range — the hottest month's high minus the coldest month's low — is 38.7°C, sixth of 53. Only Ottawa at 42.2°C, Tashkent at 41.6°C, Pyongyang at 39.0°C, Tehran at 38.9°C and Beijing at 38.7°C exceed it. That is an extreme position for a country usually filed under temperate four-season.

Against Reykjavík it is stark. Iceland's capital has an annual range of 17.8°C, under half Seoul's. Reykjavík wins January by 0.4 degrees and loses July by 16.7, averaging 11.7°C against Seoul's 28.4°C. The two cities differ less in how cold they get than in how far the year travels.

Jakarta marks the other extreme: Indonesia's annual range is 7.6°C, the smallest here. The distance between a city where one wardrobe lasts all year and a city that swaps its wardrobe twice fits inside that one figure.

Escaping a northern winter properly takes more than one good month. Filter for countries where all three of December, January and February average 18–27°C with under 150mm of monthly rain and eight of the 53 survive.

Five are in the southern hemisphere. Buenos Aires barely moves across the three months at 25.8°C, 25.7°C and 25.9°C, with Montevideo close behind at 22.8, 22.2 and 24.0. Santiago runs 21.8, 23.8 and 23.9 and collects a combined 3mm of rain over the whole quarter. Lima (19.8, 21.7, 23.5) and Canberra (19.1, 21.1, 20.6) sit at the cooler end. The other three are northern-hemisphere places whose winters are simply mild: Doha at 21.2, 18.3 and 18.9, Abu Dhabi at 23.0, 20.2 and 21.7, and Santo Domingo at 24.7, 24.7 and 24.8.

Relax the filter to a single month and the field widens to ten in January and ten in December, pulling in places like Bangkok, Phnom Penh and Hanoi that qualify in some months but not others. The three-month version is built for a long stay or a trip spanning the New Year; for a fortnight away, check the individual month instead.

Every temperature here comes from a single point: the capital's coordinates. The larger the country, the less that point represents it. Australia's 21.1°C in January is Canberra, not Cairns; the United States' -1.5°C is Washington D.C., not Miami. Chile stretches over 4,000km north to south, so reducing it to Santiago strains the exercise. For compact countries like Korea or Iceland the capital reading tracks the country closely.

Warmer also does not mean more pleasant. In early January Reykjavík gets roughly four to five hours of daylight against Seoul's nine and a half. Reykjavík wins on the thermometer and loses more than half the usable day. Add wind and cloud cover and the two Januaries diverge far more than the temperature column suggests. Temperature is the single axis this report covers.

Monthly temperature and rainfall for each country are on its detail page, and the comparison pages put any two of them side by side.