0xCarbon
Barcelona · September · relief from the heat

Coolest places to go from Barcelona in September

In September, the coolest well-known place within 15 hours of Barcelona is Reykjavik, Iceland, 14.0 °C cooler than Barcelona and 6.3 h sun a day, about 7h 30m each way by air. Without flying, it is La Chaux-de-Fonds, Switzerland, 7.4 °C cooler than Barcelona, about 10h 42m each way by train, for about 34× less carbon (21.7 kg CO₂e return against 745 kg).

The 10 coolest places within 15 hours of Barcelona

Ranked on relief from the heat in September alone, among well-known places (a Wikivoyage travel guide and at least 40,000 Wikipedia readers a year), one per area and at most three per country. The carbon is shown, not used to choose: the list further down is the other question, how much relief from the heat each extra kilogram buys.

  1. Reykjavik, Iceland14.0 °C cooler · 6.3 h sun a day · 3.5 mm rain a day · sea 10.8 °Cair ≈ 7h 30m · 745 kg CO₂e return
  2. Tromsø, Norway11.8 °C cooler · 4.9 h sun a day · 5.2 mm rain a dayair ≈ 7h 54m · 827 kg CO₂e return
  3. Östersund, Sweden10.8 °C cooler · 7.7 h sun a day · 2.6 mm rain a dayair ≈ 6h 54m · 643 kg CO₂e return
  4. Bodø, Norway10.6 °C cooler · 5.2 h sun a day · 6.6 mm rain a day · sea 13.0 °Cair ≈ 7h 30m · 748 kg CO₂e return
  5. Rovaniemi, Finland10.3 °C cooler · 6.0 h sun a day · 3.5 mm rain a dayair ≈ 7h 42m · 791 kg CO₂e return
  6. Trondheim, Norway9.7 °C cooler · 7.0 h sun a day · 5.8 mm rain a dayair ≈ 6h 48m · 631 kg CO₂e return
  7. Sundsvall, Sweden9.2 °C cooler · 8.4 h sun a day · 2.3 mm rain a day · sea 14.2 °Cair ≈ 6h 54m · 639 kg CO₂e return
  8. Luleå, Sweden9.2 °C cooler · 7.7 h sun a day · 2.4 mm rain a day · sea 14.3 °Cair ≈ 7h 30m · 746 kg CO₂e return
  9. Dundee, United Kingdom9.1 °C cooler · 7.7 h sun a day · 2.0 mm rain a day · sea 13.9 °Cair ≈ 5h 48m · 432 kg CO₂e return
  10. Glasgow, United Kingdom8.5 °C cooler · 7.2 h sun a day · 3.4 mm rain a dayair ≈ 5h 42m · 421 kg CO₂e return

Without flying

The coolest places the train reaches within 15 hours. La Chaux-de-Fonds is 7.4 °C cooler for 21.7 kg — about 34× less carbon than flying to Reykjavik.

  1. La Chaux-de-Fonds, Switzerland7.4 °C cooler · 9.2 h sun a day · 3.5 mm rain a dayrail ≈ 10h 42m · 21.7 kg CO₂e return
  2. Memmingen, Germany6.5 °C cooler · 9.6 h sun a day · 3.5 mm rain a dayrail ≈ 14h 24m · 28.6 kg CO₂e return
  3. Bern, Switzerland6.1 °C cooler · 9.6 h sun a day · 3.6 mm rain a dayrail ≈ 11h · 22.1 kg CO₂e return
  4. Milton Keynes, United Kingdom5.9 °C cooler · 7.6 h sun a day · 3.6 mm rain a dayrail ≈ 14h 24m · 39.5 kg CO₂e return
  5. Oxford, United Kingdom5.8 °C cooler · 7.7 h sun a day · 4.1 mm rain a dayrail ≈ 14h 36m · 40.2 kg CO₂e return
  6. Southampton, United Kingdom5.4 °C cooler · 8.0 h sun a day · 3.8 mm rain a dayrail ≈ 15h · 42.6 kg CO₂e return

≈ is the model's estimate (air times include getting to and through the airport); ✓ is a rail journey checked against a real timetable, with the date it was checked. Temperatures are historical daily means for 2023–2024, averaged across day and night, so afternoons run warmer.

The low-carbon trade-off

The coolest place you can reach from Barcelona in September within 15 hours is Reykjavik, 14.0 °C cooler, costing 745 kg CO₂e return. The lowest-carbon option is Huesca at 6.7 kg — 111× less carbon, for 11.5 degrees less relief from the heat.

Every destination here is on the efficiency frontier: nowhere else this site covers is both cooler in September and lower in carbon. Anything a better option beats outright has been left out.

HuescaReykjavik
Where they are. Solid lines are rail or ferry, dashed are flights, from Barcelona. Pick one to compare.
Carbon against relief from the heat, September, departing Barcelona. Journeys of up to 15 hours each way.10 destinations. Lowest carbon Huesca at 6.7 kilograms and 2.5 °C cooler; best for relief from the heat Reykjavik at 745 kilograms and 14.0 °C cooler. Huesca · 6.7 kgStirling · 427 kgKristiansund · 614 kgReykjavik · 745 kg

By rail or ferry By air

Carbon against relief from the heat, September, departing Barcelona. Journeys of up to 15 hours each way.

What the 15-hour limit costs: at this budget Buxton can only be reached by air — 341 kg CO₂e, in 5h 18m. Allow up to 24 hours and the train does the same journey for 52.0 kg in 16h 42m — 7× less carbon for 11h 24m more travelling.

September from Barcelona — 10 destinations on the frontier, 5 without flying.
DestinationHowCO₂e returnTempSun/dayRain/dayJourney
Huesca, SpainRail6.7 kg19.0 °C10.2 h4.8 mm4h 30m
Teruel, SpainRail8.8 kg18.0 °C10.5 h1.3 mm5h 36m
Rodez, FranceRail9.8 kg16.3 °C9.4 h3.1 mm6h 12m
Soria, SpainRail11.4 kg15.3 °C10.1 h2.3 mm5h 24m
La Chaux-de-Fonds, SwitzerlandRail21.7 kg14.1 °C9.2 h3.5 mm10h 42m
Buxton, United KingdomAir341 kg12.8 °C7.1 h3.9 mm5h 18m
Stirling, United KingdomAir427 kg12.3 °C7.2 h3.3 mm5h 48m
Kristiansund, NorwayAir614 kg11.6 °C7.1 h6.5 mm6h 48m
Östersund, SwedenAir643 kg10.7 °C7.7 h2.6 mm6h 54m
Reykjavik, IcelandAir745 kg7.5 °C6.3 h3.5 mm7h 30m

Warm is not the same as pleasant, which is why sunshine and rainfall are shown alongside temperature. All three are ERA5 monthly means for 2023–2024.

Where the curve breaks

The frontier is gentle until it isn't. Going from Stirling (427 kg, 9.2 °C cooler) to Kristiansund (614 kg, 9.9 °C cooler) buys 0.7 °C more relief from the heat for an extra 188 kg — 268 kg of CO₂e per degree. That single step is the most expensive relief from the heat on the whole curve.

The pick of them

HuescaSpain6.7 kg CO₂e return19.0 °C · 10.2 h sun · 4h 30m by railwarm but wetLa Chaux-de-FondsSwitzerland21.7 kg CO₂e return14.1 °C · 9.2 h sun · 10h 42m by railmild and brightReykjavik, IcelandReykjavikIceland745 kg CO₂e return7.5 °C · 6.3 h sun · 7h 30m by aircool

The same month, asked differently

September answers differently depending on what you are after, and the lists genuinely diverge: the brightest places are not the hottest, and in summer the useful question stops being where is warm at all.

Where to stay in Reykjavik

Places to stay in Reykjavik, Iceland, on a live map. Prices and availability come from Stay22 and its booking partners.

Search places to stay in Reykjavik →Opens the booking search in a new tab. Same partners as the map below.

Affiliate disclosure. A booking made through this map may earn 0xCarbon a commission, at no extra cost to you. It changes nothing above it: the emissions figures come from UK Government conversion factors and are computed before anyone is paid anything.See the method.

Other months from Barcelona

September from elsewhere

Photo credits

Questions

Where is the coolest place to go from Barcelona in September?

Reykjavik, Iceland, at 14.0 °C cooler. Reaching it emits 745 kg CO₂e return, travelling 7h 30m each way by air (modelled).

Can I get somewhere cool from Barcelona in September without flying?

Yes. La Chaux-de-Fonds reaches 7.4 °C cooler and is reachable by rail or ferry in 10h 42m (modelled), emitting 21.7 kg CO₂e return — though Reykjavik is cooler still, if you fly.

How much carbon does a return trip from Barcelona to Reykjavik produce?

745 kg CO₂e for one person, return, by air. That uses the UK Government's 2026 conversion factors, including radiative forcing for flights.

Carbon uses UK Government (DESNZ/DEFRA) 2026 conversion factors applied to great-circle distance, with radiative forcing included for flights. Rail journey times are modelled estimates, not timetabled services. Full method · download the data.