Copenhagen · September · relief from the heat

Coolest places to go from Copenhagen in September

In September, the coolest well-known place within 15 hours of Copenhagen is Reykjavik, Iceland, 9.0 °C cooler than Copenhagen and 6.3 h sun a day, about 6h 18m each way by air. Without flying, it is Östersund, Sweden, 5.8 °C cooler than Copenhagen, about 14h 6m each way by train, for about 21× less carbon (24.9 kg CO₂e return against 529 kg).

The 10 coolest places within 15 hours of Copenhagen

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.

Reykjavik, Iceland9.0 °C cooler · 6.3 h sun a day · 3.5 mm rain a day · sea 10.8 °Cair ≈ 6h 18m · 529 kg CO₂e return
Tromsø, Norway6.8 °C cooler · 4.9 h sun a day · 5.2 mm rain a dayair ≈ 5h 36m · 399 kg CO₂e return
Östersund, Sweden5.8 °C cooler · 7.7 h sun a day · 2.6 mm rain a dayrail ≈ 14h 6m · 24.9 kg CO₂e return
Bodø, Norway5.6 °C cooler · 5.2 h sun a day · 6.6 mm rain a day · sea 13.0 °Cair ≈ 5h 12m · 326 kg CO₂e return
Rovaniemi, Finland5.3 °C cooler · 6.0 h sun a day · 3.5 mm rain a dayair ≈ 5h 24m · 349 kg CO₂e return
Trondheim, Norway4.7 °C cooler · 7.0 h sun a day · 5.8 mm rain a dayrail ≈ 14h 36m · 25.7 kg CO₂e return
Sundsvall, Sweden4.2 °C cooler · 8.4 h sun a day · 2.3 mm rain a day · sea 14.2 °Crail ≈ 12h 18m · 23.4 kg CO₂e return
Luleå, Sweden4.2 °C cooler · 7.7 h sun a day · 2.4 mm rain a day · sea 14.3 °Cair ≈ 5h 6m · 306 kg CO₂e return
Dundee, United Kingdom4.1 °C cooler · 7.7 h sun a day · 2.0 mm rain a day · sea 13.9 °Cair ≈ 4h 48m · 243 kg CO₂e return
Glasgow, United Kingdom3.5 °C cooler · 7.2 h sun a day · 3.4 mm rain a dayair ≈ 4h 54m · 264 kg CO₂e return

Without flying

The coolest places the train reaches within 15 hours. Östersund is 5.8 °C cooler for 24.9 kg — about 21× less carbon than flying to Reykjavik.

Östersund, Sweden5.8 °C cooler · 7.7 h sun a day · 2.6 mm rain a dayrail ≈ 14h 6m · 24.9 kg CO₂e return
Trondheim, Norway4.7 °C cooler · 7.0 h sun a day · 5.8 mm rain a dayrail ≈ 14h 36m · 25.7 kg CO₂e return
Bergen, Norway4.4 °C cooler · 6.5 h sun a day · 8.8 mm rain a day · sea 15.6 °Crail ≈ 11h 48m · 19.9 kg CO₂e return
Sundsvall, Sweden4.2 °C cooler · 8.4 h sun a day · 2.3 mm rain a day · sea 14.2 °Crail ≈ 12h 18m · 23.4 kg CO₂e return
Ålesund, Norway4.2 °C cooler · 6.9 h sun a day · 7.7 mm rain a day · sea 14.6 °Crail ≈ 14h 6m · 24.8 kg CO₂e return
Umeå, Sweden3.9 °C cooler · 7.7 h sun a day · 2.5 mm rain a day · sea 14.2 °Crail ≈ 14h 48m · 29.6 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 Copenhagen in September within 15 hours is Reykjavik, 9.0 °C cooler, costing 529 kg CO₂e return. The lowest-carbon option is Borås at 6.7 kg — 79× less carbon, for 6.6 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.

Where they are. Solid lines are rail or ferry, dashed are flights, from Copenhagen. Pick one to compare.

By rail or ferry By air

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

September from Copenhagen — 6 destinations on the frontier, 4 without flying.
Destination	How	CO₂e return	Temp	Sun/day	Rain/day	Journey
Borås, Sweden	Rail	6.7 kg	14.1 °C	8.6 h	3.4 mm	5h 18m
Oslo, Norway	Rail	14.3 kg	13.3 °C	7.3 h	3.4 mm	9h
Lillehammer, Norway	Rail	18.2 kg	12.0 °C	7.0 h	4.6 mm	10h 54m
Östersund, Sweden	Rail	24.9 kg	10.7 °C	7.7 h	2.6 mm	14h 6m
Tromsø, Norway	Air	399 kg	9.7 °C	4.9 h	5.2 mm	5h 36m
Reykjavik, Iceland	Air	529 kg	7.5 °C	6.3 h	3.5 mm	6h 18m

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 Östersund (24.9 kg, 5.8 °C cooler) to Tromsø (399 kg, 6.8 °C cooler) buys 1.0 °C more relief from the heat for an extra 374 kg — 374 kg of CO₂e per degree. That single step is the most expensive relief from the heat on the whole curve.

The pick of them

BoråsSweden6.7 kg CO₂e return14.1 °C · 8.6 h sun · 5h 18m by railmild and bright

ÖstersundSweden24.9 kg CO₂e return10.7 °C · 7.7 h sun · 14h 6m by railmild and bright

ReykjavikIceland529 kg CO₂e return7.5 °C · 6.3 h sun · 6h 18m 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 Copenhagen

September from elsewhere

Photo credits

Borås: Amjad Sheikh, CC BY-SA 3.0, via Wikimedia Commons
Östersund: Lars Falkdalen Lindahl (User:Njaelkies Lea), CC BY-SA 3.0, via Wikimedia Commons
Reykjavik: Hedwig Storch, CC BY-SA 3.0, via Wikimedia Commons
Tromsø: Diego Delso, CC BY-SA 4.0, via Wikimedia Commons
Bodø: Røed 20:41, 24 July 2006 (UTC), CC BY-SA 2.5, via Wikimedia Commons
Trondheim: Åge Hojem/Trondheim Havn from Trondheim, Norway, CC BY-SA 2.0, via Wikimedia Commons
Sundsvall: User:Ö1thpe0807 (image 1), User:I99limpan (image2), User:Larskallin (image3), Hans Lindqvist (image 4-5), Calle Eklund (, CC BY-SA 3.0, via Wikimedia Commons
Luleå: Andreas Harnemo, CC BY-SA 3.0, via Wikimedia Commons
Dundee: File:442 dundee header.png (Tay Bridge and RSS Discovery images):- Original: PlutosAcademy File:V&A Dundee Near Completi, CC BY-SA 4.0, via Wikimedia Commons
Glasgow: 瑞丽江的河水, CC BY-SA 4.0, via Wikimedia Commons
Bergen: W. Bulach, CC BY-SA 4.0, via Wikimedia Commons
Ålesund: Holger Uwe Schmitt, CC BY-SA 4.0, via Wikimedia Commons
Umeå: Jonipoon, CC BY-SA 4.0, via Wikimedia Commons

Questions

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

Reykjavik, Iceland, at 9.0 °C cooler. Reaching it emits 529 kg CO₂e return, travelling 6h 18m each way by air (modelled).

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

Yes. Östersund reaches 5.8 °C cooler and is reachable by rail or ferry in 14h 6m (modelled), emitting 24.9 kg CO₂e return — though Reykjavik is cooler still, if you fly.

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

529 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.