"It always rains a lot here, it's very cold and it's January and it feels like summer," said Bilbao resident Eusebio Folgeira, 81.
French tourist Joana Host said: "It's like nice weather for biking but we know it's like the planet is burning.
Scientists have not yet analysed the specific ways in which climate change affected the recent high temperatures, but January's warm weather spell fits into the longer-term trend of rising temperatures due to human-caused climate change.
"The record-breaking heat across Europe over the new year was made more likely to happen by human-caused climate change, just as climate change is now making every heatwave more likely and hotter," said Dr Friederike Otto, climate scientist at Imperial College London.
French national weather agency Meteo France attributed the anomalous temperatures to a mass of warm air moving to Europe from subtropical zones.