Researchers say heatwaves of the kind currently being seen in northern Europe have become twice as likely due to climate change.

Scientists from the World Weather Attribution team said Friday they have compared observations and forecasts for the Netherlands, Denmark and Ireland with historical records going back to the early 1900s. They concluded the likelihood of three-day stretches of extreme heat in those areas has increased at least two-fold.

The group, which works to determine if there’s a link between weather phenomena and climate change, said current temperatures further north are so unusual there’s not enough data to predict their future likelihood.

Erich Fischer, an expert on weather extremes at ETH Zurich in Switzerland who was not involved with the study, said the authors use well-established methodology and “their estimates may even be rather conservative.”