Canada’s renowned Rideau Canal Skateway, the world’s largest natural ice skating rink, will not open this season for the first time due to a lack of ice, its operator said on Friday, blaming the closure on climate change.

The 7.8 km (4.9 mile) Rideau Canal Skateway, first opened over 50 years ago, is part of a UNESCO World Heritage Site in Canada’s capital city Ottawa that is a top attraction for skating enthusiasts seeking outdoor thrills during Canada’s usually biting cold winters.

The National Capital Commission (NCC), which maintains and operates the Skateway, said that although they have been assessing and preparing for the impacts of climate change, their efforts to open the rink this season have “come to an end.”

“This year taught us a great deal about the effects of milder winters on the Skateway,” the commission said in a statement on Friday.

The NCC has previously said it can only open when the ice is at least 12 inches (30 cm) thick, for which there must be 10 to 14 consecutive days of temperatures between -20 Celsius and -10 Celsius (-4 and 14 degrees Fahrenheit).

In Ottawa the mean temperature in January was -5.9 Celsius (21.4 Fahrenheit), according to the Weather Network, well above the -10.3C average.

Temperatures this year are being driven by the La Nia weather phenomenon, while climate change has made mild winters more likely than they were a few decades ago, said Doug Gillham, manager of the Weather Network’s forecast centre.

The NCC and the Standards Council of Canada have commissioned a climate change risk assessment to understand the impact of climate change on the Skateway.

Under the scenario of moderate emissions, “the NCC should prepare for seasons with less than 40 days of skating approximately 50% of the time,” it says.

The average season has been 50 days — and went up to 95 days in the early 1970s, according to the NCC website.

“Even the cold of the last 24 hours couldn’t make up for this winter’s higher-than-average temperatures, snow and rain, which contributed to a thin and porous ice surface,” the NCC said on Twitter.