So, it happens on average every 150 years and that isn't a cycle in your book. That's fine for someone like yourself but for me I feel that we then need to redefine things like solar cycles and seasons which only happen on average as well. All in all, what the article describes sounds like a cycle to me.
The seasons happen for a known, cyclical reason. If it turns out that there's a first cause behind the ice melt, then it would be proper to refer to it as a cycle.