I've got a background in this field and I am very surprised to see this published in Nature. The model presented is purely statistical with no representation of the underlying physics. When we are dealing with a phenomenon that is driven by well-understood physical laws (e.g. geophysical fluid dynamics, radiation physics etc) then these physical models are the most reliable basis for prediction.
When I say physical models here by the way I'm referring to physically-based mathematical models as well as numerical models.
It seems that the authors have done a good job in developing their model. My issue is with Nature deciding to publish it. If this paper was not published in Nature it would receive little attention within or without climate science - in fact many such statistical models are published each year without much comment. However, Nature have published a paper that I think many ocean scientists would feel draws dramatic conclusions from a weak basis but will now inevitably draw much more attention than more insightful papers.
MIT professor Carl Wunsch accused Nature in 2010 of near-tabloid science with a tendency towards sensational papers built on weak foundations. However, I've felt that Nature's choice of publications on climate in recent years has been high quality. This paper feels like a big step-down from that standard.