“A Farewell to Ice” by Peter Wadhams: Review

I have just finished readingA Farewell to Ice” by Peter Wadhams. And I found it a deeply uncomfortable read.

It can be considered as a first-hand account of the Arctic Death Spiral summarised in the figure below.

Click for a larger version. The Arctic Death Spiral – copied from this link. Proceeding clockwise from the top, each line charts the estimated volume of Arctic Sea Ice in thousands of cubic kilometers for a specific month of the year. The centre corresponds to no sea ice, and the maximum radius corresponds to 30,000 cubic kilometers. The precise date at which the Arctic will be ice-free in September (black line) is not clear, but you will likely live to see it happen.

Sometimes when reading a book, one does not learn any basic new facts. This can serve as confirmation that’s one’s prior understanding was (broadly) OK.

Contrariwise, one sometimes learns a fact so basic that one realises the depth of one’s prior ignorance.

Significantly, in this book I learned that the formation of Arctic Sea-Ice is MUCH more complicated than I had hitherto appreciated.

How Seawater Freezes

Firstly, when seawater cools, it does not – like freshwater – exhibit a density a maximum at around 4 °C. How did I not know that?

Click for a larger version. The density of pure water as a function of temperature. The maximum density occurs approximately 4 °C above the freezing point.

This density anomaly is small – amounting to just 0.02% – but it plays a critical role in how open water freezes in lakes.

  • Imagine that the air above the water is very cold – say -10 °C – but that the lake water is initially warm, say + 10 °C.
  • The cold air cools the surface water which consequently becomes denser and sinks. As it sinks it lowers the temperature deeper in the lake.
  • But when the surface water cools below 4 °C, it becomes less dense and so floats at the surface. When this happens the surface layer freezes quickly, but most of the lake remains at 4 °C.
  • Hence freshwater fish are not frozen each winter.

But in water with a salt content higher than 2.47% this density maximum does not occur. Consequently, seawater – with a typical salinity of around 3.3% – cools in quite a different way to fresh water.

In seawater, the cold air can cool the entire water column down to the freezing temperature which – for saltwater – is depressed to around -1.8°C.

But this analysis only applies to still water: the action of waves on freezing water is complex and can give rise to many different structures in sea ice, including the fascinating ‘pancake’ ice.

And ‘piles’ of ice on top of the ice sheet arising from wind-driven collisions between different sections can act effectively as ‘sails’ on top of the ice.

And below these ‘sails’, equivalent ice structures develop which can act as ‘keels’, dramatically affecting sensitivity to sea currents and grounding the ice in shallow waters.

Overall, I learned that the apparently simple process of ‘water freezing’ is much more complex than I had appreciated. And significantly, I understood that accounting for this complexity was important if models of the processes were to be realistic.

The Wider Context

Peter Wadhams’ continuing fascination with the details of how sea-ice freezes and melts is evident in this book. But his fascination now evokes the same sadness as zoologists studying species which they know will soon be extinct: the behavioural details are fascinating but the more one understands, the greater the tragedy of their inevitable loss.

Peter Wadhams points out that when he began studying the polar regions in the 1970’s, it was generally accepted that the oceans were an unchanging environment, there to be mapped and studied.

And reading his accounts of his early adventures, I could share his sadness, shock and eventual horror at finding that the polar ecosystem was disappearing before his eyes (and other instruments).

Given his knowledge of the complexities of sea-ice formation it is perhaps understandable, but concerning nonetheless, that he is sceptical of the predictions of climate modelers who expect that summer sea-ice will remain for many decades. His view is that “summer’s lease has all too short a date“.

But whoever is correct, the state of the Arctic Ocean in the middle of this century is clear – there will be clear water at the North pole for several months of the year.

And so…

The book points out that the loss of sea ice (and snow cover on nearby land) affects the Earth’s overall albedo so much that it will be equivalent to an additional 50% of the warming caused by carbon dioxide emissions.

And that even if we reduced carbon dioxide emissions to zero overnight (which will not happen) this albedo warming would continue as long as the ice was gone – probably for centuries.

He stresses the importance of keeping the Arctic frozen both to reduce the overall warming, to prevent methane emissions, and to stabilise climate patterns in the Northern hemisphere.

He thus calls for geo-engineering (by low-level cloud formation) to re-freeze the Arctic now and buy time for longer term solutions.

I am generally a geo-engineering sceptic, but with regard to the Arctic, I found it difficult to disagree.

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