Water, water everywhere ... it kind of makes one think

I had a thought experiment recently about what the world would be like if water behaved more normally and was denser as a solid than as a liquid. This idea isn’t new, but most of the conclusions end up being a terse “the oceans would freeze and everything would die.” I’d like to be a little more cautious in my consideration of this hypothetical.

First, ice freezes as it does because of the dipole effect of the H2O molecule and its ability to form strong hydrogen bonds that allow for the formation of a peculiar lattice which results in its abnormal density relative to its liquid state. Proposing that water instead became denser as it freezes requires a modification of the molecule. Nonetheless, let us set that aside and say that things just turned out that way (with all other laws of nature turning out the same). What would this mean?

The most obvious issue to address is the effect on oceans and lakes. Presuming that water behaves more normally and is denser as a solid than a liquid, one could extend this “normal” quality to the consequence of pressure and require that as pressure increases the melting temperature also increases. This is contrary to the current state of increasing pressure lowering melting point, allowing ice skaters to glide and glaciers to drift. Anyway, as surface temperatures on Earth drop ice would begin to form on the surface of bodies of water and start to sink (since water is a better insulator than air ice would tend to form first at the water-air boundary). As the ice sinks, more water becomes exposed to the air and changes phase which continues the process. Eventually a significant portion of the water in lakes and oceans would become ice, effectively freezing from the bottom up because of the increased pressure of the water above it requiring a higher ambient temperature to melt the ice. In the warmer months there would likely be a layer of water near the surface floating on a layer of ice which may or may not be suspended on pockets of water due to vents in the crust emitting high temperatures. If instead an increase in pressure contributed to melting ice as it is now, I expect a significant layer of ice would form both in lakes and oceans at the depth beyond which the ice would begin to melt due to increased pressure. In either case, the layer of ice would be significantly thicker than currently forms which would take longer to melt and would likely create a false bottom to bodies of water made of ice that would be perpetually tens to hundreds of meters thick.

This would have damning consequences to many things. Ocean currents would be dramatically affected which would change the planet’s climate and cause upper latitudes to stay colder longer. It is also likely that since more water would be trapped in a solid state there would be less rain to continue the water cycle, further reducing water supply in lakes and rivers. The surface temperature of both water and earth would also be reduced, which would possibly prohibit the growth of plant life beyond mosses and lichens, to say nothing of the effect on fish and animal life. Finally, the biggest problem would be the effect on the atmosphere; since algae would likely not form due to the consistent freezing and thawing at or near the surface, the oxygenation of the atmosphere would take significantly longer to get to the level we are today, and perhaps it would never reach the current state.

The real conclusion is that no matter how you slice it, humanity would not exist if not for the simple matter of water decreasing in density when it freezes. Indeed, I doubt any complex land dwelling being would ever develop simply because of the lack of food and concentrated levels of carbon dioxide in the air. It’s interesting how a seemingly inconsequential fact of life is actually vital to its development.