A few years ago, when I was trying to explain what led to the ice-age, I began with an expectation that I could include CO2 as at least explaining part of the cycle … but it turned out that when I looked in detail, that dramatic changes in temperature had no relationship to CO2 … and as problematic, the change in CO2 lagged temperature.

This left me with a problem, because without a plausible form of positive feedback sufficiently large to induce a catastrophic decline into the ice-age, I could not explain the ice-age cycle.

One possibility I did consider was a change in the Hadleigh cell structure from the current 3 south, 3 north to either 1+1, or 5+5. The reason for this, is that the equator is always the hottest zone so sees rising air, and the poles are colder, so see descending air. The current three zone structure is created by descending air over the latitude of the Sahara (making it dry) and rising air over the latitude of the UK (making us wet).

This creates a potential mechanism to shut of the current three cell structure. The North Atlantic drift (wrong termed the Gulf Stream), is the dominant current that brings warm water from the south up toward Britain. (There is also another and much smaller current that enters the Arctic ocean which often gets talked about as it can shut off due to changes in ice, but it is really quite insignificant).

The problem with shutting off the 3 cell structure, is that North Atlantic drift and the equivalent current in the Pacific, supply much of the energy to create the rising cell structure  at the UK that maintains the 3+3 cell structure. But the 3+3 structure also creates the northward going trade winds which drive the North Atlantic drift (which get diverted by the earth’s spin so in the UK our predominant winds are from the SW). So, the 3+3 structure is maintained by the North Atlantic Drift, which is driven by the northerly winds by the 3+3 structure. So, if either the cell structure of the current were to cease, then the other would also cease and this could permanently “latch” the world’s climate into a new structure. That could explain the almost “two state” climate we see between “ice-age” and “interglacial”, but it doesn’t explain what the new state might be, nor how it makes the world cooler.

Proposal

I guess it was looking out the window, waiting for the day to warm so that I could do my car bearings, that started me thinking about which clear days are colder and how High pressure results in cooler conditions. I then started thinking about what would happen if we got a long period of high pressure over the UK in the winter: the ground would freeze, although we wouldn’t get as much precipitation, what we would get would be snow, and that would start to accumulate. And that in turn changes the colour of the ground so that more sunlight gets reflected. That is all well known. But then I started thinking about the air movement patterns. Instead of air moving generally along the “Hadleigh cells”, when we get High pressure over land, the air descends over land and then pushes out onto the sea. And, if the land were ice-covered, or covered in deserts and so reflecting more sunlight so getting less heat than the sea there could possibly develop a permanent wind pattern of descending air over the land, and rising air over the sea.

Importantly, this kind of wind pattern must occur, because globally, what we see in the ice-age period is that much of the land turns to desert. That indicates an absence of moist onshore winds, which means the predominant wind direction must change to be offshore.

Also importantly, this explains why the ice-age can be “latched in”, whilst the solar input hardly changes. The land becomes colder … partly because of the higher reflectance of heat from the ice sheets and deserts that form, but partly because the predominant movement of air is that of cold-dry descending air over land. Conversely, over the sea the air must be ascending, so here we have warm, moist ascending air, which undoubtedly means a lot of rain … but the rain is occurring over the sea and not the land. So, globally the temperature could be very similar … it’s just colder than now over land, and warmer over the sea. Likewise, the rainfall could be very similar, but in the ice-age, it predominantly occurs over sea.