Holocene Climate Shift

As my readers know, I have given a lot of thought to the historical temperature record of the post Pleistocene Nonconformity era we call the Holocene. This era began with the mopping up of the vestiges of the preceding million year Ice Age that began with the closure of the Panama Isthmus. The almost total removal of the Polar ice cap produced a northern temperate climate regime that has typically varied about a half degree per century at most. We are rarely been forced to abandon huge tracts of farm land. The Holocene has been the true cradle of human emergence from its barbaric past.

This makes the understanding of temperature anomalies in the record very important. They push us to understand the more general nature of our climate engine. The recent era has seen a rough half degree increase in the northern Hemisphere over the past century. We have every reason to think that this is actually true. The fact that this is a continuing rebound from the chilling event of the little Ice age does enough to explain the shift. Other causes are so far an unnecessary conjecture.

There is exactly one major anomaly in the record that needs to be addressed. Why did the Bronze Age temperature regime abruptly end? We have been living in a post Bronze Age climate regime that is clearly a couple of degrees colder in the Northern Hemisphere that was true during the two thousand year Bronze Age.

Since it ended, we have a constant cycle of failed recoveries, punctuated by sharp reversals that create so called little ice ages. Somehow these reversals lower the temperature a degree or so and we then spend decades if not a century or two recovering. The chilling mechanism is not yet well understood but after watching the macroclimatic behavior of this past year, I would place my bets on the wind circulation system as more than capable of transporting enough heat around to mess up the system. It is just that it is unusual.

This is clearly not enough to explain the climate regime of the Bronze Age. We simply had more heat in the Northern Hemisphere for two thousand years.

I will make the following conjecture. During the Bronze Age, the Sahara Desert was created by mankind. The creation of the Sahara, released a huge amount of solar energy back into space. There was nothing on the ground capable of absorbing all that energy and turning it into atmospheric heat and plant material unable to escape easily to space. That is why the desert becomes so cold at night and so frightfully hot in the daytime. This meant that the Northern Hemisphere has had measurably less available heat for the past four thousand years or so.

An immediate corollary of this conjecture is that the full restoration of the Sahara and all Asian deserts generally will warm and moderate the climate of the Northern Hemisphere and hugely expand the agricultural potential of Eurasia.

This agricultural terrain was systematically destroyed be the advent of goats during the Bronze Age throughout this region. It is their nature to eat a plant to destruction and must be carefully controlled, an option never available in primitive agriculture.
I had previously speculated that perhaps the little Ice Age temperature declines were driven by volume changes in the ocean current systems. This may still have merit but I am much less inclined to support that conjecture now that the strength of the atmospheric circulatory system is much more apparent in northern latitudes.

Also we have had an apparent shift in the volume of the Gulf Stream without any visible effect on its climatic effect over the past fifty years. This means that the principal current is dragging a surface layer of warm water containing most of the heat into the Arctic and affecting climate that way while the varying driver current is doing its thing primarily out of harms way a little deeper.

I think that we have laid the last brick in fully understanding the modest climate variation experienced during the Holocene era. That is good news, because if we cannot reasonably understand our climatic baseline and run experiments against it, we end up talking rubbish.

That is what predictions of a new ice age are and even to a large degree anthropogenic warming when you understand that right now all variation is well within the anticipated variation from the well established baseline.

None of this excuses us from the proper use of good practice to sequester waste CO2. After all, I am predicting that the reforestation of the Eurasian Desert and much of the remaining Northern Hemisphere will raise the temperature of the Northern Hemisphere significantly and powerfully enhance agriculture. In other words, proper sequestration of CO2 will actually warm the planet, but that is a good thing.

No comments:

Post a Comment