Wednesday, December 5, 2007

The Sargasso Sea as a proxy

As I have posted earlier, there is a natural tendency for the Northern Hemisphere to warm while there is an equally natural tendency for the Southern Hemisphere to cool. The 2000 year extended warming of the Bronze Age is the stabilized result of this tendency. This means that for the Northern Hemisphere, that the only important question is how did it cool off in the first place.

The afore mentioned tendency is simply driven by the fact that the bulk of continental land surrounds an Arctic Ocean that is able to prevent the production of an Ice cap, while we have a mirror image in the Antarctic. It is actually an amazing arrangement that will now be stable for millions of years since the only Ice cap in the Antarctic will continue to calve surplus ice into the ocean. In fact it looks like an extraordinary coincidence and I do not ordinary coincidences.

And then we have the coincidence of the Maunder sunspot minimum coinciding with the cyclic temperature low that gave us the Little Ice Age. My own thoughts are this is not too much of a coincidence since it would have simply worsened a natural condition. If this one hundred year event had nailed it to coincide with a peak in the apparent 1000 year cycle, then that would have been highly unusual. Instead it hit while the Northern climate was likely already past its cooling phase and simply deepened and delayed the recovery part of the projected cycle.

The point made is that the loss of that 0.1 percent solar sunspot radiation for a hundred years was enough create the so called Little Ice Age because it actually acted on an already cooling Northern climate. If it were to happen now, the effect would be a great deal less than in 1600 AD.

One aspect of global warming that was not been talked about is the recent findings of solar scientists of three separate mechanisms by which the sun could warm or cool the Earth, the most important of which is an ongoing increase in ultra violet light. It appears to have led the observed climatic effects for the past several hundred years, although I do wonder how this data match could be possibly reliable. It would be actually nice if solar variation was sufficient too make all the observed changes. It is certainly the big engine compared to all other mechanisms.

Since the sunspot cycle is hitting a minimum this year, it is reasonable that the next five years should be simply cold as the effect catches up. I am not that optimistic but we may have a standstill in the Arctic for five years, although during this last cycle there was ongoing ice loss. In fact since the cycle is ten years in length and the previous cycle maxima was in 1998 we may face a surprisingly good year for sea ice removal in 2008.

That brings us back to the most important climate driver of all. That is the temperature of ocean currents and as important the individual seas. Remember that a sea needs to be properly defined as a body of water that is slowly rotating with perimeter currents interacting with other seas to exchange energy and salinity. The South Atlantic gyre is one as is the Arctic. The point is is that the temperature ranges in the Sargasso Sea and in the Caribbean Sea were both 2 to 3 degrees Celsius cooler than today during the Little Ice age.

This is a huge difference that may have been effected by variations in solar energy. The problem is that my back of the envelope calculations tell me that these variations are actually way too weak by a factor of at least ten. That puts us back into the antarctic cooling engine. As the Antarctic cold zone expands, it is able to stimulate an increase in mixing with adjacent seas and this strongly increases current flow heading north almost as a pulse. This happens in both the Pacific and the Atlantic.

The problem for forecasting is that this mechanism is going to lead or lag other climatic effects by decades. The north will progressively warm while slowly pushing the triggers to the switch point. When the influx of cold water comes, there will still be plenty of inertia in the climate and it will take a long time for the impact to assert itself.

In point of fact, using the Sargasso Sea as a proxy, it appears that we had a 1000 year decline from the 1000 BC to 0 AD, a 1000 year advance from 0 AD to 1000 AD and a 1000 year decline from 1000 AD to a couple of hundred years ago. The variation around that curve was at least one degree per century which is exactly what we are experiencing.

And as I have been observing, we are about to break into warm side of the curve above which the arctic seas will clear. Once the Arctic is clear a warm north will be stable for a while.

Again using Sargasso Sea proxy, it is obvious that although we have entered an uptrend, we are due for a reversal within that uptrend that could last a century. If we are lucky, we will clear the Arctic before that happens and we will have and extended warm spell.

In the meantime it would be good to develop a similar database for every sea on Earth so that we can actually map historic global sea temperatures which will then allow us to properly model historic climate conditions.

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