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Thursday, March 22, 2012

Pulsating climate

This is a pure bit of speculation.  If true, climate change will result, at least for the transition period, in very cold winters in America, Canada and Eurasia and very hot summers.  First a few facts (or at least accepted theories).

The Gulf Stream which brings warm water along the surface of the ocean from Florida towards the North Atlantic is powered primarily by the freezing out of fresh water ice from sea water in the Arctic and North Atlantic oceans.  Left behind is cold, saltier water which sinks and flows south along the bottom of the ocean.  Water is pulled north to replace this water.

The water which is being pulled northward is saltier than deeper water because of evaporation in the tropics but doesn't sink because it is warmer.  As it flows north, it cools and at some point is heavy enough to sink.  This positive feedback adds more power to the Gulf Stream.

As sea ice (and land ice for that matter) melts, it freshens the surface water in Northern latitudes and so when freezing starts, it will take longer before the resulting water is salty enough to sink. A big influx of fresh water into the North Atlantic should weaken the push that powers the Gulf Stream.

Ice is and insulator.  If you have open water in contact with cooler air, the water gives up its heat to the air, sinks and warmer deeper water replaces it.  The heat exchange between open water and the air is large and heat is being replaced on the surface by convection.  Once you have a cover of ice this convective process is greatly slowed.  Heat has to pass through the ice into the air in order to cool the water in contact with the bottom of the ice.  The thicker the ice the greater the "R" value of the ice.  ie, the slower the flow of heat between water and air.

As climate change continues, the time of net melting becomes earlier* and the time at which freezing exceeds melting is later.    The freezing period shortens, the melting period lengthens.  Here is where the speculation starts.

*Oddly enough over the past few years, the date at which melting starts has been getting later.

I wonder how long the delay is between the start of freezing and hence the sinking of salty water and the increase in flow of the Gulf Stream.  There should be a couple of factors in play here.  First it is a huge body of water to get moving with huge inertia so there should be a delay between push and move.  Think of a huge weight on one of those frictionless pads when you start to push it.  At first the motion is barely perceptible but builds up as you continue pushing.  Similarly, stop pushing and it takes the weight a long time to stop moving.

Secondly, it takes time for the warm salty water from the Florida region to move far enough north on the weakened Gulf Stream where it can cool enough to sink and add it's power to the Gulf Stream.

What strikes me as possible, is as the period of freezing shortens and the period of melting lengthens, we could reach a point where the push (cold salty water sinking) and the result (the Gulf Stream getting up to speed) could be 6 months out of sinkronicity.  We would end up with  a fast flowing Gulf Stream in the summer bringing warm water to the North Atlantic along with warm temperatures and, probably, heavy rain followed by a stalled Gulf Stream in Winter giving us really harsh winters.  Harsh winters would result in lots of freezing of fresh water ice from sea water, giving a push to the Gulf Stream.  It's effect would be felt next summer.

For those who suggest that this will lead to another ice age, remember, it doesn't matter how much snow falls in the winter or how cold it is.  An ice age can only start if the snow last through the summer.  In the above scenario, no snow would last through the summer.  In fact, the remaining glaciers should melt away with all the bad consequences this would bring.

Does anyone know if the flow of the Gulf Stream pulsates in any sort of annual cycle at present.

Post script:   A thought just occurred to me.  During this period of transition to a warmer climate in which the Arctic becomes largely ice free in the fall but freezes during the winter, the push to the Gulf stream should be shorter but sharper.  Clearly the ice starts to freeze later than previously but without a thick cover of ice, the transfer of heat to the atmosphere and the radiation of heat into space is more rapid.  It is possible that the rate of freezing and hence the rate of production of cold, heavy, salty water would be greater than when there is already a thick layer of insulating ice covering the ocean.  The length of the push is shorter but more intense.  How would this effect the whole system??

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