Climate Change and the Thermohaline Circulation

 Sea Ice, Svalbard, Norway

In my previous article on Climate Change and Carbon, I discussed the impact that carbon emissions have on climate change and global warming.  I discussed international agreements, global temperature, carbon sequestration, carbon dioxide as a sensitive indicator of climate change, and global health as a factor in how we interact with a changing world.

In this article I discuss the thermohaline circulation and its interrelationship with climate change. The thermohaline circulation may be explained by chaos theory, as a "bifurcation point", a sensitive indicator which may keep the planet under one paradigm, or place it into another paradigm, presenting planetary challenges.

Planetary cycles (Milankovitch Cycles)  indicate a trajectory at this time towards planetary cooling, or glaciation, reflecting a continuing decrease in  axial tilt (obliquity) .  This long term  cycle (41,000 years) presents psychosocial difficulties for those who are not accustomed to thinking on a scale involving geologic time. Such a scale seems way too far off to appear relevant, eclipsing by orders of magnitude scales such as 100-year floods or 500-year volcanic eruption intervals such as at Mt Rainier as discussed in my 2011 blog article.

At the same time as underlying very long term planetary cycles (e.g. obliquity) are pointing us towards planetary cooling, our earth is warming with the effects of climate change. We are in the throes of opposite systems colliding, facing very different issues.  The immediate climate change issues are important, however considering the long term factors is also relevant to the discussion.  Global health issues are tied up in both discussions, as evolution may take a variety of paths in response to planetary indicators.

My blog article, Climate Change and global health discusses some of the ramifications of health effects of climate change, including those depicted as coastal flooding.  A trend towards glaciation, a Mini-Ice Age or even in the extreme, a Snowball Earth would bring on very different changes, and adaptations and implications for global health.

The oceans are an important factor to consider in assessing such developments.  The Earth goes between icehouse and greenhouse cycles.  These cycles can be captured via examination and measurement of calcite and aragonite seas. A graph, shows the emergence of an aragonite threshold during the current period, which might indicate the emergence of a period of glaciation.  Aragonite seas  contain high magnesium calcite, and less abundantly, aragonite while calcite seas  have lower magnesium content, which increases as a threshold is reached.

The calcites  are inorganic carbonate precipitates, with calcium carbonate (CaCO3) being most common precipitate.  Other precipitates include aragonite and vaterite.  These precipitates emerge in a number of areas, including shells of marine organisms, including  plankton, foraminafera and trilobytes  (where calcite was responsible for development of eyes).
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There are a number of planetary adjustment factors that act to keep the planet in balance.  The National Oceanographic and Atmospheric Administration (NOAA) has a wide variety of information for the general public on science,  research and further  information regarding the thermohaline circulation , the ocean  and its role in climate.   The thermohaline circulation is central to the issue of planetary climate control.

Positive feedback loops work to increase the risk of global warming.  This effect occurs as the sea ice extent decreases, exposing open ocean and thus decreasing the planetary albedo.    Higher albedo is associated with higher reflectivity, or less heat retention, while lower albedo is associated with lower reflectivity and greater heat absorption.

As more heat is retained by the Earth, especially in the polar regions (the Arctic and the Antarctic), warming increases.  With increased warming comes melting, of sea ice, icebergs and glaciers, This melting may impact Arctic regions  such as Greenland and Arctic Ice, as well as the Weddell Ice Shelf in Antarctica.and Antarctic Sea Ice.  Ice may be lost from glaciers, resulting in the formation of tabular icebergs, and calving of those icebergs, which may increase melting, just as a bag of ice cubes melts faster than block ice.

The melting that occurs increases the flow of fresh water into the oceans.  This is particularly felt in the Arctic, where the thermohaline circulation travels northward from the warmer Gulf Coast of North American waters to cold North Atlantic Arctic waters.

The infusion of fresh water in the North Atlantic may disrupt the sinking of the saltier water in the North Atlantic, which develops as the result of formation of sea ice (as sea ice forms, it forms from fresh water and the surrounding water gets saltier, and sinks to deeper depths).  This infusion of fresh water in the North Atlantic could result in disruption of the thermohaline conveyor belt, thus impeding the delivery of warm water from the Gulf to northern areas in both North America and Europe, resulting in much harsher winters.  A shutdown of the thermohaline circulation could have very serious impacts on global climate.