There has been a vast amount of energy devoted to developing climate change models. These appear to have been largely focused on dividing the surface of the globe into ever smaller increments and summing the effect of higher carbon dioxide concentration in the atmosphere on groupings of such increments to provide regional predictions of climate change effects. This emphasis on the atmosphere fails to account adequately for many other physical, chemical and biological processes that are or may be involved. These notes attempt to redress the balance by hypothesizing on the possible involvement of these other factors. More specifically, this analysis is based particularly on Ice Age dynamics and the lessons we can learn relevant to present-day climate. While to most people the Ice Age is impossibly remote and seemingly divorced from current realities, it is possible that the processes set in place between 100,000 and 15,000 years ago are still dominating our environment. More specifically, it is suggested that the terrestrial system has two dramatically different modes of operation, and under appropriate conditions can switch abruptly from one to the other in the course of one or two decades, which might be soon upon us. This possibility makes it important to understand the drivers behind these two modes of operation simply described as the ‘cooling’ and ‘warming’ modes.
The ‘Cooling’ Mode
Ocean Circulation
The important influence that the oceans have on the climate of our ‘water planet’ are recognized in references to La Nina and El Nino and even more importantly to the Gulf Stream in moderating the climate of Europe. Further, it is recognized that the flow of the Gulf Stream toward the Arctic results from the sinking of large volumes of cold, salt-dense water off Greenland to the ocean floor driving the global ‘thermohaline’ system, commonly referred to as the ‘Great Ocean Conveyor’. It is further recognized that dilution of the Arctic Ocean by melting Arctic ice lowers the surface water density to the point that it no longer sinks. Under these conditions the Gulf Stream will slow and eventually stop in the Arctic, taking a more southerly course around the Sargasso Sea in the mid-Atlantic. The consequence of this change of flow is that temperatures in Europe will cool by 10*C to 15*C, and ice caps will reform and gradually spread during the succeeding 100,000 years.
The important influence that the oceans have on the climate of our ‘water planet’ are recognized in references to La Nina and El Nino and even more importantly to the Gulf Stream in moderating the climate of Europe. Further, it is recognized that the flow of the Gulf Stream toward the Arctic results from the sinking of large volumes of cold, salt-dense water off Greenland to the ocean floor driving the global ‘thermohaline’ system, commonly referred to as the ‘Great Ocean Conveyor’. It is further recognized that dilution of the Arctic Ocean by melting Arctic ice lowers the surface water density to the point that it no longer sinks. Under these conditions the Gulf Stream will slow and eventually stop in the Arctic, taking a more southerly course around the Sargasso Sea in the mid-Atlantic. The consequence of this change of flow is that temperatures in Europe will cool by 10*C to 15*C, and ice caps will reform and gradually spread during the succeeding 100,000 years.
Next Ice Age
Vulnerability
Recent sampling of the North Sea indicates salinity is decreasing, and observations of Arctic Ice and Greenland glacier melting suggest we may be approaching the conditions that will slow and eventually halt the Great Ocean Conveyor, thereby forcing the Gulf Stream into a more southerly path.
Recent sampling of the North Sea indicates salinity is decreasing, and observations of Arctic Ice and Greenland glacier melting suggest we may be approaching the conditions that will slow and eventually halt the Great Ocean Conveyor, thereby forcing the Gulf Stream into a more southerly path.
No Circulation – surface consequences
The solubility of carbon dioxide in cold sea water is much higher than in warm tropic surface water, and the water sinking off Greenland carries large quantities of atmospheric CO2 into the ocean depths where it is sequestered for centuries, ultimately for millenia. The CO2 concentration in the atmosphere would therefore be expected to rise when the conveyor is slowing. Further, the reduced volume of water sinking off Greenland implies a corresponding
decrease in deep water rising in the Pacific circulation. This deprives the surface waters of a supply of nutrients from the ocean floor, notably iron, and a corresponding reduction in surface phytoplankton activity and carbon sequestered in the resulting organic detritus.
The solubility of carbon dioxide in cold sea water is much higher than in warm tropic surface water, and the water sinking off Greenland carries large quantities of atmospheric CO2 into the ocean depths where it is sequestered for centuries, ultimately for millenia. The CO2 concentration in the atmosphere would therefore be expected to rise when the conveyor is slowing. Further, the reduced volume of water sinking off Greenland implies a corresponding
decrease in deep water rising in the Pacific circulation. This deprives the surface waters of a supply of nutrients from the ocean floor, notably iron, and a corresponding reduction in surface phytoplankton activity and carbon sequestered in the resulting organic detritus.
No Circulation – deep consequences
Study of Antarctic Ice cores has shown that once this cooling trend in Europe is established, it continues to deepen for 100,000 years, with the Earth’s surface becoming progressively colder, drier, windier and the atmosphere dustier. During this time, in the absence of deep ocean water circulation, the carbon dioxide concentration of the deep water increases as a result of bacterial decomposition of the organic material settling from the surface. Dissolved oxygen is depleted; atmospheric dust also settles into the depths where, in the absence of oxygen, iron on the dust surface dissolves as ferrous chloride and soluble bulk nutrients such as nitrogen and phosphorous also accumulate.
Study of Antarctic Ice cores has shown that once this cooling trend in Europe is established, it continues to deepen for 100,000 years, with the Earth’s surface becoming progressively colder, drier, windier and the atmosphere dustier. During this time, in the absence of deep ocean water circulation, the carbon dioxide concentration of the deep water increases as a result of bacterial decomposition of the organic material settling from the surface. Dissolved oxygen is depleted; atmospheric dust also settles into the depths where, in the absence of oxygen, iron on the dust surface dissolves as ferrous chloride and soluble bulk nutrients such as nitrogen and phosphorous also accumulate.
Salt Build-up
During this 100,000 year cooling cycle water evaporates from the warm, equatorial oceans and accumulates as ice at the poles and, as a consequence, the ocean level drops 120 metres and the salinity of the ocean surface gradually increases.
During this 100,000 year cooling cycle water evaporates from the warm, equatorial oceans and accumulates as ice at the poles and, as a consequence, the ocean level drops 120 metres and the salinity of the ocean surface gradually increases.
The
‘Warming’ Model
Flipping the Switch Eventually, the salinity of the
Arctic Ocean rises again to a level at which the density of the surface water
exceeds that of the deep water and starts sinking, thereby restarting the Great
Ocean Conveyor. A corresponding flow of deep water in the tropical Pacific rises
to the surface carrying with it the carbon dioxide, ferrous chloride and
nutrients accumulated over the 100,000 years of the Ice Age. This up-flow
permits release to the atmosphere of the vast quantity of carbon dioxide
sequestered at depth, while providing the iron and nutrients to support a
tremendous phytoplankton bloom. The bacterial decomposition of this algal matter
on the ocean surface generates large amounts of volatile dimethyl sulphide that
seed low level cloud formation, which, coupled with rising atmospheric CO2
concentrations, slows the loss of infra red energy from the Earth’s surface.
This leads to progressive warming of the ocean surface, more evaporation and
cloud formation, all facilitating a rapid demise of the Ice Age.
Conclusions
Sea level data suggest that at the end of the last Ice Age this abrupt
transition into the ‘Warming’ mode, started 15,000 years ago and was essentially
completed 7,000 years ago. Since then, the sea level and temperature have been
in a state of dynamic equilibrium with only relatively minor fluctuations. The
recent increase in atmospheric CO2 concentrations may be a reflection of the
progressive failure of the Ocean Conveyor, reducing the volume of upwelling
nutrient laden deep water to the ocean surface and in turn the capacity of the
ocean phytoplankton sink for CO2. Short-term global warming, by stimulating
melting of Arctic ice to further dilute the surface waters of the Arctic Ocean,
may presage another abrupt change in Earth’s operating mode to a long-term
cooling cycle and the next Ice Age.
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