GLOBAL WARMING

     In its most basic form global warming occurs when the energy entering the atmosphere and incident upon the ocean and earth’s surface is greater that the energy radiating back out to space. The rate of outward radiation depends upon the concentration of various gases in the atmosphere. There is clear evidence that there has been an increase in the concentration of several gases in the atmosphere which slow down the outward flow of energy to space. The gas of primary interest with respect to human energy use is carbon dioxide (CO₂) — the principal end product of burning fossil fuels. Data from the top of Moana Loa on the island of Hawaii shows that CO₂ in the atmosphere has increased from a background value of 280 parts per million (ppm) to 370 ppm and climbing.

     This increase is coincident with the increase in fossil fuel use since the start of the Industrial Revolution. In fact, an accounting of the amount of CO₂ that "should" be in the atmosphere from fossil fuel use comes up short. This problem of the "missing carbon" has puzzled global modelers for decades and has resulted in numerous articles speculating various land based carbon sinks. It is most likely, however, that the "missing carbon" is in the ocean. Modelers have been using gas exchange rates determined from experiments using fresh water (rather than seawater). Measurements conducted at the University of Hawaii in the late eighties and early nineties showed that the gas exchange rates of seawater are significantly more rapid than that of fresh water. Part of the explanation for this is that molecular diffusion of gases in seawater is faster than in fresh water due to structural differences between the two similar liquids created by the introduction of the salt present in seawater. This was determined through research conducted by Dr. Stephen Oney of OCEES International, Inc. while he was working at the University of Hawaii. Other research conducted at the University of Hawaii by Drs. Hans Krock (also of OCEES), Stephen Oney and Manfred Zapka showed that the macro-scale characteristics of seawater gas exchange were important in determining the rate at which the atmosphere exchanges gases with the ocean as well. This work resulted in two U.S. patents important to Open-Cycle OTEC (OC-OTEC), OTEC fresh water production as well as to the global warming question.

     If the "missing carbon" is indeed in the surface layer of the ocean then there are chemical and biological consequences — especially in the tropical zone. Much of the tropical ocean is low in productivity because of nutrient limitations, usually nitrogen and/or phosphorus. Because it is not limiting, additions of CO₂ would not enhance productivity but would lower the pH slightly. This lower pH may be a factor in the coral damage that has been observed in a number of reefs around the world. This damage has been attributed to a rise in seawater temperature or to bacterial contamination of human origin. While these may be factors in certain locations and in certain types of coral, the lowering of pH should also be considered since we know that coral have an optimum pH range and are especially sensitive to a low pH.

A representation of the Hydrologic Cycle.

     The ocean is the primary temperature regulator of the surface of the planet. Seawater has a much greater heat capacity than does air (or the land surface for that matter). The tropical ocean surface layer is the primary storage area for solar energy on earth. From there it is redistributed to higher latitudes by wind, the hydrologic cycle (evaporation/rain) and ocean currents. The greater amount of heat energy in the ocean and its redistribution to higher latitudes has resulted in a rise in sea level. This is due not only to ice melting but also due to thermal expansion of the seawater (about 50 — 50) caused by this additional thermal storage. The rise in sea level is especially important for atolls and low lying continental coastal areas.

     The amount of extra heat energy stored in the upper layer of the ocean during this recent period of global warming is very large in comparison to human energy usage. For example, it would take several hundred years of human energy use to equal the extra energy that has been stored in the ocean surface layer over the last forty years.

     Another effect of global warming is a change in the regional climates of the earth due to changes in wind patterns. Some areas become dryer while others experience flooding. There are also changes in the distribution of diseases and ranges of ecosystem types and crop growing seasons. Some of these changes might be considered beneficial but most appear to be detrimental. In any case, with increased fossil fuel use these changes will become more pronounced and disruptive of existing land use patterns.

     While fossil fuel use adds to the problems associated with global warming, OTEC systems take advantage of the additional thermal energy stored in the upper layer of the tropical ocean. It should also be noted that even large scale human use of the ocean energy resource through OTEC implementation is miniscule (less than 0.1%) in comparison to the natural energy flux. This is within the noise of the natural system in that it is smaller than its annual fluctuation. In any case, OTEC simply substitutes "useful work" for "random work" and does not change the overall global energy flux. The net positive change is that large-scale deployment of OTEC systems can contribute greatly to eliminate the emissions of CO₂, CO, particulate carbon, NO_x, and SO_x and thereby not only reduce global warming but greatly reduce smog and acid rain as well.