The greenhouse effect

This rise in atmospheric CO2 levels is of increasing concern because of a phenomenon that has come to be known as the 'greenhouse effect' (Gribbin, 1988b). Energy reaches the earth's surface as short-wavelength radiation in sunlight and leaves again as long-wavelength IR (infra-red) radiation. The escape of IR radiation is slowed by the presence in the atmosphere of CO2, methane and other rare gases whilst incoming radiation is unaffected. Without these gases, the earth would have an average temperature around about freezing point. However, too great a concentration of these gases delays the escape of IR radiation and allows the earth to warm up. The increase in concentration of CO2 over the past century and a half appears to be having just that effect. The average global temperature has risen by about 0.5°C during the present century. However, it is not absolutely certain that this rise has been caused by the greenhouse effect. What climate researchers are certain of is that if we continue to add CO2 to the atmosphere at the present rate, then global temperatures will rise, perhaps as much as 1.5-4.5°C in the next 50 to 100 years. This prospect is now being taken very seriously by governments and target levels for the reduction of CO2 emissions have been set.

As we have seen above, the absorption of CO2 by the oceans plays a vital role in mitigating the greenhouse effect. However, if the temperature of the oceans increases due to global warming, this will reduce the solubility of CO2 and might consequently lead to a net release of CO2 from ocean to atmosphere thus compounding the problem. Obviously the relationships of these processes with respect to climatic effects are complex and not yet well understood. They are now under intensive study by meteorologists and marine scientists. A recent review by Smith and Hollibaugh (1993) has shown that the role played by coastal ecosystems in the global carbon budget is even more important than had previously been thought.

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