This is the fourth of the series Global Warming - Tale of the Tiger.Read the first posting in this series: Tale and a description of the figure to the left. I believe the apparent 0.8ºC increase in Global Temperature over the past 150 years is due to three major causes and one minor one, as indicated by the parts of the "tiger". (The second posting details Data Bias and the third Natural Cycles.)
OCEAN CARBON
This posting is about OCEAN CARBON that I estimate is responsible for about 20% of the apparent warming of the surface of the Earth over the past 150 years.
COMPONENTS OF ATMOSPHERIC CARBON GASSES
Atmospheric carbon gasses may be subdivided into three categories: 1) Historically normal levels, typical for the past 100,000 years or so, 2) excess carbon gasses over historically normal levels due to non-human causes, mainly the general warming of the surface of the Earth over the past 150 years, and 3) excess carbon gasses due to human activities, primarily the burning of previously sequestered carbon (coal, oil, natural gas). Although there are many carbon gasses, the following analysis centers on CO2, which is the main one.
1) What are the historically normal levels? Homo sapiens, hominids with large brains about the size of ours, have been on Earth for about 100,000 years. Humans capable of understanding and speaking metaphoric languages have been around for about 10,000 years. Industrial humans capable of having a substantial effect on atmospheric carbon have been around for only about 200 years. During the period from 100,000 to 200 years ago, according to ice core data, atmospheric CO2 gas has varied from about 180 to 280 parts per million (ppm). Thus, anything over 280 ppm is historically excessive.
2) What are the non-human-caused excess carbon levels? Current CO2 levels are about 390 ppm, which is 110 ppm in excess of the historical maximum. Of that, I believe around 70 to 80 ppm is due to the transfer of carbon from the surface of the Earth to the atmosphere, as a result of the actual global warming of about 0.5ºC over the past 150 years. I call this "ocean carbon" because most of it has fizzed out of the oceans over the past century and a half. The posting you are currently reading has to do with "ocean carbon".
3) What are the human-caused excess carbon levels? The remaining 30-40 ppm of excess CO2 in the atmosphere is due to human burning of previously sequestered carbon. The next posting in this series will detail what I call "human carbon".
THE "GREENHOUSE" EFFECT
When we were kids, we learned about the "greenhouse" effect. Visible light from the sun passes through the glass roof of the greenhouse. As this light energy floods in and illuminates the plants, soil and rocks, they heat up and emit infrared radiation. Since the infrared radiation is of a longer wavelength, it cannot pass back out through the glass, which is why (we were taught) the greenhouse heats up. Well, what we learned was true, but it turns out that the sun's heat stays within the greenhouse mostly because the side walls prevent the hot air from escaping. Nowadays you can build a good greenhouse with plastic materials that pass both visible and infrared radiation. As long as you make the building airtight it will work. On the other hand, a glass-roofed greenhouse that is not airtight will not work well.
WARMING DUE TO "GREENHOUSE GASSES"
CO2 in the atmosphere acts something like the glass roof of a greenhouse. Visible light passes through it fairly freely, but infrared radiation does not. Thus, as the level of CO2 in the atmosphere has increased from the historical maximum of about 280 ppm to the current level of about 390 ppm, more infrared radiation has been trapped in the atmosphere and the Earth has warmed considerably as a result.
I believe global warming is responsible for an actual increase of about 0.5ºC. Of that amount, about 0.1ºC to 0.2ºC is due to positive feedback from carbon gasses in the atmosphere that are in excess of historical levels and not due to human activities. This increase, which is about 20% of the apparent increase of 0.8ºC, is not under human control.
The fact that rising CO2 triggers positive feedback has led some to worry we may come to a "tipping point" where the CO2 increase triggers a temperature increase that triggers further CO2 increases and it all goes out of control. No need to worry. There is evidence that the current levels of CO2 are blocking nearly all the infrared radiation, so additional CO2 has little effect. Even doubling current levels will not cause a large increase in global warming. Beyond a certain point, if you double or triple the thickness of glass in the roof of a greenhouse, it will have little positive effect. (Consider a sun-blocking curtain on a window. If one curtain blocks, say, 90% of the sunlight, adding a second curtain will only block an additional 9%, and a third curtain less than 1% - the "Law of Dimimishing Returns".)
WHY DOES CO2 COME OUT OF THE OCEANS AS THEY WARM?
You are all familiar with the way a cold can of soda warms up and loses its "fizz" when left open on a hot day. The CO2 comes out of solution and goes into the atmosphere. That CO2 got absorbed into the soda at the factory when the cold liquid was exposed to concentrations of CO2 at high pressures.
The rate and direction of transfer of CO2 between the atmosphere and the oceans depends on many factors, mainly the concentration of CO2 in the air and water and the temperatures of the air and water. At current levels of CO2, the cold polar waters are net absorbers of CO2 from the atmosphere and the warm equatorial waters are net emitters of CO2 into the atmosphere. The temperate waters in-between either absorb or emit CO2 according to daily and seasonal temperatures.
As the Earth has warmed over the past 150 years, the colder waters have warmed a bit and therefore currently absorb a bit less carbon gasses than they did in the past. At the same time, the equatorial waters have also warmed and therefore emit a bit more carbon than in the past. The temporal waters also warmed and they absorb a bit less and emit a bit more. The result has been a net increase in atmospheric carbon of about 70-80 ppm over the past 150 years.
WHY ARE NORMAL LEVELS OF CO2 ESSENTIAL FOR LIFE ON EARTH?
Absent normal levels of CO2 in the atmosphere, the Earth would be a very cold place, unable to support life. Atmospheric CO2 is necessary for the growth of plants which obtain most of their mass from absorbtion of atmospheric carbon, creating carbohydrates and releasing oxygen into the atmosphere. Animals breathe the oxygenated air and feed on plants and digest the carbohydrates, releasing carbon dioxide and methane back into the atmosphere, where it is ingested again by the plants and so on in the carbon cycle of life.
Modest increases in atmospheric CO2 are beneficial to most plants as are moderate increases in temperature. There is NO short-term problem. However, as a conservative, I have a bias against relatively rapid change into unknown or unproven scenarios. Quite apart from global warming, I am sufficiently concerned about rapidly rising CO2 levels that I favor reasonable, concerted worldwide action, see Carbon Tax YES!, Cap and Trade NO!
CONCLUSIONS
Global warming, mostly due to natural cycles, has raised the temperature of the Earth causing the surface (mainly the oceans) to become a net emitters of CO2, responsible for about 70 - 80 ppm of the excesss atmospheric CO2 over historical levels. This naturally-caused temperature increase and resultant CO2 increase has increased the "greenhouse effect" and is responsible for about 20% of the apparent global warming we have experienced over the past 150 years. However, we are not near any "tipping point" as some of the alarmists claim.
Ira Glickstein
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