Why we don't have to worry about about CO2.
Carbon dioxide is essential for plants. In fact, it is essentially for almost all life. With no carbon dioxide in the atmosphere, there would be no photosynthesis, no plants, no animals feeding on plants, and no animals feeding on other animals. The only kind of life would be microbes like bacteria. We should be delighted that there is carbon dioxide in the atmosphere, because without it we would not exist either.
The climate alarmists/catastrophists are claiming that CO2 have a large impact on climate and that we should worry. They are wrong. Carbon dioxide have a very small impact on climate. The positive impacts of its increase the past 150 years, and its possible increase the coming few hundred years, far outweighs its negative impacts. To this we may add that the climate catastrophists overestimate future levels of carbon dioxide in the atmosphere. This they do both because they overestimate how much the humans will emit in the future, and because they underestimate how fast nature can remove the extra CO2 from the atmosphere.
One argument which the alarmists use to back their claims, is that data from boreholes in the Antarctic ice show that temperature and CO2 correlate very well. What they don't tell the public, however, is that correlation does not prove causation. And, in fact, the cause is precisely the opposite of what the alarmist would like you to belive. In the past couple of years, new and better analysis of the Antarctic ice data, giving a better time resolution, have shown that first temperature rises, and then carbon dioxide levels increase. It is the temperature increase which causes the increase in carbon dioxide and not the other way around. The extra CO2 could at most add a little extra warming to what is going on, but not even that is certain.
The main reason why CO2 can only have a small impact on the climate of the world is called saturation. This is a phenomena well known from theory and observations of spectral lines in stellar atmospheres. The same laws of physics hold for the atmosphere of the Earth, although the pressure, density and temperature of course could be very different. An atom or a molecule does not absorb light and other electromagnetic radiation at all wavelengths. It only absorbs in narrow regions in the electromagnetic spectrum. These narrow regions are called spectral lines, or if they are sufficiently broad, spectral bands. Every atom or molecule has its own characteristic sequence of spectral lines.
It is very typical in a stellar atmosphere, that when the number of atoms or molecules of a particular species is small, the amount of radiation absorbed in any spectral line increases with the number of absorbing particles (that is, atoms or molecules). When the number of absorbing particles increases even further, however, they will start to screen each-other. This means that particles will receive less radiation than expected, because other particles have already absorbed the radiation heading their way. The radiation will eventually be re-radiated, but then usually at another wavelength, where the atom or molecule cannot absorb it. This screening also means that the total absorption of radiation no longer will increase as fast as the number of particles. It is in fact possible that the total absorption remains almost constant in spite of an increase in the number of absorbing particles. This phenomena is called saturation, because the absorption in the spectral line becomes saturated and no longer reacts to the number of particles occuring in the path of the light.
Carbon dioxide in the Earth's atmosphere has exactly one important spectral line in the infrared part of the spectrum. This line is clearly saturated. If you increase the number of CO2 molecules in the atmosphere, not much will happen. The amount of infrared radiation, that is, heat, that will be absorbed changes only by a minimal and insignificant amount. Only if we increase the amount of carbon dioxide in the atmosphere by orders of magnitude, will there be a noticeable change. This, on the other hand, will not happen, both because the human emission will never be large enough and because there are green plants.
Photosynthesis is a process by which green plants turn carbon dioxide and water into sugar, which in turn could be used to build up organic material. Its by-product is oxygen, which was a dangerous poison to the life of that era when it first started to appear in the atmosphere a few billion years ago, but now is essential to animals. Plants growing on land get their water from the ground, through the roots. They take up carbon dioxide through small holes, called stomata, in their leaves and stems. When the stomata are open, to let CO2 in, water may escape from the plant. The more CO2 there is in the atmosphere, the less time does the plant need to have its stomata open to get enough carbon dioxide, and thus the less water it will lose. The more CO2 there is in the atmosphere, the more organic material may also be produced by the plant in any given time, of course, provided it also has enough of essential nutrients. Thus an increase in the concentration of CO2 in the atmosphere has the two-fold advantage of allowing plants to grow faster and allowing them to use their water more efficiently. It is not surprising that several investigations have shown that the world has become greener in the past few decades. There have been more and larger plants, and especially so in arid and semi-arid areas. The climate alarmists have tried to "blame" the greening of the planet on global warming. They have problems trying to do this. First of all: How could greening of the planet be a bad thing? On the contrary, it is a good thing. Animals, including humans, get more food when any given area of land can support more and bigger plants. Second: How could global warming cause greening of deserts? It cannot, of course. Undoubtedly, the greening of the Earth is mainly caused by the increasing amount of CO2 in the atmosphere. Local, not global, warming could contribute a little in some areas, but on the average, for the entire globe, its significance is unimportant.
So there is no need to worry about the increasing amount of carbon dioxide in the atmosphere. The climate alarmists are wrong.
About cause and correlation of CO2 and temperature:
Indermuhle, A., Monnin, E., Stauffer, B. and Stocker, T.F. 2000. Atmospheric CO2 concentration from 60 to 20 kyr BP from the Taylor Dome ice core, Antarctica. Geophysical Research Letters 27: 735-738.
Monnin, E., Indermühle, A., Dällenbach, A., Flückiger, J, Stauffer, B., Stocker, T.F., Raynaud, D. and Barnola, J.-M. 2001. Atmospheric CO2 concentrations over the last glacial termination. Nature 291: 112-114.
Mudelsee, M. 2001. The phase relations among atmospheric CO2 content, temperature and global ice volume over the past 420 ka. Quaternary Science Reviews 20: 583-589.
About the greening of the Earth:
Ahlbeck, J.R. 2002. Comment on "Variations in northern vegetation activity inferred from satellite data of vegetation index during 1981-1999" by L. Zhou et al. Journal of Geophysical Research 107: 10.1029/2001389.
Bert, D., Leavitt, S.W., Dupouey, J.-L. 1997. Variations in wood ð13C and water-use efficiency of Abies alba during the last century. Ecology 78: 1588-1595.
Eamus, D. 1996. Responses of field grown trees to CO2 enrichment. Commonwealth Forestry Review 75: 39-47.
Eklundh, L. and Olssson, L. 2003. Vegetation index trends for the African Sahel 1982-1999. Geophysical Research Letters 30: 10.1029/2002GL016772.
Feng, X. 1999. Trends in intrinsic water-use efficiency of natural trees for the past 100-200 years: A response to atmospheric CO2 concentration. Geochimica et Cosmochimica Acta 63: 1891-1903.
Grunzweig, J.M., Lin, T., Rotenberg, E., Schwartz, A. and Yakir, D. 2003. Carbon sequestration in arid-land forest. Global Change Biology 9: 791-799.
Hemming, D.L. 1998. Stable Isotopes in Tree Rings: Biosensors of Climate and Atmospheric Carbon-Dioxide Variations. Ph.D. Dissertation. University of Cambridge, Cambridge, UK, 270 p.
Idso, S.B. and Kimball, B.A. 2001. CO2 enrichment of sour orange trees: 13 years and counting. Environmental and Experimental Botany 46: 147-153.
Idso, S.B., Kimball, B.A., Akin, D.E. and Kridler, J. 1993. A general relationship between CO2-induced reductions in stomatal conductance and concomitant increases in foliage temperature. Environmental and Experimental Botany 33: 443-446.
Kaufmann, R.K., Zhou, L., Tucker, C.J., Slayback, D., Shabanov, N.V. and Myneni, R.B. 2002. Reply to Comment on "Variations in northern vegetation activity inferred from satellite data of vegetation index during 1981-1999: by J.R. Ahlbeck. Journal of Geophysical Research 107: 10.1029/1001JD001516.
Leavitt, S.W., Idso, S.B., Kimball, B.A., Burns, J.M., Sinha, A. and Stott, L. 2003. The effect of long-term atmospheric CO2 enrichment on the intrinsic water-use efficiency of sour orange trees. Chemosphere 50: 217-222.
Saxe, H., Ellsworth, D.S. and Heath, J. 1998. Tree and forest functioning in an enriched CO2 atmosphere. New Phytologist 139: 395-436.
Zhou, L., Tucker, C.J., Kaufmann, R.K., Slayback, D., Shabanov, N.V. and Myneni, R.B. 2001. Variations in northern vegetation activity inferred from satellite data of vegetation index during 1981-1999. Journal of Geophysical Research 106: 20,069-20,083.
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