Present climatic variations

During the last hundred years the temperature of the Earth s atmosphere has varied significantly. The most important feature of this variation is the nearly steady temperature increase from the eighties of the last century until about 1945. The mean annual temperature increase was 0.008 C. From 1945 the temperature 

Changes in temperature of surface air compared to the value observed in 1880 according to Mitchell (see SMIC, 1971). (By courtesy of Massachusetts Institute of Technology) 

Variation of temperature (/. I and solar radiation intensity (J according to Budyko (1969). / annual mean 2 ten year mean. (By courtesy of Tellus) 

Budyko (1969) argues that the study of present climatic variations is particularly important since the thermal state of the Earth-atmosphere system as well as the present ice cover are in unstable equilibrium (during 90 % of the Earth s history from the beginning of the Paleozoic era our planet was free of ice, see Section 6.1). A relatively small change in temperature would lead to irreversible change (positive feedback, see previous section). 

During the last hundred years the parameters characterizing the circulation also underwent significant fluctuations. Lamb demonstrated (see SMIC, 1971) that the number of days with westerly winds over the British islands increased until the middle of twenties while it decreased until about 1960. Lamb speculated but did not prove that these variations in the circulation pattern are connected with changes in temperature and precipitation fields. 

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Among these causes only those mentioned in point 3 are within the scope of this book. We shall discuss them in some detail in Section 6.5 in connection with present climatic variations. Of the other factors we shall clarify here only point 6, which is probably less known than the others. If in our climatic model (see later) the random modification of initial conditions results in a nonzero probability that the climate remains unchanged, then the climate is called stable. If the system has only one single stable climate (and possibly many unstable ones) it is said to be transitive (see more detail in SMIC, 1971). Otherwise, i is said to be intransitive. According to Lorenz (1968) the climate of the Earth is intransitive. This means that climate can go from one stable state to another without the modification of external or initial conditions, that is, variations are due to the internal fluctuations of the system. 

If the stable isotope ratio of 13C/12C is to be further measured in tree rings and interpreted as an indicator of climate variation, (and we have barely begun to initiate its use as a thermometer in the present work, confining our measurements to the stable isotopes in water, because water is so abundant compared to carbon dioxide and because the dependence of its isotope ratios is relatively simple compared with those of carbon dioxide), some more sophisticated considerations must be given to the distribution of carbon dioxide among the reservoirs on the surface of the earth. 

Instead one must still grope towards qualitative, spatial coincidences. The forest and tundra biomes of Canada coincide fairly well with certain climatic distributions. The southern limit of the boreal coniferous forest is close to a specific isoline of net radiant energy input from Alaska to Newfoundland. The arctic treeline is close to a specific isotherm for mean daily July temperature. These climatic isolines will be shifted northwards by 150 to 400 km at equilibrium with doubled CO2. Will the vegetation follow them There is scattered evidence that the dryer, warmer conditions of early mid-Holocene times did indeed see northward shifts of individual species, and that temperatures were then about as much above present levels as one would infer from the vegetational shifts. Closer than this one cannot go. The science of linking climatic variation to ecosystem structure, function and dynamics is still in a primitive state. 

We have to emphasize that the correct prediction of the future COz concentrations is one of most important tasks of atmospheric science at present. This is explained by the fact that the C02 content of our atmosphere regulates, among other things, the radiation balance of the Earth-atmosphere system by absorbing infrared radiation emitted by the surface. Thus, we cannot exclude the possibility that the increase of the carbon dioxide concentration may cause inadvertent climatic variations in the future (see Chapter 6). 

After this discussion the reader is surely curious to know wich factor is the most important in the control of climatic variations. Unfortunately the experts are not able to make such a choice at present. Furthermore, it cannot be excluded that the interaction of several factors produced past climatic variations. 

The opium alkaloid content of P. somniferum varieties cultivated in Bulgaria and in Hokkaidohas been determined. The effects of planting density on yield of alkaloids and of climatic variations on the accumulation of morphine in this species have been noted.A Swedish variety has been bred to produce a low morphine content. The alkaloids present in the stamens of P. somniferum at different stages of their development have been examined. Evidence has been produced that the alkaloids are produced, stored, and translocated in the vacuolar sap of the vesicles present in the latex of P. somniferumThe thebaine content of P. bracteatum at various times in the growing season and a g.l.c. method of... 

The data presented in Table 1 clearly show that the weights of uteri and ovaries and number of ovarian follicles (sum of ovarian follicle types 6, 7,8 and atretic) in bank vole females were lower when the females maturated in the presence of other females. Bank voles reared in the enclosure and outdoor cages were under the influence of the same climatic variations and fed with the same diet, so social cues are suspected as the main factors affecting gonadal activity of these females. 

Barron, E.J., Solan, J.L. and Harrison, C.G.A. (1980) Potential significance of land-sea distribution and surface albedo variations as a climatic forcing factor 180 m.y. to the present. Paleoneogr. Paleoclimatol. PaleoecoL, 30, 17- 0. 

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