CLICK ON THE GRAPH FOR A LARGER IMAGE.
Notice that as the luminosity increases above 50%, the growth of the treerings slows until they achieve values close to the initial response from 10% luminosity. This characteristic of bristlecone pines makes treerings growth analysis a highly inadequate proxy for assessing paleotemperatures.
So how does this physiological pathway work? By means of a primitive physiological mechanism called Photorespiration. Photorespiration occurs on bright, hot and dry days. Under those conditions, the C3 plants close their stomata for preventing loss of water. As a result, the concentration of oxygen within the air spaces of the leaves increases and the concentration of carbon dioxide decreases. This change of concentration of oxygen and carbon dioxide makes the molecule of Ribulose-1, 5-bisphosphate carboxylase oxygenase (RuBisCO) to capture oxygen to be used in the Calvin cycle instead of carbon dioxide. Consequently, the plants produce less food and slow their growth. (Odum. 2006. Pp. 48-50) (Lodish et al. 2000. Pp. 667-669)
Photosynthesis is affected in the same way on gloomy, cold and wet days. For this reason we cannot know when the slowness of plant growth was due to high or low insolation, to high or low temperature, or to high or low humidity. (Odum. 2006. Pp. 48-50)
For example, if the insolation is 210 W/m^2 on average, the growth of pines would be optimal; let us say some 140% per year, according to the diagram above these lines. If we deduced the environmental temperature anomaly from this data, we would say that that year would have been a fairly warm year, let us say 1.4 °C above the standard temperature. However, supposing that the insolation increases up to 100 %, i.e. to 420 W/m^2 on average. This would mean that the pine trees’ growth would be dramatically slowed, so the annual pines’ rings growth actually would be fairly lessened, let us say -30% a year. If we continue with the same criterion for calculating the annual temperature anomalies, this would represent an anomaly of -0.3 °C, which would be absolutely false because the insolation would have been at its peak intensity (100%) and consequently the environmental temperature would have been higher than if the pine treerings would have grown up to 140 mm a year.
The works of Michael Mann, Keith Briffa and colleagues on paleotemperatures are based absolutely on the treering growth of pines, which explains why their results always show flat temperatures for periods prior to the use of thermometers. Because of this, their graphs give false results. The latter is revealed when we compare the treerings growth from the Yamal Peninsula with the instrumental data in the last 30 years. This comparison gives a 100 % correlation which is clear indication on hard manipulation of the data to give the false impression that the pine’s treerings growth is a reliable proxy on the tropospheric temperature when in reality it is not.
On the other hand, when properly examined, the databases of other non-treering proxies always show the Medieval Warming Period.
This analysis demonstrates also that the combination of the databases from treering proxies with the databases from other proxies such as sediments, pollen, Hematite Stained Grains, etc. is always more appropriate for obtaining reliable records on variation of temperature than simply treering growth alone, which is affected by many other factors such as humidity, insolation, concentration of carbon dioxide, altitude, temperature, etc.
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