Global warming...
Out of context: Reply #611
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- mpfree0
you asked for one academic reference. one right?
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Mid-Cretaceous pCO2 based on stomata of the extinct conifer Pseudofrenelopsis (Cheirolepidiaceae)
Matthew Haworth, University of Oxford, Earth Science, Oxford, Oxfordshire OX1 3PR, UK; et al. Pages 749-752.Atmospheric carbon dioxide (CO2) is a major factor that determines global climate, and in order to predict future climate change it is important to understand the role CO2 levels have played in climate systems in the past. One method for reconstructing CO2 concentration involves the relationship between the number of stomata on a leaf and the atmospheric CO2 concentration in which the plant grew. Stomata are the tiny pores through which plants take up CO2, but also lose water at the same time. This means that plants have to balance CO2 uptake against water loss, and can respond to variations in CO2 levels by altering the number of stomata. During periods of high atmospheric CO2, plants can have lower numbers of stomata, and so lose less water while maintaining the same rate of CO2 uptake. This inverse relationship between the number of stomata and atmospheric CO2 allows estimation of the ancient atmospheric CO2 concentration from the density of stomata on fossil leaves. Using the fossil conifer Pseudofrenelopsis, Haworth et al. have reconstructed CO2 levels for the mid-Cretaceous period. The Cretaceous is known to have been a time of relative global warmth, with high levels of atmospheric CO2 responsible for this global greenhouse climate. Their results suggest, however, that atmospheric CO2 levels were lower than previously thought and relatively stable throughout the mid-Cretaceous, rather than dramatically fluctuating, as has been suggested in other reconstructions. Mid-Cretaceous CO2 levels were still significantly higher (2 to 3 times) than current concentration.
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Maybe we will go beyond the level of the Cretaceous, however with that being said who's to say we can't co-exist at those levels. Life, "endothermic mammals", at that point did for how many millions of years!?
According to scientists, the Cretaceous period lasted from 144 to 65 Million. That's 79 Million years long. About average for a Period. We're about 1/65th of that length as humans.