"Do you know what CO2 levels
by duckman - 7/22/07 5:44 PM
In reply to: Re: facts. by Kees Bakker Moderator
were before industrialized mankind? Were they higher or lower?"
lower and higher is the most complete answer. what is different is that we are now living in a post industrial age that creates man made co2 emissions. that we have control of; not a pre-human landscape.
" During the Ordovician, Southern Europe, Africa, South America, Antarctica and Australia remained joined together into the supercontinent of Gondwanaland, which had moved down to the South Pole. North America straddled the equator, and was about 45 degrees clockwise from its present orientation. Western and Central Europe were separate from the rest of Eurasia, and were rotated about 90 degrees counterclockwise from their present orientation, and was in the southern tropics. North America is engaged in a slow collision with the microcontinent of Baltica, which forms the core of what is later to become Europe. The Iapetus Ocean continues to shrink as the previously passive margins of Baltica and North America converge. Where the Iapetus was, mountains are thrust up, remnant strata of which remain today in Greenland, Norway, Scotland, Ireland and north-eastern North America. Scotland and England are united into a single landmass.
As a natural consequence, a good deal of attention has been focused on the causes of the Ordovician Ice Age. In fact, it is not easy to see how an ice age could have occurred. Atmospheric carbon dioxide levels are believed to have been 8 to 20 times their current values. This ought to have prevented anything approaching an ice age. Sea levels were high through most of the Ordovician. They dropped, dramatically (about 50 m), in connection with the ice age, but it is hard to tell whether this was cause, effect, or both. One independent factor which would affect both pCO2 and sea level is the rate of sea floor spreading along mid-ocean ridges. As we might expect, the length of well-established mid-ocean ridges, i.e., the ridge between Gondwana, to the south, and Baltica plus Laurentia, to the north, was unusually short during the Late Ordovician. A former ridge between the two northern continents became inactive about this time. However, there may have been a very long ridge to the Northwest of Laurentia. The information is too sparse to be certain. In any event, the absence of active ocean crust formation would only affect the rate of CO2 outgassing, not the rate at which it was locked away in sediments.
The state of the art in mathematical modeling of the problem is described in the recent work of Hermann et al. (2004). The results are frustratingly uninformative. Sea surface temperatures for the later Ordovician are extremely sensitive to atmospheric carbon dioxide levels and to not much else. Even the changes in geography, which brought more land surface close to the South Pole, seem to have little effect on the outcome. The result in the image indeed predicts glaciers in Gondwana at the end of the Late Ordovician. Unfortunately, it also predicts glaciers in Gondwana at the beginning of the Late Ordovician, even with much higher sea levels. Thus, if the models have anything to tell us, it is that there must have been a very strong draw-down of CO2 over the Late Ordovician. No one, at this point, has been able to offer evidence suggesting a plausible agent which would remove roughly half of all atmospheric carbon dioxide in 10-15 My."