wanton dwarf
Member
"Plimer's stated value of 4000 ppmv or greater is taken from Robert Berner's GEOCARB, a well-known geochemical model of ancient CO2. As the Ordovician was so long ago, there are huge uncertainties for that time period (according to the model, CO2 was between an incredible 2400 and 9000 ppmv.) Crucially, GEOCARB has a 10 million year timestep, leading Berner to explicitly advise against using his model to estimate Late Ordovician CO2 levels due its inability to account for short-term CO2 fluctuations. He noted that "exact values of CO2... should not be taken literally."
What about evidence for any of these short-term CO2 fluctuations? Recent research has uncovered evidence for lower ocean temperatures during the Ordovician than previously thought, creating ideal conditions for a huge spurt in marine biodiversity and correspondingly large drawdown of CO2 from the atmosphere through carbon burial in the ocean. A period of mountain-building was also underway (the so-called Taconic orogeny) increasing the amount of rock weathering taking place and subsequently lowering CO2 levels even further. The evidence is definitely there for a short-term disruption of the carbon cycle."
10 million years is not a short term fluctuation.
Ocean temperatures will be the average for the planet for the period of life, it will not fluctuate greatly because, as NASA has pointed out, the net effect of a water based planet is an average temperature which is controlled mainly by water evaporation leading to radiation absorbtion or emission.
Basically climate control on a planetary scale.
If there was a period of mountain building then volcanic activity would be higher and therefore climate gases would be higher - some cooling, some warming. But the net climate effects of the water cycle predominate.
The comments about "increasing the amount of rock weathering taking place" is quite frankly ludicrous. Even if this was the case there would be chance for many periods where the weather was far less and therefore the chance for a runaway scenario of warming would predominate. Your basically saying that the Earth has been lucky for about 500 millions years. Sorry but chance does not work this way.
If you take "weathering" in the modern context then there never has been a period of "weathering" as there has been in the modern era thanks to mining and farming. Just not credible.
There is no "CO2 predominates" ... CO2 is a minor gas of no great interest compared to many other gases.
The water cycle dominates everything.
If it didn't we simply and quite frankly would not exist.
Last edited: