Originally Posted by BrokenArrow:
“I don't know.”
I sense a theme that is likely to be continued...
Quote:
“But the history of the Earths atmosphere over geological time show that it started off very similar to Venus....ie 98% CO2 at around 90 bar pressure.”
And before the Hadean eon, with global temperatures of around 230C, the Earth was a ball of molten rock. I don't think you would have enjoyed either of those options very much.
Quote:
“CO2 levels have been reducing linearly over time and present day levels are the lowest they have ever been in terms of the geological timescale.”
Well, no, they haven't been "reducing linearly over time", they aren't the lowest they have ever been, and trying to smudge out the variations in CO2 which are closely correlated to climatic changes throughout the Earth's history by appealing to "the geological timescale" is a conjuring trick so inept that nobody is going to fall for it. Well, the Eel might.
Quote:
“They are probably at the lowest they can go without extinguishing life, I seem to remember 0.02% being the level at which plants really start to die off.”
Those are levels seen only during glacial periods. You may have noticed that we are not currently in a glacial period. The pre-industrial CO2 level was around 280 ppmv, and that was about the level that had persisted throughout the Holocene, during which all of human civilisation evolved. It didn't seem to be a problem then, and we won't in any case see those levels again for thousands of years.
Quote:
“If we are to believe that the current minuscule rise in CO2 due to human activity really is to blame for global warming, then the above facts give a much more worrying inconvenient truth, the SUn has been getting hotter linearly over the same period and the Earth has run out of the stuff that is used to regulate global temperatures.”
There is nothing "minuscule" about a >40% rise over pre-industrial levels. And we are not "running out" of CO2 - the mechanism by which this will happen in the distant future (a billion years or so hence) is via the silicate weathering thermostat. It will be a toss-up between whatever life remains on the surface being burned to a crisp, and photosynthesis ceasing to be viable.
So your concerns are hopelessly misplaced. Warming
now is the problem. Too much CO2 in the atmosphere is the cause.