Robin –
” Most atmospheric CO2 comes from the tectonic subduction of limestone, so there must be some natural process converting CO2 back into limestone ready for its’ next time around. That would seem to be important. ”
Pardon?
Most subduction (the word “tectonic” is surplus here) is of ocean-floor plate below other oceanic crust or below continents, so basalt under basalt or granite respectively.
However that does drag wet sea-floor sediment down with it, and that is source of the gases and water-vapour from the resulting volcanoes. Not limestone! The water seems also to act as a flux, helping some of the subducted rock to melt into magma that oozes its way upwards to erupt as volcanoes or solidify underground as “batholiths” (lit. “deep rock”) such as Central Cornwall.
Even where the heat and pressure of this “igneous intrusion” metamorphoses any nearby limestone into marble that rock is still calcium-carbonate, although carbonaceous materials trapped within it in its sedimentary deposition phase are distilled out, sometimes leaving the marble as nearly pure CaCO3.
Crustal-rifting volcanoes (e.g Iceland) and Mantle-plume volcanoes (e.g. Hawaii) are all of igneous, Mantle rock, primarily basalt, with little gas.
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As for your proposed “golden age” of using all the coal we can still extract until it’s all gone, the danger of it was recognised about 100 years ago but largely ignored. I suppose the limit was predicted to be so far ahead, in an era of assuming we can “tame Nature” if only we throw enough Scientists and Engineers at her, that few would have believed it. That was when coal was the primary industrial, transport and domestic fuel and chemical feedstock, and calculated on contemporary reserves and consumption rates.
And when it’s gone, it’s gone: oil first, then coal. Ummm, then what?
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Yes we do need understand natural mechanisms, but so we can understand just how much of a mess Man has been making of them, not just in the last 2 or 3 Centuries but for some thousands of years. Not the climate, no, for most of that time, but certainly in other ways; steadily growing since the dawn of settled agriculture.
Indeed, a huge amount of research into the Quaternary* climates has already been done, and continues, so we can determine what the Earth might have done if Nature had had it all her own way, then determine Mankind’s influence and try to forecast future effects.
These are not easy questions to answer, and finding suitable, practicable responses is far harder still, but ignoring those and wanting to use the rest of the petroleum and coal just because they are there, will not help anyone.
We have been burning these for a long time, but have they brought a “Golden Age”, and what sort of “Age” will follow them?
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*Essentially encompassing the present Ice Age so far, and the evolution of our own species.