I was intrigued with a thought about “when did CO2 atmospheric concentrations actually become directly harmful”, i.e. we’d really really have to do something about it as human beings.

From here – http://www.uigi.com/MSDS_liquid_CO2.html:

“Carbon Dioxide is a powerful cerebral dilator. At concentrations between 2 and 10%, Carbon Dioxide can cause nausea, dizziness, headache, mental confusion, increased blood pressure and respiratory rate. Above 8% nausea and vomiting appear.  Above 10%, suffocation and death can occur within minutes.”

Let’s assume then that 2% is unacceptable.  Our current concentration on 1 April 2010 is 391 ppm. From the Mauna Loa record – http://www.esrl.noaa.gov/gmd/ccgg/trends/ – we can see that over 50 years the average growth rate is 1.43ppm/year.  One notices that recent rates are higher, i.e. the average of the past 10 years is 1.98ppm/year.  I’ll just take 2ppm/year.

Thus we need to estimate when we hit 20,000ppm.  That’s 10,000 years hence, i.e. 12,010 AD.

We could halve that probably, i.e. 6,005, as I’d reckon we’d definitely notice 1%. So CO2 is a long way off killing us, except it’s likely to destroy us in fifty years if we do nothing. That’s the long and the short of it.

[I can’t afford to pay, but you can afford to look at the black humour side of this here – https://www.cartoonstock.com/directory/c/carbon_monoxide_poisoning.asp]