Just under six hours
if your value of 20MT is true, but it isn't. Estimates for the Pinatubo eruption are in the area of 0.04 to 0.05 GTonnes of CO2. Twice your estimate. Pinatubo was a VEI-6. I produce more CO2 in explosive dumps after a vindaloo curry.
Humans produced well in excess of 30 GTonnes per annum CO2 in 2010. That's a factor of 700.
Let's see if we can help your confusion! Pinatubo produced 40-50 MILLION tonnes of CO2 during the eruption. Humans produce over 30 BILLION tonnes of CO2 per annum.
I'm not an expert but I was a scientist, so I check multiple sources and estimate the provenance, consistency and authority of the data. And then I read it - properly - and then I draw my own conclusions.
Even VEI-7 eruptions like Krakatoa and Tambora, which occur one in a century, will only generate 0.1GTonnes. That's 100 MILLION.
If we get a VEI-8 then we'll probably get a measurable CO2 increase in the atmosphere but CO2 will be the least of our worries.
Suck it up.
You know, I did originally say a week but I forgot what units I was working in... Goes to show that you really should check everything and trust no-one.
