2.6  CO2 emissions last 500 years

A rapidly rising CO2 impulse spike has effects that last more than 500 years

Graph A shows the response to an instantaneous +50 ppm & -50 ppm CO2 impulse spike.

This graph assumes there are no other ongoing CO2 emissions after the initial impulse spike.

This graph shows it will take 500 years for the effects of a small 50 ppm impulse spike to reduce to 20% of its initial maximum level. 

So an ~80% drop in CO2 concentration takes 500 years!

Therefore, a 50 ppm impulse spike reduces to about 10 ppm after 500 years.

So what does this mean for a 417 ppm impulse spike?

It means that because of the use of fossil fuels worldwide to date, the Earth's Atmospheric CO2 concentration is unlikely to drop below 330 ppm until after the year 2500 !

And that's ONLY IF we stopped adding more CO2 emissions to the Earth's Atmosphere from fossil fuel use RIGHT NOW in the year 2021 !  But that's not possible.

Decay of atmospheric CO2 perturbations:

(A) Instantaneous injection or extraction of CO2 with initial conditions at equilibrium. Response to an impulse spike in CO2

(B) Fossil fuel emissions terminate at the end of 2015, 2030, or 2050 and land use emissions terminate after 2015 in all three cases, i.e., thereafter there is no net deforestation.

REF: Assessing ‘‘Dangerous Climate Change’’: Required Reduction of Carbon Emissions to Protect Young People, Future Generations and Nature – Dec 2013 - doi:10.1371/journal.pone.0081648.g004 – James Hansen et al