From Envirowiki

Back to Carbon capture and storage

To work out how much CO2 would escape at a 1% rate per year, you need to know how much was in storage, and how much is going in this year:

• T_n = (T_{n -1} + annual storage) * 99%

so, say there's 200 tonnes per year (it doesn't matter how much goes in, the fraction of the total is always the same):

• T₀ = 0
• T₁ = (T₀ + 200) * 99% = (0 + 200) * 99% = 198 (99%)
• T₂ = (T₁ + 200) * 99% = (198 + 200) *99% = 394.02 (98.51%)
• and so on...

after 40 years (T₄₀), sequestration stops, so the equation becomes simply:

• T_n = T_{n -1} * 99%

Because it's always a percentage of the previous year, it'll never reach zero, and it'll leak slower and slower each year after the first 40 (during the first 40 it leaks more every year due to the higher total).

Anyway, if you put it in a spread sheet you'll see that after 40 years, about 18% would escape, after 90, about 50%; after 140, 70%; after 250 years about 90%, etc.