Hi Robert,
Very interesting figures. When I was a boy back in the 1940-50s, the CO2 concentration was 0.03% or 300ppm. If we say that was 60 years ago, then the latest figures indicate a rise of ~30% in that time or, if we average it out, increasing by 0.5% pa. or 50% every 100 years. Extrapolating that number, the world could expect a CO2 concentration in ~2050 of ~0.045%.
(Hope my maths measures up ok
)
Robert