The biggest threat

IN his letter (February 26), Ultan Murphy claims atmospheric CO2 has increased by 0.004% since 1975.

The increase is in fact 16% (330 to 385ppm), and 48% since the industrial revolution (260 to 385ppm).

He is referring to CO2 as a percentage of the atmosphere. Does he think increasing a drug dose from 1gm to 10gm is only 0.01% and would make no difference?