421 parts per million CO2 in the world's atmosphere

The Associated Press is distributing the terrifying news that an increase of a harmless gas that makes up 4/100 of 1% of the earth's atmosphere is driving the uncomfortable warmth of some parts of world.   That would be akin to saying that the temperature of an Olympic swimming pool, which contains 660,430 gallons of water, would be raised significantly by the addition of 264 gallons of water. If the temperature of the water in the pool was 75F and the temperature of the added water was 85F the temperature of the pool water would increase an undetectable amount.