Just as a point of note, did you know that the "official" place where CO2 is measured to be a global average is atop a big dormant volcano in Hawaii...that is constantly seeping lots of CO2 into the air from the cinder ash all over it?

Get hold of a gas analyser and measure it yourself on Salisbury Plain, Dartmoor, Snowdon or Scafell Pike snd I guarantee it will be approx 310 to 340 ppm.