By how much has Earth's atmospheric CO2 concentration increased ...

[jc611]

By how much has Earth's atmospheric CO2 concentration increased since the year 1800?
 
  What will be an ideal response?

Question 2

How do we know this?
 
  What will be an ideal response?

[mtmmmmmk]

Answer to Question 1

389 ppm  280 ppm = 109 ppm (answer written in 2009)

Answer to Question 2

Keeling's data show that the mean atmospheric CO2 level for today is around 389 ppm. The ice core measurements show that the preindustrial CO2 concentration (the value circa 1800) was about 280 ppm, so the CO2 concentration has increased by 109 ppm.

The average rate of increase in the CO2 concentration since 1800 has been 109 ppm/209 yr, or about 0.5 ppm /yr.