(Please include reference for every answer (website/article etc) Please do not copy paste answers from internet.

(Please include reference for every answer (website/article etc) Please do not copy paste answers from internet.

1) What is the approximate concentration (in units of parts per million, ppm) of CO2 in the atmosphere during pre-industrial times?

b) Provide an estimate for the current concentration (in ppm) of CO2 in the atmosphere.

c) Explain why there is a difference between part a and b