answered on 16 Mar 2020:
last edited 16 Mar 2020 8:50 am
Check out this study (https://science.sciencemag.org/content/365/6448/76) which modelled the effect of planting a large number of trees on CO2. The study showed that by planting more than half a trillion trees, 25% of CO2 in the atmosphere could be removed. So 20 million trees would hep to remove some of the CO2 from the atmosphere yes!