By BMA estimation, all the trees in Bangkok can absorb CO2 no more than 500 tonnes/day which accounts for only 0.5% of all CO2 released in Bangkok. By the author’s rough estimation, based on Bangkok’s population of 10million, Bangkokian’s CO2 footprint as estimated by BMA is 7.3 tonnes/person/annum will total approximately 73million tonnes/annum. A large tree absorbs 20.3 kilogrammes per year. Therefore, Bangkok needs at least 3,080,168,780 full grown trees to reach a CO2 neutral state. An average full grown tree with 8 metre crown diameter covers an area of around 60 square metres. Therefore, Bangkok will need a planting area of 184,810 square kilometres to be CO2 neutral. It is worth nothing that the total area of the whole country is only around 500,000 square kilometres.