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One person=how many trees to be planted by \| 09-09-2015 00:47
Planting trees and carbon offsets are great ideas. But unfortunately, there are a lot of things that cannot be undone. We cannot bring back the species whom we hunted down to extinction. Nor can we give back most of the land we took from the wild. However we can try and minimize the anthropogenic forcing on the climate and earth system today. To offset the amount of CO2 that we're presently adding, here's an average number of trees for you We'd need around 950 billion Gravellia Robustas or 136 of them for every person on earth. Or around 1 billion hectare of tropical pine and eucalyptus forest. That would be a dense forest as big as the size of Canada. But we need to take all these numbers with caution... The solution is at best, temporary. The CO2 sequestered just enters the carbon cycle. A forest fire, the forest dies, and all the sequestered CO2 is back into the atmosphere. The carbon inventory is not well understood. Sometimes it has been proposed that more carbon is present in the soil of forests than biomass above the soil. So forestation on these soils can disrupt the carbon sequestered and release it. CO2 sequestered may not mean lower temperatures. An important factor is albedo or 'whiteness' of the planet. Forests increases planet's albedo by helping in the formation of clouds. But forests also trap heat near the ground because of its dark canopies. So moving towards higher latitudes, canopies can actually raise the temperature even though they sequester CO2. So, every tree has a place if we do not want added trouble. We need to consider the effect that particular tree would have on the local ecosystem too. Planting of high maintenance trees might end up resulting in more CO2 added to the atmosphere. Now to get to those numbers, lets assume earth's radius as 6x10^6 m, and atmospheric pressure as 10^5 Pa. We get the total mass of the atmosphere to be around 4.5 x 10^18 kg (Atm. pressure x Surface area of earth = mass of atmosphere x gravitational acceleration). CO2 concentration projections in Mona Loa time series from NOAA's earth system research laboratory is shown below. Assuming we start planting the needed amount of trees today, and it takes 12.5 years for the trees to attain maturity, around 50 ppmv additional CO2 is added to the atmosphere. 50ppmv would be around 0.75 x 10^(-4) by mass percentage. (molar mass of CO2 is around 1.5 times average molar mass of air). So multiplied by 4.5 x 10^18 kg, we have 3.375 x 10^14 kg of CO2 added in 12.5 years. CO2 sequestered per tree or by a forest area depends on the species of the tree you're considering.Here is a relation taking into consideration some of the tree variables, CO2(kg/single tree) = 0.1676 x (Diameter at breast height)^(2.4799) Given by Myers and Goreau, a tropical tree plantation of pine and eucalyptus sequesters around 10 tons of carbon per hectare every year. That would be 33260.114 kg CO2/hectare/year. Assuming it absorbed at the same rate every year (which is not the case, rates are really slow in the beginning), we have 415751.425 kg CO2 absorbed in 12.5 years per hectare. So to absorb 3.375 x 10^14 kg CO2, we'd need .8118 billion hectares of forest. (Overlooking other carbon sinks) Presently we have 3.885 billion hectares of forests left. So that's an increase of 20.8% of forest area (It would be more than that since the forest absorbs slowly in the beginning, not all forests sequesters the huge amount of CO2, lot of present forests are already failing). So I guess it'd be around 25-30%. So that'd be approximately, 1 billion hectares. In number of trees, considering a 45 feet tall Gravellia Robusta, that sequesters 29.3 kg CO2 per year, we'd need to plant around 922 billion trees. On a safe side lets assume 950 billion. So that becomes 136 trees per person considering earth's human population to be 7 billion.

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