How Many Trees Does It Take to Absorb CO2? Revisiting the Numbers
The calculations from both Sadhguru and The Quint on the trees needed to offset CO2 emissions from Rally for Rivers.
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In early September 2017, Sadhguru Jaggi Vasudev set out on a Rally for Rivers in a cavalcade of vehicles to raise awareness about India's dying rivers. While it is definitely a worthy cause, The Quint questioned the choice of vehicles in his cavalcade, which would lead to more air pollution, and consequently need many trees to be planted to offset the carbon dioxide emissions from the rally.
Sadhguru's team refuted the video with its own calculations, which said only a small number of trees would be required to offset the CO2 emissions from the rally, and questioned the sources of data used by The Quint and the method of calculation.
Sadhguru's team used data from the following link: http://www.truevaluemetrics.org/DBpdfs/Forests/Tree-Nation-Tropical-tree-sequestration-of-CO2.pdf
Sadhguru’s team claims that the total number of trees required to sequester the carbon dioxide from the rally is 2,506 trees based on the total of 33 tonnes of CO2 emitted (as the rally covered a greater distance of 8,800 Km than the 7,000 Km earlier planned).
The team’s calculation is based on the rally’s 30-day period with 13.166 Kg per month absorption of CO2 from fully grown trees that can absorb 158 Kg/year or 438 grams of CO2 per day.
This is what Sadhguru’s team’s calculations state:
A tree absorbs 158 Kg CO2 in a year (Source: http://www.truevaluemetrics.org/DBpdfs/Forests/Tree-Nation-Tropical-tree-sequestration-of-CO2.pdf)
The rally happens over a period of 30 days, a period over which the emission takes place. So absorption over a 30-day period needs to be taken.
158 Kg / 12 = 13.166 Kg per month.
Total Emission of the rally = 33 tonnes of CO2.
Total number of trees needed = 33,000 / 13.166 = 2,506 trees.
Why is there a huge difference in the number of trees that The Quint calculated would be needed and the calculation from Sadhguru's team? Here's why.
The Data Source
One of the data sources for the data that The Quint used is Arbor Environmental Alliance's figures. See link: http://www.arborenvironmentalalliance.com/carbon-tree-facts.asp
The data used by The Quint states that a single young tree can absorb 26 pounds or approximately 12 kg of carbon dioxide per year. That translates to 33 grams of carbon dioxide per tree per day.
We have used the figure for young trees assuming that most of the tree planting programme would have just started with this rally, and hence there would be trees that are less than a couple of years old at the most, and not fully grown trees.
Data from the US Environmental Protection Agency lists the method for calculating carbon sequestration capabilities of hardwood trees in an urban and suburban setting, further corroborating The Quint's data. See this link and screenshot below for trees up to 30 years of age:
Another document from Broward.org gives you the method for calculating the amount of CO2 sequestered in a tree per year. That document also quotes the following example:
The document shared by Sadhguru's team also gives the average figure for carbon dioxide sequestration by trees in a plantation setting as 25 kg per year in tropical conditions. See screengrab below:
The per vehicle carbon dioxide emission figures for the the Mercedes AMG G63 used in the calculations – 322 gms/km – was taken from the Mercedes website, while the figure of 171 gms/ km for the Mahindra XUV500 was taken from a Mahindra dealer's website in South Africa, because its not mandatory to report CO2 emission figures in India.
Basis for Calculations
Carbon dioxide emission per km of Mercedes G63 AMG: 322 g/km
Total distance to be travelled: 7,000 km
Tree absorption rate of carbon dioxide: 33 grams per day
Number of trees required to sequester 322 grams of CO2 in a day = 10 trees for every km.
Why 10 trees per km? Because for every km the vehicle travels these trees will need to absorb the C02.
Trees are immovable objects. While the Mercedes G63 AMG will continue moving ahead, kilometre after kilometre, it will emit 322 grams of CO2. For every km there will need to be 10 trees to absorb that CO2 in a day.
Assuming Sadhguru drives 233 km a day (7,000/30), the vehicle would be emitting 75,026 grams or 75 Kg of CO2 that day. That means it would need 2,273 trees along the route to neutralise the emissions from just the G63 for a single day. In 30 days of travelling it would need 68,205 trees, which we rounded off to 70,000 trees.
A similar calculation was done for 20 Mahindra SUVs.
Why are we using a single day, per km calculation? Again, trees are immovable objects. A tree in Kanyakumari cannot handle CO2 emissions in Himachal.
Why are we saying the CO2 has to be neutralised in a single day? Because unless you can take the same 10 trees along for the journey beside the vehicle, the math does not add up.
Our calculation shows how the rally would be completely CARBON NEUTRAL FOR EVERY KM if there were so many trees planted along the rally route – that is 7,95,454 trees totally along the route to neutralise the emissions from the Mercedes G63 AMG and 20 Mahindra SUVs.
Again, why a single day calculation? Because the next day the tree would need to absorb CO2 emissions from other sources.
Also, some trivia. The survival rate for trees is only 66%. See: https://timesofindia.indiatimes.com/home/environment/flora-fauna/Four-years-after-trees-are-planted-66-survive-Survey/articleshow/46450214.cms
Summary
It’s not just about mathematical calculations, it’s also about executional logic. Our argument is based on the facts that:
1. Trees need to be grown from saplings – hence we have used the average CO2 absorption of a young tree.
2. Trees are immovable – and hence the need to plant trees for every km of the route to absorb CO2 from the rally. The rally will move on but the trees will stay in one place.
One thing is for sure, trees are needed to clean up the air and to save India's depleting rivers. So go ahead and help make India green again in any way you can.
Links to Data Sources Used For Calculations
http://www.arborenvironmentalalliance.com/carbon-tree-facts.asp
https://www3.epa.gov/climatechange/Downloads/method-calculating-carbon-sequestration-trees-urban-and-suburban-settings.pdf
https://www.broward.org/NaturalResources/ClimateChange/Documents/Calculating%20CO2%20Sequestration%20by%20Trees.pdf
https://greenismything.com/2015/06/23/howmanytrees/
https://www.autodealer.co.za/new-cars/Mahindra/XUV500/Prices-Specs
https://www.mercedes-amg.com/en/vehicles/g-class/suv/g63.html
https://timesofindia.indiatimes.com/home/environment/flora-fauna/Four-years-after-trees-are-planted-66-survive-Survey/articleshow/46450214.cms
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