The answer? Almost 467 billion!
I was looking through the EPA’s Inventory of Greenhouse Gas Emissions and Sinks (yes, I peruse reports like that out of pure interest; what of it?) and saw that, in 2013, the U.S. offset 881.7 million metric tonnes of greenhouse gases (GHGs) through “sinks” (such as forested land that naturally sequesters carbon). That’s 13.21% of total (not net) U.S. emissions for 2013! So, I started wondering more about naturally sequestering our carbon emissions with trees. How many trees would it take to sequester all of the CO2 we emitted in 2013? Would it be possible to do that? Could we do it if every city or town in the U.S. planted an acre of trees?
Let’s take a look at the numbers:
- Total US GHG emissions in 2013: 6,673,000,000 metric tonnes CO2-equivalent
- Total US CO2 emissions in 2013: 5,505,200,000 metric tonnes CO2 (Let’s use this number, since the research on sequestration by trees is based on CO2 absorption only, rather than methane, nitrous oxide, sulfur dioxide, and other GHGs)
Now on to the trees:
- CO2 absorbed by 1 young tree per year: 26 pounds (Let’s assume they’re all young trees since they would be newly planted.) (Source: Arbor Environmental Alliance)
- Average number of trees per acre: 700 (Source: Tufts University)
- Amount of CO2 absorbed by 1 acre of trees per year: 8.255 metric tonnes CO2
So, how much forested land is needed to absorb our annual CO2 emissions?
- Number of acres of trees needed to absorb all US CO2 emissions: 666,892,792 acres
- Number of square miles of trees needed to absorb all US CO2 emissions (640 acres per square mile): 1,042,019 square miles
- Size of United States: 3,805,927 square miles (Source: US Census Bureau)
- % of US land needed to absorb all CO2 emissions: 27.38%
That’s a huge chunk of land that would need to be set aside to be planted with trees! Could we make a dent in that by having each city or town in the U.S. plant an acre of trees?
- Number of incorporated areas in the U.S.: 19,509 (Source: US Census Bureau)
- Amount of CO2 absorbed if each area planted 1 acre of trees: 161,054 tonnes of CO2
We’ll definitely need more than that! So, could we even set aside enough land to sequester all of that CO2? Well, the federal government only owns almost 28% of U.S. land (Source: USDA
), so it would actually require setting aside all federal land and planting it with trees (and I’m betting a good chunk of federal land is already covered in protected forests).
How is our land actually being used? Only 2.6% of all U.S. land is urbanized and another 4.2% is rural residential land. A whopping 52.3% is used for agricultural purposes (e.g. cropland, grassland pastures, range, and forested grazing land). Another 21.9% is forested land used for timber, and 13.1% is categorized as “special use” land, which includes wilderness and wildlife areas, national and State parks, and national defense and industrial areas. The remaining 5.9% is taken up by miscellaneous land uses (Source: USDA
). So, we do have a good amount of forested land in the U.S., but most of it is being cut down for timber. And, we don’t have an excess supply of unused land lying around just waiting to be planted with trees.
So to answer my question: It would take almost 467 billion trees (or almost 667 million acres of forested land) to absorb all U.S. CO2 emissions. That number is a bit smaller since we already have some forests providing carbon sinks. But, it would still take a large number of new trees. Theoretically, we do have the land for all of those trees, but – practically – it would require displacing other land uses, primarily agriculture and timber. I won’t say it isn’t possible, though…