Planting 1.2T Trees Could Cancel Out a Decade of CO2 Emissions

I can tell you how I reason to it.

According to many sources, but I will cite this one[1] a single tree converts about 50 lbs of CO2 in a year. There are three trees on my property, a city tree (planted by the city) and two Birch trees planed by the original developer. All are deciduous so lose leaves in the winter but we'll give them full credit anyway, so call it 150 lbs of CO2 a year.

My rooftop solar system nominally puts out 5.2 kW of power under full sunlight, although efficiencies cut that down to around 4.8 kW net into the grid. I have over 10 years of data from the system, drilled down though it averages out to about 4.5 "solar hours" per day with an average daily output of about 22 kWH per day or about 8 MWH per year.

The US Energy Information Association (EIA) tracks a number of statistics, but the one that is most relevant is the number of metric tons of CO2 per MWH per state. You can see California's number in this report : https://www.eia.gov/electricity/state/california/ is 474 lbs per MWH.

Using that number, my rooftop solar system "saves" (which is to say doesn't generate) about 3,792 lbs of CO2 a year. Which, is way more than the 150 lbs a year the trees are taking out of the air. This is why the 1.2T trees, or 160 per person, is such a large number. A family of four would need to plan 640 trees on their lot, which would remove 32,000 lbs of CO2, which is a lot. To match my solar panels I would need to plant an additional 76 trees.

What you can take away from that is that solar panels in places where you can't put trees are a solid alternative. And planting trees rather than letting unused land sit idle as a field of grass is also a good plan. As a home owner, solar, even in places where it won't generate all your energy needs, will help cut CO2 emissions.

[1] https://projects.ncsu.edu/project/treesofstrength/treefact.h...

It can be shown both bottom-up and top-down, but I prefer the bottom-up: Photosynthesis is usually an order of magnitude more efficient than photovoltaics: https://en.wikipedia.org/wiki/Photosynthetic_efficiency

...an individual leaf might be peak out at 3% efficient, but it is operating just a portion of the year (maybe about a third to a half at full performance) and also much light gets reflected, absorbed by branches, or misses the leaves entirely.

Additionally, photovoltaics peak at 40% efficiency but get about 15-20% efficiency typically and can function the entire year (unless fully covered by snow). And they're displacing electricity produced primarily from fossil fuels which are burned at 30-40% efficiency.

Now from a top-down perspective: forests (in this case calculated by replacing cropland with forests) are estimated to sequester about 2 to 10 tons of CO2 per acre per year. https://fas.org/sgp/crs/misc/R40562.pdf

In principle, an acre of about 40% solar photovoltaic system with a 25% capacity factor could produce about 3.5GWh per year. But typically, about exactly one tenth that is done in practice: 0.35GWh/year/acre.

Since you'd be displacing electricity from the US grid, which is currently about 420 grams of CO2 per kWh (based on my calculations of the most recent eia.gov figures, but you can find similar figures by Googling), that's equivalent to 147 metric tons of CO2 per acre per year for typical photovoltaics (and over 1000 metric tons per acre per year in the idealized case).

This person's calculations reach similar conclusions: https://www.solarpowerrocks.com/environment/installing-solar...

So absolutely, it's better to use solar panels than trees, at least until the grid is fully or nearly-fully saturated by solar.

...BUT once we fully clean the grid, trees have some advantages: 1) they efficiently suck CO2 out of the air and store it, not just produce the energy. That means you can actually draw-down CO2, producing negative emissions. 2) They're scalable. A tree is like a solar farm, CO2 direct air absorption system, and a chemical factory but can be planted as just a seed. It may not be "efficient", but being self-replicating and scalable is pretty powerful.

In my native Sweden (where it can be quite sunny in summer but not so much in winter) there is a concept of a "care tree", living up close to the manor of a yard of farm. [0] (link in Swedish, sorry, perhaps try Translate)

I am now living in Monrovia, Liberia, where you will often find large trees for shade, often mango, sometimes moringa or coconut. There's also a bougainvillea shading a bench in every village between Monrovia and Yekepa. :-)

Edit: I also want to mention the concept of agroforestry [1], a part of permaculture agricultural design principles, where trees (often fruit bearing) are used with lower vegetation, shrubbery and crops, creating a food forest. Incidentally, this is what farms often look like in West Africa, with coconut, banana, cocoa, papaya, cassava, etc growing intermingled on the farmland.

[0] https://sv.wikipedia.org/wiki/V%C3%A5rdtr%C3%A4d [1] https://en.wikipedia.org/wiki/Permaculture#Agroforestry

> More pressingly, when it comes to plant life RIGHT NOW, we're still dangerously close to CO₂ starvation levels.

This is the most provocative claim you make and coincidentally the one you don't back up with any evidence. The one article you post from phys.org (1) does not use the colorful and misleading language of CO2 'starvation' and (2) actually concludes the opposite of the less dramatic point (plants will be better off with more CO2):

> But, as we know, C3 plants waste a lot more resources at higher temperatures, so any increase in photosynthesis from rising CO₂ levels seems likely to be at least cancelled out by the effects of the global warming it will cause. And that's without factoring in changes to rainfall patterns such as more frequent droughts. Solutions that seem to be too good to be true generally are – and, for the moment, that still seems to be the case for the idea that CO₂ enhanced crop yields will feed the world.

However the idea of being in a CO2 'famine' was recently brought up by the head of the Presidential Committee on Climate Security, William Harper, and also does not seem to be backed by any evidence or the scientific community:

> "It's a silly argument," added Britton Stephens, a senior scientist in the Earth Observing Laboratory at the National Center for Atmospheric Research, in an interview.

> Both independent academic institutions and government agencies around disparate parts of the globe have concluded more carbon dioxide will "bring many negative impacts" to plant environments, Stephens emphasized. "If someone is going to claim it's good, it's incumbent upon them to show evidence." [0]

I mean just using common sense plants can and clearly have thrived with lower levels of CO2, before the far bigger threat of human deforestation decimated forests and plant life. The issue isn't whether plant life will be slightly better off with more CO2 or not, but what negative effects changing climate will have on crops, which could be catastrophic and is the point the phys.org concludes with.

This seems like just another flavor of a very similar climate change denialist argument that there was higher CO2 levels during previous glacial periods, also debunked [1].

[0] https://mashable.com/article/trump-climate-panel-william-hap...

[1] https://www.skepticalscience.com/co2-higher-in-past-intermed...

One analysis I read some time back claimed that Trees are net positive when they are closer to equator, IIRC 30deg each way. fortunately for this topic, the areas close to equator are also significantly poorer countries thereby maximizing the roi of a fixed dollar expense.

Overall I believe that if a functioning carbon credit marketplace is established we can fund the whole green movement with a fraction of world GDP and might even end up creating a whole bunch of jobs doing it.