There has been a lot of media attention in recent weeks devoted to “natural climate solutions”—various ways by which we can reduce the potential for damaging climate change by the better management of forests and agricultural soils. Preventing deforestation and planting trees top the list of favorable activities. There are few easier ways to remove carbon dioxide from Earth’s atmosphere than by the process of photosynthesis, which converts carbon dioxide into cellulose and other plant fibers, some of which can store the carbon for centuries. Better management of agricultural soils may also play a small role in enhanced carbon storage increasing the various substances that make up soil organic matter. Neither trees nor soils can do the entire job, but there are a number of reasons why more forests and more soil organic matter are good for the environment, not the least of which is the preservation of biodiversity.
Our house is entirely powered by solar panels, which provide electricity that might otherwise be generated by a coal-fired power plant. Each year, we use about 3100 kW-hr of power, which would release about 1400 lbs (=0.7 tons) of carbon (as carbon dioxide) to the atmosphere. Since inception four years ago, our solar array has generated 33,600 kW-hr, which SunPower tells us has prevented the addition of 25.5 tons of carbon dioxide (= 7 tons of C or 1.75 tons C/yr) to the atmosphere. Our excess generation of electricity goes to the grid.
Question is: would we be better off using power from the grid and planting the area now occupied by the solar panels with trees to soak up the carbon dioxide from burning coal?
To provide a liberal estimate, we have 27 m2 of solar panels that occupy an area that is approximately 50 feet x 200 feet (0.23 acres), calculated to include the open space that we need to prevent them from shade. In the eastern United States, forests typically accumulate about 2 metric tons of carbon per hectare during each year of growth. That is equivalent to 0.81 tons of carbon/acre. So, the area occupied by our panels might otherwise accumulate about 0.18 tons of carbon as carbon dioxide, each year, if it were planted with trees.
The benefit of solar panels must be discounted by the small amount of carbon dioxide that is added to the atmosphere during the mining of materials, manufacturing and fabrication of solar panels. (See: https://blogs.nicholas.duke.edu/citizenscientist/our-experience-with-solar/ ). Solar panels also involve an up-front initial investment, which is paid off by avoiding electric bills in subsequent years. Even so, solar panels seem to have an edge over trees, and it is important to remember that trees don’t live and grow forever.
It will take a major transition to renewable energy, like solar, to stem the release of fossil carbon to the atmosphere, from which there is no good, long-term way to remove it.
References
Griscom, B. and 31 others. 2017. Natural climate solutions. Proceedings of the National Academy of Science doi: 10.1073/pnas.1710465114
Schlesinger, W.H. and E.S. Bernhardt. 2013. Biogeochemistry: An analysis of global change. Academic Press/Elsevier, San Diego.
Schlesinger, W.H. 2018. Are wood pellets a green fuel? Science 359: 1328-1329.
Love this blog post! But why not say “perennials vs. solar panels”? Perennial grasses are doing the same things that trees are doing, but putting more of the C below ground, so perhaps keeping it safer while also “improving agricultural soils” that are currently being degraded by fossil-intensive annual row cropping. Grasslands could protect these soils, soak up atmospheric carbon, and also produce meat (and possibly grain https://landinstitute.org/our-work/perennial-crops/kernza/). I started off in forestry because trees are my passion, but switched to perennial grasses because they can be managed for agronomic products on land currently in row crops, thereby giving humans more incentive to grow them and scrub the atmosphere at the same time.
Wonderful article about the complexity of human and natural impacts on the environment. Questions: What difference if any does the species of the tree have on the amount of carbon sequestered? Or the live of the tree in that species? Does it matter that oaks grow slowly with long lives but have highly compact wood as opposed to poplar trees which grow as fast as weeds, live shorter lives, and have a very mushy wood. Needles v. Leaves. Do root systems make a difference in these processes? Would harvested timber which becomes incorporated into furniture, house framing and floors add to the sequestration equation for forests? And does the cost and impact of decommissioning (disposal) of the panels subtract from their advantage. Are there microclimate impacts from the fact that the sun’s rays are used by the solar panel rather than the surrounding habitat? Are there long term non global warming impacts from the mining operations and the manufacturing processes which create a Faustian Bargain? Great article. Keep up the good work.
Dear Professor Schlesinger,
Your analysis is informative and you begin by pointing out that natural approaches are beneficial because they remove carbon from the air; however, then you seem to suggest that we need to make a choice between renewable energy and nature. I strongly believe that with the situation we face we must embrace all possible technologies to mitigate climate change. Recent data indicates that even in the USA emissions have bumped up. It appears unlikely to me that the nations of the world will be able to reduce emissions sufficiently to reach the goal of keeping the global temperature rise to 1.5 degrees C, and we are already in a dangerous temperature zone. We need to be aggressively pulling carbon from the air and embracing negative emission technologies (NETs) as well as clean energy. Recent research found that natural solutions like improved management of forests, wetlands, grasslands and engaging in regenerative agricultural can remove about 5.6 gigatons (Gt) CO2e of carbon per year by 2030. Natural approaches also carry numerous co-benefits, from improving soil and water quality and increasing food security to protecting biodiversity. By 2050, the world will need to sequester and store 8 GtCO2e annually on average—removing more emissions than the total U.S. GHG emissions in 2015 (6.6 GtCO2e). Between 2010 and 2100, the world will need to store about 810 GtCO2 cumulatively, the equivalent of about 20 years of global emissions given current rate.
This will not be easy and millions (even billions) of people around the world will need to be involved, but I don’t think we have a choice.
References:
Minx, J. C. et al., Negative emissions—Part 1: Research landscape and synthesis, 2018, Environ. Res. Lett, 13 063001.
Fuss, S., et al., Negative emissions—Part 2: Costs, potentials and side effects 2018, Environ. Res. Lett. 13 063002.
Levin, K, Mulligan, J. and Ellison, G. (March 19, 2018), Taking Greenhouse Gases from the Sky: 7 Things to Know About Carbon Removal, World Resources Institute. Retrieved from (https://www.wri.org).
We need to pull out all stops to mitigate climate change, but in our specific case in Maine, the solar panels won.
Hi Bill,
When you write about “excess generation” going to the grid, are you also covering 1/4 of the fossil fuel usage for a similar house, so you’re providing a service for your neighbor? Do you earn revenue from the excess thereby accelerating the payoff of your panels while providing clean power to your neighbor? You should get Double Planet Points!!
We need to name these services so people can feel proud and earn their Planet Points.
For a DUKE MA, I gave a couple names to the idea of business restoring ecosystems as they produce their revenue. My work is farming macroalgae (seaweed) for carbon-neutral fuel and co-products. The activity removes CO2 from surface waters of oceans that cause ocean acidification. I call the positive ecosystem activity “Restoration of the Commons” since we should all be tired of the “Tragedy of the Commons.” For the business folks, I offer the term “Restorative Commerce.” A name means existence! (Myers, Alyson (2015), Macroalgae Farming: A Strategy for Economic Growth and Nutrient Mitigation).
Thank you for quantifying one mitigation strategy (trees) against another (panels). We must take multiple positive actions…as fast as we can. Trees, panels, macroalgae…and more. Thank you for your column.
All best,
Alyson Myers
President, FearlessFund.org
PI, Ocean Energy from Macroalgae (funded by DOE ARPA-E)
Duke 2015
It’s unlikely the solar panels will ever lose to trees in this game. But in a different part of the continent, and with a different species of tree (e.g. loblolly pine), it would be a better contest!
I calculated the balance between solar and trees from my experience in Maine. Kim is right that in the Southeast, forest growth is closer to 4 tons C/ha/yr, so carbon uptake would be larger. But, the energy capture by solar panels would be greater too. We’d need to do a similar balance for that region.