Confessions of a carbon sequestration skeptic

One of the potential environmental benefits that came up in our discussion of the pro’s and con’s of turfgrass was carbon sequestration.  The basic premise of carbon sequestration is to take CO2 out of the atmosphere and ‘lock it up’ in a form that won’t contribute to further global warming.  One of the fallacies floating around these days is that any plant that photosynthesizes, takes up CO2 and thereby sequesters carbon.  What we need to realize is that leaves give off CO2 at night via respiration and all non-photosynthetic (non-green) plant parts such as roots and stems give off CO2 virtually all the time.  Turfgrass has some potential to sequester carbon, primarily as soil C. If we consider that a 7” deep layer of soil weighs 2 million pounds, increasing soil carbon by 1% can sequester 20,000 lbs of C per acre.  How long does it take turfgrass to increase soil C by 1%?  Don’t know, but I’m sure it takes awhile.  Also, there is a limit to amount of carbon a give soil can store as C is respired away by microbial activity so eventually a steady state will be reached.  (Plus we haven’t even subtracted out fossil fuel carbon to maintain turf).  Some plants, such as trees, do have the capacity to sequester carbon in wood for long periods – think redwoods, sequoias and redcedars.  But these trees cover only a small fraction of the world land area.  Intensively managed forestry plantations can take large amounts of carbon out of the atmosphere and sequester it into wood.  The question then becomes what do you do with the wood?  If we burn it for biomass energy; Foof! All that C is right back in the atmosphere.  Still better than burning fossil fuels but also a little less than carbon neutral at best.  We can build houses with the wood from the plantation – the carbon will be sequestered as long as the house lasts.  My home and barn were built in the 1890’s so the carbon taken out of the atmosphere by those trees is still locked up.  If we really want to get serious about carbon sequestration, however, our best strategy would be to convert the entire Upper Peninsula of Michigan to fast growing poplar plantations, harvest the wood every 15 years, and sink the logs in Lake Superior where the cold water will prevent decay.  Sound funny?  I’m not the only person thinking this way.  See Strand and Bedford 2009. Ocean Sequestration of Crop Residue Carbon: Recycling Fossil Fuel Carbon Back to Deep Sediments Environ. Sci. Technol., 2009, 43 (4), pp 1000–1007.  


Bottom line: carbon sequestration is a very complex process and sequestering carbon for more than a few decades takes more creativity and brain-power than most of us can muster.  However, trees and landscape plants do have important role to play in mitigating climate change and it doesn’t require heroic feats of engineering.  Trees and landscape plants can effectively cool buildings, thereby reducing air conditioner use and save fossil fuels – see the USDA Forest Service Urban Forestry Research site for a few examples   ultimately this is landscape horticulture’s contribution to climate change.  Carbon sequestration?  It’s a drop in a very big bucket.


10 thoughts on “Confessions of a carbon sequestration skeptic”

  1. I’ve been following the efforts to breed blight-resistant American Chestnut trees for years now, and those efforts are now reaching the stage of studying the best ways to re-introduce the species to Appalachian forests. A press release from Purdue last year touted the Chestnut tree’s potential for carbon sequestering, given its fast growing nature, and its potential use as a hardwood for construction and furniture. Hype or hope? Press release here:

  2. Thank you Bert for posting this! I have been arguing with people for years about how carbon sequestration on a large scale is almost a fallacy. The land cover over the entire earth changes almost constantly. As one region is converted to agriculture, another field goes fallow elsewhere, and things stay the same. We can plant all the trees we want, but until we figure out a way to harvest those trees and convert them to a usable product without releasing more carbon back into the atmosphere, we are right back to square one! My limited brain capacity can’t begin to solve this problem, but I am glad that somebody else posted it in a way I couldn’t.

  3. There’s lots of ways to look at this. On one hand, you can say any sequestration is better than none. But I think a reality check is in order. If you look at the info cited in the Strand and Bedford article, up to 6 Petagrams (a petagram is 10 to the 15th grams) of carbon is released to atmosphere annually. As John K notes this is more than most of use can get our minds around – but clearly it will take a huge systematic effort for sequestration to make a dent. Personally, I think Strand and Bedford are a little quick to dismiss forest plantations (my forester bias again). Plantations can sequester carbon in wood and also increase soil C. They key, of course, is what do you do with the wood?

  4. This taps into one of my concerns, which is the increasing popularity of taking the “waste” left over from harvesting plantations and burning it as a “biofuel.” There’s even an effort to use arborist wood chips the same way. Why people think that burning these materials is environmentally friendly, rather than leaving them on site as a mulch, is beyond my comprehension. (And Ginny, you’ll be amused to know I started a Facebook group several months ago called “I will never give up books until you pry them from my cold dead hands.”)

  5. My take as a forester…. for more years than I care to admit I’ve looked ascance at enviromentalists promoting tree planting and reforestation as sequestration. It’s an weasy way to jump on the band wagon and it actually sounds like it works.

    Then the paper and lumber companies with their tree plantations jumped on the bandwagon and touted how thier activities helped. A PR bonanza!

    The majority of forestry planted trees are pre-scheduled for destruction (and carbon release)… those heading to the paper mill have a very short life as a sequestration agent. Those heading to the sawmill probably are only good for a couple of decades at todays rate of building turnover.

    Then what about all the carbon those urban tree planting programs are sequestering? Whats tha average life span of an urban tree… 7 years?

    Come on folks, the best sequestration scheme we got going is the local landfill. Think of all the paper, old lumber, yard waste tree trimmings etc. that are burried in anaerobic landfills. They are literally sinks of hard carbon that will stay hard carbon for a long, long time.

    Think about it folks. These repositories will be coal and oil deposits in a few million years. And think of all the interesting “fossils” the creatures of the distant future will unearth and marvel over.

    Just some thoughts of an old forester.

  6. Wes, you’ve touched on another one of my chronic complaints – urban street tree life span. Several years ago, the average street tree life in Seattle was 8 years. You’ve seen me ranting on this blog (and other places) about poor quality roots, improper planting practices, and lack of appropriate aftercare as some of the big reasons urban trees don’t make it. I have to just look the other way when the big PR efforts are made to plant trees – usually by volunteers, often school children, who have no idea what they are doing.

  7. Aaaahh! Not urban tree planting too! As a forester (and an urban one to boot!) this is near and dear to my heart. Most of our trees do great, but the few each year that don’t survive the initial planting shock bring the average down. I think the average street tree (not counting tree pits) is much higher than 7-8 years, but eventually they become wood chips and all of the machines needed to remove one tree must offset the carbon sequestered anyway, right? This is the kind of thinking that has me chasing my tail most days.

  8. Maybe if we plant a lot of poison ivy. It, apparently, loves the increased CO2, and nobody is gonna burn it. Think thousands of thigh-sized hairy vines guarding against human intrusions into natural forests. Win-Win! /s

  9. I too spent a couple of years classified as a community forester. I still disagree with your sceptacism about the average age of urban trees.

    The following excerpt comes from a publication titled, Urban Forest Health: identifying issues and needs within the Northeastern Area.

    “Some Facts
    Increased awareness of the benefits provided by trees has stimulated public interest and financial support for urban and community forestry programs and tree planting and care projects. Despite this, many urban forests are not thriving:
    Urban trees reach maximum potential for environmental benefits after age 30, but the average life-span of a downtown urban tree is less than 10 years.

    Most cities are removing more trees than they are planting.

    Thirty seven percent of cities practice “crisis management” – responding to accidents, impending hazards, and complaints rather than implementing a systematic tree maintenance program.”

    To be sure there is more to the issue than average lifespan, but we must face the fact that to date urban forest programs have performed poorly in creating a healthy and thriving urban forest base…. especially in the
    “downtown areas referred to in the quote above.

    Trees have always been dear to my heart, but I believe we must face the facts in order to react appropriately. And we should avoid the impulse to propagandize issues.

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