# how much reforestation for reducing greenhouse gases **URL:** \ **Category:** Factual Questions\ **Created:** [July 12, 2008, 6:22pm UTC](https://boards.straightdope.com/t/how-much-reforestation-for-reducing-greenhouse-gases/456251 "2008-07-12T18:22:25Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![drhess](https://avatars.discourse-cdn.com/v4/letter/d/94ad74/32.png) [@drhess](https://boards.straightdope.com/u/drhess)\ **Post date:** [July 12, 2008, 6:22pm UTC](https://boards.straightdope.com/t/how-much-reforestation-for-reducing-greenhouse-gases/456251/1 "2008-07-12T18:22:25Z")
I know some organizations are into the notion of “carbon footprint” reduction and I’m wondering if that notion (or calculation) allows one to figure how much reforestation is equal to how much reduction in greenhouse gas. I’m not sure of the units of measure of either, of course. (And if reforestation programs use greenhouses, is there some kind of pun in there? :smack: ) ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [July 12, 2008, 7:31pm UTC](https://boards.straightdope.com/t/how-much-reforestation-for-reducing-greenhouse-gases/456251/2 "2008-07-12T19:31:55Z")
Parts per million of CO2 seems like a good unit to agree on for that measure. From [Wikipedia](http://en.wikipedia.org/wiki/Carbon_dioxide_in_the_Earth's_atmosphere) > [@](#): > > As of November 2007, the CO2 concentration in Earth’s atmosphere was about 0.0384% by volume, or 384 ppmv. This is 100 ppm (35%) above the 1832 ice core levels of 284 ppm. The National Oceanic and Atmospheric Administration defines the current levels in terms of “a dry mole fraction defined as the number of molecules of carbon dioxide divided by the number of molecules of dry air multiplied by one million (ppm).” Not sure if there’s any kind of “standard forest” though. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [July 12, 2008, 8:07pm UTC](https://boards.straightdope.com/t/how-much-reforestation-for-reducing-greenhouse-gases/456251/3 "2008-07-12T20:07:38Z")
From that same link, 1 ppm of CO2 is 7.5 billion tons of CO2, or about 2 billion tons of carbon. From [A Forest Absorbs More Carbon Dioxide Than Was Predicted](http://query.nytimes.com/gst/fullpage.html?res=9F0CE1DD1239F93BA35755C0A965958260), Dr. Steven C. Wofsy estimated 3500 pounds of carbon absorbed per year per acre, higher than the previous estimates of 2,200 pounds. Splitting the difference, call it about 1.5 tons of carbon per acre per year. That’s after something like a timber harvest in an Oak-Hickory forest (which I’ll take as the “standard forest” :)). If you’re talking about a brand new forest, maybe that changes by some factor, but ignoring that, to absorb 1 ppm of CO2 per year, you’d need 1.3 billion acres of forest, or about 2 million square miles. Remember, we’re currently about 100 ppm above 1832 levels, or about 50 ppm over levels from the 1970s (again,from the Wikipedia link). For [reference](http://www.enchantedlearning.com/usa/states/area.shtml), Alaska is 656,425 square miles. Also, that’s not taking into account how much CO2 is still being added to the atmosphere each year. ---
**Author:** ![drhess](https://avatars.discourse-cdn.com/v4/letter/d/94ad74/32.png) [@drhess](https://boards.straightdope.com/u/drhess)\ **Post date:** [July 12, 2008, 11:11pm UTC](https://boards.straightdope.com/t/how-much-reforestation-for-reducing-greenhouse-gases/456251/4 "2008-07-12T23:11:44Z")
Well, seems like a thousand square miles of reforestation in a place like Haiti could be done in a year or two (granted they are “starter” forests). I assume you cannot quickly get reduction of emissions down low levels very soon, and even if you did, without greenhouse removal strategies, reduction strategies alone won’t fix the problem, will they? How many trees do you need in an acre of forest? [Yes, they get cut down for coal in places like Haiti, but we’ll fix that later and over plant in the meantime 🙂] ---
**Author:** ![ntcrawler](https://avatars.discourse-cdn.com/v4/letter/n/34f0e0/32.png) [@ntcrawler](https://boards.straightdope.com/u/ntcrawler)\ **Post date:** [July 13, 2008, 3:47am UTC](https://boards.straightdope.com/t/how-much-reforestation-for-reducing-greenhouse-gases/456251/5 "2008-07-13T03:47:29Z")
there are other carbon sinks besides forests. the Oceans for instance. They are a significant player too 🙂 Also, according to a recent article in Wired Magazine a tree’s carbon dioxide sucking ability takes a nose dive around 55 years of age, as well as having the potential to release it back into the atmosphere subject to being burned in a forest fire or from decomposing from flooding. According to that article it’s not just how many acres of forest that are planted but that this forest needs to be managed and harvested. Old trees replaced with new trees to maximize their CO2 consumption ability. Link to article [here:](http://www.wired.com/science/planetearth/magazine/16-06/ff_heresies_intro) Section relevant to this topic: proposing a strategy of constnant harvesting and replanting to [keep the tree population young:](http://www.wired.com/science/planetearth/magazine/16-06/ff_heresies_04forests) Turns out the carbon cycle can be pretty complicated according to[this page from the U.S. EPA](http://www.epa.gov/sequestration/local_scale.html) ---
**Author:** ![drhess](https://avatars.discourse-cdn.com/v4/letter/d/94ad74/32.png) [@drhess](https://boards.straightdope.com/u/drhess)\ **Post date:** [July 13, 2008, 5:29am UTC](https://boards.straightdope.com/t/how-much-reforestation-for-reducing-greenhouse-gases/456251/6 "2008-07-13T05:29:26Z")
Interesting. Still, how many tress in an acre? : ) ---
**Author:** ![The\_Flying\_Dutchman](https://avatars.discourse-cdn.com/v4/letter/t/9fc348/32.png) [@The\_Flying\_Dutchman](https://boards.straightdope.com/u/The_Flying_Dutchman)\ **Post date:** [July 13, 2008, 6:03am UTC](https://boards.straightdope.com/t/how-much-reforestation-for-reducing-greenhouse-gases/456251/7 "2008-07-13T06:03:14Z")
Well you have a real problem. Forests can either be a carbon sink or a carbon source in any given year. Canada, with its 6.4 million square miles of boreal forest is predicted to be a carbon source for the nerxt four years. we won’t even use the forest for our carbon counting for Kyoto. This is because of forest fires and insects. ---
**Author:** ![ntcrawler](https://avatars.discourse-cdn.com/v4/letter/n/34f0e0/32.png) [@ntcrawler](https://boards.straightdope.com/u/ntcrawler)\ **Post date:** [July 13, 2008, 6:04am UTC](https://boards.straightdope.com/t/how-much-reforestation-for-reducing-greenhouse-gases/456251/8 "2008-07-13T06:04:06Z")
[QUOTE=drhess] Interesting. Still, how many \*\*tress \*\*in an acre? : ) [/QUOTE] [Tress?](http://www.northcastle.co.uk/guild/art/trance_gemini/tress2.jpg) Depends on how big her waistline is at the time 😃 ---
**Author:** ![drhess](https://avatars.discourse-cdn.com/v4/letter/d/94ad74/32.png) [@drhess](https://boards.straightdope.com/u/drhess)\ **Post date:** [July 15, 2008, 6:35pm UTC](https://boards.straightdope.com/t/how-much-reforestation-for-reducing-greenhouse-gases/456251/9 "2008-07-15T18:35:12Z")
[QUOTE=The Flying Dutchman] Well you have a real problem. Forests can either be a carbon sink or a carbon source in any given year. Canada, with its 6.4 million square miles of boreal forest is predicted to be a carbon source for the nerxt four years. we won’t even use the forest for our carbon counting for Kyoto. This is because of forest fires and insects. [/QUOTE] Insects produce greenhouse gases? In the same way cows do? Or do they smoke alot? ---
**Author:** ![Deeg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/deeg/32/2955_2.png) [@Deeg](https://boards.straightdope.com/u/Deeg)\ **Post date:** [July 15, 2008, 7:49pm UTC](https://boards.straightdope.com/t/how-much-reforestation-for-reducing-greenhouse-gases/456251/10 "2008-07-15T19:49:13Z")
In the long term an old-growth forest is carbon neutral. CO2 is removed from the air and stored internally in the tree (the trunk or leaves, for example). When the tree (or leaf) dies the carbon is slowly released back into the atmosphere as it decays. In very broad terms a forest is a CO2 sink only when it is adding biomass that locks up the CO2. Depending on weather, forest fires, or insects a forest can be gaining or losing biomass in any one year. A newly planted forest will remove some carbon from the atmosphere but if it is eventually harvested it too will be carbon neutral (not counting the energy that is used to harvest the trees.) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 15, 2008, 9:28pm UTC](https://boards.straightdope.com/t/how-much-reforestation-for-reducing-greenhouse-gases/456251/11 "2008-07-15T21:28:49Z")
> [@](#): > > A newly planted forest will remove some carbon from the atmosphere but if it is eventually harvested it too will be carbon neutral (not counting the energy that is used to harvest the trees.) That depends on what happens to the trees after they’re harvested. If they burn, or rot, or get eaten, then it’s carbon neutral. If they get turned into houses or something else that’s going to stick around for a long time, they remain a carbon sink. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [July 15, 2008, 11:39pm UTC](https://boards.straightdope.com/t/how-much-reforestation-for-reducing-greenhouse-gases/456251/12 "2008-07-15T23:39:06Z")
> [@Deeg](#): > > In the long term an old-growth forest is carbon neutral. It may all be a [moot](http://environment.newscientist.com/article/dn14309-world-on-the-verge-of-the-last-great-land-grab.html?DCMP=ILC-tabView&nsref=dn14309) [point](http://news.bbc.co.uk/2/hi/science/nature/7503304.stm).