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In this era of growing concerns about global warming, the tradition of chopping down millions of trees each year only to discard them a few weeks later, might strike some people as bizarre.

But does it actually harm the environment? By the time the tree is discarded, have we added to or removed carbon emissions?

There are many subjective media articles on the subject, but I'm looking for something more concrete based on confirmed numbers. Ideally I would like to calculate a carbon footprint (+ / -) per christmas tree, based on averages.

Possible factors which increase carbon emissions:

  • A felled tree no longer takes part in photosynthesis.
  • Carbon emitted during the manufacture and transport of agricultural equipment and consumables (e.g. pesticides and fertilizers).
  • Carbon emitted during transport of the tree to the customer.
  • Methods of discarding used trees such as burning.

Possible factors which decrease or are neutral for carbon emissions:

  • Trees are constantly replanted, and those trees might not exist otherwise.
  • Recyling used trees (e.g. composting).
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    I can't find it now but I read an article about this probably about a year ago, which cited figures. The conclusion they reached was that pot-grown trees are best, if you keep them for several years -- slightly more transport emissions per tree, fewer trees per house. – Chris H Dec 22 '15 at 10:09
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To qualify my answer I have ended up here following research into the new agreement made today in Paris regarding climate change (COP21). There appears to be a consensus that one of the most important ways of mitigating greenhouse gas emissions is to plant trees and then burn them in carbon capture facilities, generating energy but trapping carbon. (I have not read the whole document yet.)

Key to this reasoning are the following assumptions;

  1. The energy consumed in the growing of the seedling/sapling (nursing), planting, transport, etc., must be carbon neutral or have a low and known figure.
  2. The plant should naturally have a low greenhouse gas footprint. For example - broad leaved deciduous trees may have a higher emission of gasses if they drop leaves every year (which rot) and grow slowly.
  3. Lastly, the method and timing of using the timber created is very important. If you burn it on a fire, then there is no benefit and possibly a negative effect.

The best option is to make things from it – tables, chairs, cutting boards, etc. – then at the end of the life of those products, make chipboard and eventually burn the chipboard in a pyrolysis plant or high temperature incinerator with a carbon capture system (this last part is important). Such systems are very rare and mostly experimental at the time of writing.

To try and answer you question succinctly;

It is likely that Christmas trees have a negative impact on climate, because

  • almost invariably there is a huge amount of diesel used in the vehicles that plant, process and deliver the trees, and
  • the trees are ultimately either left to rot which releases greenhouse gases (some more potent than CO2), or they are burned, in which case they release all the carbon they captured over the last 3-4 years without mitigating any of the carbon emitted from fossil fuels in their production.

Hope that helps.

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    Thanks for the answer. Ideally I'm looking to quantify the various factors so we can calculate a carbon footprint for buying a christmas tree. On your last point, it's important to take into account the carbon that is stored during the lifetime of the tree. It's not an issue that the carbon is released during disposal - after all, that is the case for all trees in the wild. If a christmas tree is planted on land that wouldn't have otherwise had a carbon storing plant (or a less efficient one) then there is a carbon benefit while it is alive. – JBentley Dec 13 '15 at 21:12
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    @JBentley from what I've seen christmas tree farms are not net carbon stores, they either coppice, or they plough or burn before regrowing. Temporarily storing some carbon over a 2-5 year lifespan isn't useful in terms of carbon emissions, any more than many of a CCS schemes where the design life is under a century. – Móż Dec 14 '15 at 1:17
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Mσᶎ is correct; you cannot include the embedded carbon of the tree itself because of it's short time in captured state. unless you take the tree's back from customers and then dispose of them in a very specific way.

We will assume you cannot or would not do that; therefore all the factors are negative and contribute towards a carbon footprint. This includes everything from the growing of the seedling through to the delivery to the point of sale. The analysis is a complex one and there are many consultants who can do it for you. You would need the cooperation of many suppliers too, though some will already have this information available.

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