Is a natural or an artificial Christmas tree the more environmentally-friendly option?  The answer may depend on the consumer’s circumstances.

As environmental issues go, this is admittedly a small one.  But if we can’t get right small issues like this, what hope is there for making the right choices on bigger and more complex issues?

Our tree, Christmas 2010 (and 2011 and 2012, and probably many years to come)

A widely-quoted and very detailed study by Ellipsos (1), a Canadian consulting firm, compared locally-grown natural trees and artificial trees imported from China, applying the methodology of Life Cycle Assessment in accordance with the relevant international standards (ISO’s 14040 & 14044).  Environmental impacts were assessed in detail for production, transport, use and disposal, with the results grouped under four damage categories: human health, ecosystem quality, climate change and resources.  The central results suggested that natural trees had lower climate change and resource depletion impacts, while artificial trees had lower ecosystem impacts.  Human health impacts were very similar (2).

However, these results were shown, in the study’s sensitivity analysis, to depend heavily on assumptions made.  Two of the most important relate to the life of the artificial tree, taken to be 6 years, and the journey made by the consumer to buy the tree (5 kilometres each way by car).  A general limitation, in accordance with advice in ISO 14044 (3), is that no weightings or valuations were applied to the damage categories to obtain a single overall measure of impact for each type of tree (4).  Therefore, although the study states that the natural tree is a better option, this conclusion is not clearly supported by its results.

Here are my conclusions, based on the Ellipsos study and other sources:

Guideline 1
If you have kept an artificial tree from last year, then it would be advisable to assess the degree of risk it represents in respect of lead toxicity, having regard to age, physical condition and any information provided.  Depending on your assessment, you might decide it can be used as before, or can be used with precautions, or is best disposed of.  Precautions might include keeping young children away, washing hands after contact, and not placing gifts beneath the tree.
Explanation:  A study by Levin et al of lead exposure in US children (5) identified artificial trees as a possible source of harmful exposure to lead, used as a stabilizer in PVC, referring to research by Maas et al (6).  This research concluded that, although there was no significant exposure risk from the average artificial tree, a substantial risk to young children was possible in a worst-case scenario.  The relevance of a tree’s age is twofold: older trees are more likely to begin to disintegrate and release lead dust, and newer trees are more likely to be lead-free (with tin as a stabilizer instead) (7).

Guideline 2
If you have an artificial Christmas tree which you assess as reusable without unacceptable lead risk, then re-using it is the environmentally-friendly choice.  
Explanation: There are no significant environmental costs of using the tree again.  The environmental costs at the production and transport stages have already been incurred and are therefore irrelevant to your current decision.

Guideline 3
If you need to buy a tree, but expect that your circumstances will change within 2 or 3 years so that you would not keep an artificial tree longer than that, then a natural tree is probably the environmentally-friendly choice.
Explanation: The environmental impacts of an artificial tree in production, including consumption of resources such as iron and carbon emissions from the energy used, are much higher than those of a natural tree (8).  Because of this, the overall environmental impacts of an artificial tree per year of use will be higher than those of a natural tree unless the artificial tree is used for many years.

Guideline 4
If you need to buy a tree, and expect that you would keep using an artificial tree for many years, and if you would have to make a long car journey for the sole purpose of buying a tree of either kind, then an artificial tree is probably the environmentally-friendly choice.
Explanation:  A 16 kilometre car journey to buy a natural tree that will be used once and then disposed of makes a large contribution to the life-cycle environmental impact of that tree in respect of both climate change (carbon emissions) and resource consumption (petrol).  According to the Ellipsos study, the impacts of a natural tree are then worse than those of an artificial tree with a 6 year life in respect of human health and ecosystem quality, and about the same for climate change and resources (9).

Guideline 5
If you expect that you would keep using an artificial tree for many years, and could buy either a natural or an artificial tree without making a long car journey, then choose the kind of tree you prefer or find more convenient or is cheaper!
Explanation:  I can find no convincing environmental reason to prefer either kind of tree in these circumstances.  There does not seem, for example, to be sufficiently reliable information on rates of carbon sequestration by young trees.  Christmas trees are typically harvested at 12 years or less, so inferences cannot reliably be drawn from studies of mature forests.  For its sensitivity analysis in this respect, the Ellipsos study considers a range of sequestration rates of CO2 per hectare per year from 3 tons to minus 0.5 tons (10).

And finally … bear in mind that this is a very small issue.  As Ellipsos point out, regardless of the type of tree chosen, its environmental impacts are negligible compared to, say, regular car use (11).

Addendum (12 Dec 2012):  Since posting the above I realise that it is also possible to rent a natural tree, which after Christmas the supplier would take away, replant, grow for another year, and rent out again.  Where this can be done without the supplier having to make long journeys for individual trees, it would probably also be an environmentally-friendly option.

Notes & References

1.  The Ellipsos Study:  Couillard S, Bage G & Trudel J-S (2009) Comparative Life Cycle Assessment ofArtificial v Natural Christmas Tree                                                                    http://www.ellipsos.ca/site_files/File/Christmas%20Tree%20LCA%20-%20ellipsos.pdf

2.  Ellipsos as above, p 36

3. Wikipedia  Life Cycle Assessment      http://en.wikipedia.org/wiki/Life_cycle_assessment#Life_cycle_impact_assessment

4. Ellipsos as above, 2nd review letter 15/12/2008 pt 2 (appended to main report)

5.  Levin R et al (2008) Lead Exposures in US Children, 2008: Implications for Prevention Environmental Health Perspectives Oct 2008  pp 1285-1293 (see section on PVC) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2569084/

6.  Maas R P, Patch S C & Pandolfo TJ (2004) Artificial Christmas Trees: How Real are the Lead Exposure Risks? Journal of Environmental Health Dec 2004 (Abstract) http://www.ncbi.nlm.nih.gov/pubmed/15628192

7.  Ellipsos as above, p 17

8.  This can be inferred from Ellipsos, pp 27 & 36

9.  Ellipsos as above, p 41

10.  Ellipsos as above, p 43

11. Ellipsos as above, p 8