Monday, December 24, 2012

Real Tree or Artificial Tree?

My family always had real Christmas trees when I was growing up. I've always had real trees as an adult. Living in my own little bubble, it thus came as a shock to me to learn that, of the households that have Christmas trees, over 80% use an artificial tree, according to Nielsen survey results commissioned by the American Christmas Tree Association  (which largely represents sellers of artificial trees). But in a holiday season where the focus is often on whether we are naughty or nice, what choice of tree has greater environmental impact?

There seem to be two main studies often quoted on this subject: "Comparative Life Cycle Assessment (LCA) of Artificial vs. Natural Christmas Tree," published by a Montreal-based consulting firm called ellipsos in February 2009, and "Comparative Life Cycle Assessment of an Artificial Christmas Tree and a Natural Christmas Tree," published in November 2010 by a Boston consulting firm called PE Americas on behalf of the aforementioned American Christmas Tree Association.Both studies assume the artificial tree is manufactured in China and transported to North America.  (If readers know of other recent published studies, please send me a link!)

Here are some of the main messages I take away from these studies:

1) One artificial tree has greater environmental impact than one natural tree. However, an artificial tree can also be re-used over a number of years. Thus, there is some crossover point, if the artificial tree is used for long enough, that its environmental effect is less than an annual series of trees. For example, the ellipsos study finds that an artificial tree would need to be used for 20 years before its greenhouse gas effects would be less than those of an annual series of natural trees. The PE Americas study offers a wide range of scenarios, and summarizes, but here is the situation "for the base case when individual car transport distance for tree purchase is 2.5 miles each way. Because the natural tree provides an environmental benefit in terms of Global Warming Potential when landfilled, and Eutrophication Potential when composted or incinerated, there is no number of years one can keep an artificial tree in order to match the natural tree impacts in these cases. ...  For all other scenarios, the artificial tree has less impact provided it is kept and reused for a minimum between 2 and 9 years, depending upon the environmental indicator chosen."

2) The full analysis needs to look at effects across all the full life-cycle of the tree, whether natural or artificial. This seems to involve the following steps.
  • Under what conditions is the tree manufactured or cultivated, with what use of energy, fertilizer, and logging methods? 
  • By what combination of transportation mechanisms is the finished tree moved to the home? A substantial share of artificial trees are manufactured in China and then shipped to North America.
  • What are the different issues in use of the tree, including use of water and emissions of fumes?
  • What is the end-of-life for the tree? For example, the carbon in a natural tree will be stored for some decades if the tree goes into a landfill, but not if if is composted or incinerated.
3) The full analysis also needs to look at a range of possible effects. For exaaple, the PE America study looked at "global warming potential (carbon footprint), primary energy demand, acidification potential, eutrophication potential, and smog potential." Here's a figure showing 14 categories of analysis from the ellipsos study, with a comparison between natural and artificial trees on a number of dimensions.

The ellipsos study sums up this way: "When aggregating the data in damage categories, the results show that the impacts for human health are approximately equivalent for both trees, that the impact for ecosystem quality are much better for the artificial tree, that the impacts for climate change are much better for the natural tree, and that the impacts for resources are better for the natural tree ..."

4) In the context of many other holiday and everyday activities, the environmental effects of the tree are small. For example,the studies offer some comparisons of the environmental effects of the tree compared with the electricity used to light the tree, the driving by a household to pick up the tree, and even the environmental effect of the tree stand.
For example, in comparing Primary Energy Demand for the tree and the energy demand for lighting the tree. For an artificial tree, the PE Americas study reports: "The electricity consumption during use of 400 incandescent Christmas tree lights during one Christmas season is 55% of the overall Primary Energy Demand impact of the unlit artificial tree studied, assuming the worst‐case scenario that the artificial tree is used only one year. For artificial trees kept 5 and 10 years respectively, the PED for using incandescent lights is 2.8 times and 5.5 times that of the artificial tree life cycle." For a natural tree: "The life cycle Primary Energy Demand impact of the natural tree is 1.5 ‐ 3.5 times less (based on the End‐of‐Life scenario) than the use of 400 incandescent Christmas tree lights during one Christmas season."

In comparing the environmental effects of driving with those of the tree, ellipsos writes: "Due to the uncertainties of CO2 sequestration and distance between the point of purchase of the trees and the customer’s house, the environmental impacts of the natural tree can become worse. For instance, customers who travel over 16 km from their house to the store (instead of 5 km) to buy a natural tree would be better off with an artificial tree. ... [C]arpooling or biking to work only one to three weeks per year would offset the carbon emissions from both types of Christmas trees.

The PE Americas report strikes a similar theme: Initially, global warming potential (GWP) for the landfilled natural tree is negative, in other words the life cycle of a landfilled natural tree that is a GWP sink. Therefore, the more natural trees purchased, the greater the environmental global warming benefit (the more negative GWP becomes). However, with increased transport to pick up the natural tree, the overall landfilled natural tree life cycled becomes less negative. When car transport becomes greater than 5 miles (one‐way), the overall life cycle of the natural tree is no longer negative, and there is a positive GWP contribution." 

Even the tree stand for a natural tree has an environmental cost that can be considered in the same breath with the costs of a natural tree. PE Americas: "The tree stand is a significant contributor to the overall impact of the natural tree life cycle with impacts ranging from 3% to 41% depending on the impact category and End‐of‐Life disposal option."

I would add that the environment effect of the ornaments on the trees may be as large or greater than the effect of the tree itself. Data from the U.S. Census Bureau shows that America imported $1 billion in Christmas tree ornaments from China (the leading supplier) between January to September 2012, but only $140 million worth of artificial Christmas trees. Thus, spending on ornaments is something like six times as high as spending on trees. The choice of what kind of lights on the tree, or whether to drape the house and front yard with lights, is a more momentous environmental decision than the tree itself.

Of course, these kinds of comparisons don't even try to compare the environmental cost of the tree with the cost of the presents under the tree, or the long-distance travel to attend a family gathering. Thus,  the PE Americas study concludes: "Consumers who wish to celebrate the holidays with a Christmas tree should do so knowing that the overall environmental impacts of both natural and artificial trees are extremely small when compared to other daily activities such as driving a car. Neither natural nor artificial Christmas tree purchases constitute a significant environmental impact within most American lifestyles." Similarly, ellipsos writes: "Although the dilemma between the natural and artificial Christmas trees will continue to surface every year before Christmas, it is now clear from this LCA study that, regardless of the chosen type of tree, the impacts on the environment are negligible compared to other activities, such as car use."

Certainly, celebrations at holidays and big events can sometimes be exorbitant and over the top. But the use of a Christmas tree, and the choice between a natural tree or an artificial tree, is a small-scale luxury. If the environmental issue is bothering you, even knowing these facts, make a resolution to use your artificial tree for a few more years, rather than replacing it, or to save some energy in January by driving less or being more vigilant about turning off unneeded lights. Gathering around the tree should be one less reason for moralizing around the holidays, not one more. So celebrate with good cheer and generous moderation.