Paula Morgenstern and Jenny Love, UCL Energy Institute
Sometimes, doing a PhD gets to you – and in such situations a good argument can work wonders. At last week’s lowest point, Paula and Jenny practised stress-release by arguing whether real or artificial Christmas trees are better for the environment. While Jenny thought there was no way that natural trees could be more sustainable, Paula was convinced of their superior qualities.
Jenny: “With an artificial Christmas tree, you don’t have to buy a new one each year.”
Paula: “True, but a real Christmas tree captures carbon during growth.”
Jenny: “Fair enough, but artificial trees are mass-produced and therefore efficient.”
Paula: “Yes, but what happens at the end of their lives? A real tree in a house with a fireplace can give warmth and cosiness until weeks after Christmas.”
To base the argument on a more scientific basis, we chose to borrow from an approach called ‘Life Cycle Analysis’ (mentioned on this blog before: https://energyandlife.wordpress.com/2012/03/26/i-feel-like-chicken-tonight/ ). LCA’s central idea is the consideration of all stages in the existence of a product – from its production to its disposal – and work out how much impact each stage has on whatever you care about – eg. climate change, pollution, resources depletion. We, being energy researchers, will focus on impact on climate change.
Now, because we’re supposed to be doing our PhDs, we didn’t do the calculations ourselves, but have summarised the brilliant and highly detailed piece of work by the Canadian consultancy Ellipsos ( http://www.ellipsos.ca/site_files/File/Christmas%20Tree%20LCA%20-%20ellipsos.pdf ) to form our arguments.
ARTIFICIAL CHRISTMAS TREE
There are four main stages to consider here:
1) Production: How do you manufacture a Christmas tree? Mostly by making plastic (PVC), by heating oil-based products in various ways and creating nasty chemical by-products you have to dispose of in a safe way.That’s the needles covered. Then you have to make or reuse some steel, for the branches and the stand. This requires raw materials and a lot of electricity. Then you put it in a cardboard box, ironically created from chopping down a tree.
2) Distribution: Most manufactured goods we buy in the UK are shipped here from China. To give you a rough idea of the impact of this, we calculated that each Christmas tree shipped over causes CO2 emissions of about 12kg, which is the same as you driving an average car 70km.
3) Taking it home: The real advantages of the fake tree is that once it’s home, it doesn’t use any resources, and can be kept for a number of years. The latter is an important factor: the study says that you have to keep your fake tree for 20 years for it to cause smaller global warming impact than a real one.
The study estimates that the most significant bit of the artificial tree’s impact is its manufacturing, followed by its shipping, followed by its journey from the shop to the customer’s house.
1) Early growth in a tree nursery: This takes about 4 years and is by now something many UK nurseries have recognised as profitable business opportunity. Both the climate impacts and the environmental impacts of this life phase of the Christmas tree are negligible – meanwhile, the growing trees might give pleasure to nursery passers-by.
2) Continued growth in a field: As soon as the Christmas trees are big enough, they are transferred from the nursery into the field. There, they continue growing for another 11 years until they reach a sellable height of approximately 7 feet. During this time, every tree captures a significant amount of carbon (A field of trees captures 2 tonnes CO2/hectare/yr.).
3) Tree sale and transport to someone’s home: In this phase, much of the carbon credits from tree growth are consumed again. If someone, for example, travels 5km by car to his nearest tree seller, the 10km of the return journey amount to nearly half of the carbon previously captured in the tree. Further travel could reverse the effect altogether.
4) Production of the tree stand and its transport: Most people use steel stands for their Christmas trees which are predominately produced in China. The amount of material needed and the transport of the completed stand have the strongest environmental impact during this phase.
5) Christmas holidays: During the holidays and as opposed to an artificial Christmas tree, a natural tree needs some care. You may talk to it if you wish, but firstly it needs some water. The environmental impacts of watering and hovering fallen needles however are negligible.
6) After the Christmas holidays: Christmas trees are normally either recycled or burned in fireplaces. The overall environmental impacts of recycling price it as the more favourable of the two options, but if the heat from burning the Christmas tree replaces oil or natural gas otherwise used to keep your house warm, climate change impacts are lower here.
SO, HOW GREEN IS YOUR CHRSTMAS TREE THIS YEAR? Comparing the LCA results for both trees shows that natural Christmas trees are better for our climate than plastic ones. So if it is climate change you care about, then a real tree is definitely the way to go…
But what about other impacts except climate change? One aim of life cycle analysis is to tell us not only about climate change but also about the use of natural resources and other impacts on the quality of our eco-system.
Here, natural Christmas trees still beat artificial ones in terms of material consumption, but land use and fertilizers mean that negative impacts on the ecosystem are bigger for real than for artificial trees.