During the darkest days of December, many Americans light up their homes with menorahs, Christmas trees, and perhaps lawn decorations, too. It is good for the soul, but what about the planet?
Christmas trees are mostly lit with LEDs these days, for economy and safety. (All the watts in a light eventually turn into heat, so lower wattage means less chance of ignition.) LED mini-lights are less than one watt per bulb, and an indoor tree might get by on 23 watts. If it burns for 12 hours a day, for 15 days, that comes to 4,000 watt-hours. Any trees strung with incandescent lights, which are barely sold at retail any longer, would use nearly ten times as much.
For the United States, the average carbon footprint of a kilowatt-hour is about .82 pounds. So, all told, the indoor tree would have a carbon footprint of about 3.3 pounds. (Omitting, of course, that once the tree is dead, the carbon that it sequestered in its wood will likely find its way into the atmosphere.) The National Christmas Tree Association predicts sales of 25 to 30 million trees, but this does not count artificial trees that have lights, or the live trees in peoples’ front yards that are draped with lights. Nor does it include plastic Santas and Rudolphs with illuminated noses. Forbes estimated two years ago that holiday lights consume about 35 billion kilowatt-hours, but precision is impossible.
As for Menorahs, estimates vary, but a Hanukkah candle (which is bigger than a candle for a birthday cake, but a lot smaller than a candle in a typical candelabra) emits about 7 grams of carbon dioxide, over however long it takes to burn, and the box that lasts eight days has 44 candles. There’s one candle that’s used to light the others, plus one on the first night, two on the second, three on the third, etc, until you reach 8. That’s 308 grams, about .68 pounds. Across the country, millions are burned.
College dorms, nursing homes, and apartment house lobbies typically use electric menorahs. The one in my lobby, for example, uses 3-watt incandescents, and they burn around the clock. Two burn for eight days, three for seven days, four for six days, and so on, giving a total of about 3,200 watt-hours. That puts the incandescent menorah at about 2.6 pounds of carbon dioxide. An LED model would cut the load to about 400 watt-hours, with .33 pounds of carbon dioxide.
Counting the menorahs that show up in drugstore gift displays next to the 3-foot-tall Christmas elves imported from China, the number is probably in the low millions.
Individually, these numbers are quite small. Even a lit Christmas tree has a smaller footprint than driving a gasoline car five miles. But the impact is not zero, and there are easy ways to make it smaller by cleaning up our electricity mix.
For example, using the biggest footprint here, the one for the Christmas tree that is lit twelve hours a day for fifteen days, we can calculate the carbon dioxide impact of electricity from various sources, using numbers from UN Intergovernmental Panel on Climate Change. The figures used here are for the median estimates gathered in the IPCC study.
If the electric grid relies on coal, the carbon dioxide footprint of that tree is 7.2 pounds. For combined cycle natural gas, it's 4.3 pounds. Getting into renewables, hydropower could shrink the footprint to 2.1 pounds; solar photovoltaic (not counting losses from batteries, which are required for after-dark uses) to .42 pounds; and onshore wind to .10 grams. Nuclear, the only source that could be scaled up enough to realistically meet the country’s festive electric needs clocks in at .11 pounds.
If the Forbes estimate of 35 billion kilowatt-hours is roughly correct, that electricity coming from coal would account for about 29 billion pounds. From nuclear, less than a billion pounds.
Fixing pollution from holiday lights won’t make a lot of difference to the climate, but the numbers do illustrate how the benefits of cleaner electricity sources like nuclear add up.