Carbon credits. At this point, if you haven’t heard the name, you might well be living in a culture that doesn’t use fossil fuels. But the basic idea is that if you’re creating CO2 from burning fossil fuels, you can do “something” to compensate by buying carbon credits. These might go to the planting of trees or some other activity that reduces CO2 production elsewhere. You can argue over whether this makes a difference to our long-term future, or not, but that’s really outside the scope of what I want to write about here. Thinking in terms of my back yard, what can I do to first reduce, and subsequently offset my CO2 production?
The first step I took (starting in 2010) was planting my own trees. Estimates are that each tree may capture 2.5-5.5lbs of CO2 per year depending on age. Considering how quickly I can plant trees, though, this doesn’t amount to much. The key, though, is that the trees I’m planting are part of a coppice grove, which should supply me with firewood. More on coppice at the end, if you’re interested.
The next step I’ve taken is to stop using natural gas. When my home was built, the installed heat and hot water source was a natural gas boiler. I started heating primarily with wood in 2012; although there are some deadfalls on the property and one or two trees that I’ve had to take down for other reasons, most of this wood was purchased from local suppliers. (Unless you want to pay for the energy of kiln-drying, you must buy your firewood locally.) Then, in 2013, I was able to eliminate the boiler by having a solar “domestic hot water” system installed. The only remaining gas appliance is my cookstove, where I decided that the embodied energy (about 1325kWh equivalent) was more than the CO2 involved in keeping it running off of propane. (So far it’s looking like 10 years worth of use will be about equivalent to the replacement energy – but then I’m still on my first 40lb propane tank so I might be underestimating the years.) Also, out in the future, I may be able to use a biogas digester to run the stove. And yes, I need a backup for the solar DHW and for the wood stove… but those are both electric, running off my grid-tied solar PV array, which is backed up by buying more wind credits than I actually use.
Of course, all of this is only part of my CO2 use, because I still drive a car, and because my work requires me to travel overseas periodically, which leads to air travel. In the most recent year, my Prius accounted for 31% of my CO2 production, and the flights for 67%, so I’ve reduced the home energy to only 2% of my total, much lower than typical use. So now we’re back to the question of carbon credits, and how I can choose carbon credits that are local. That has an easy answer: the Finger Lakes Climate Fund. If I offset my carbon use here, it turns into grants for local homeowners to improve the energy efficiency of their own homes.
So in summary:
Before/After CO2
| Past | Present | Future | |
|---|---|---|---|
| Heating | Natural gas | Locally sourced wood Electric backup | On site coppice wood |
| Hot water | Natural gas | Solar DHW Electric backup | (same) |
| Cooking | Natural gas | Propane cookstove | Biogas cookstove? |
| Home energy1 | 50% | 1% | TBD |
| Automobile energy1 | 80% | 48% | TBD |
| Airplane energy1 | ? | 98% | Lower? |
1 As a percentage of single family detached green home/green car, conventional suburban development, per the EPA. Note that the transport numbers are cumulative: I used as many BTU flying as most households do for their entire annual transportation. Not good, but all of the flying represented was job-related.
I said I’d write a little more about coppice for those who are interested. The coppice grove has been in use in Europe (particularly the UK) for so long that they are considered unique ecosystems. The principle is simple – there are many trees that will regrow new shoots from cut stumps; the regrowth is more vigorous because the established root system can supply nutrients much more effectively, and the harvesting and regrowth can be repeated over and over on a relatively short cycle. (Some trees, or some ecosystems, will work better with “pollarding”, where the cutting happens far above the ground.) Estimates for coppice productivity range from 1 cord/acre/year to as high as 5 cords/acre/year!
Since I’m burning about 1 cord/year, we allocated 2 acres for coppice but I started out by planting only 1/2 acre. One of the good (and bad) things about initially establishing a coppice is that you want to plant only a fraction of the trees each year – less work, but you have to wait a long time (10-15 years?) before your first plantings are of harvestable size, and you know what your yields will be. In any case, I’ll be buying from the local wood suppliers for a while longer still. However, because I’m planting a more esoteric (if historically suggested) coppice, I will get some productivity sooner.
Some of the preferred species for firewood coppice are ash, beeches, poplar, some oaks, and black or honey locust. But in the old days, coppice was used for a lot more than firewood: fence posts, fencing withies (willow), tool handles (and going back to pre-iron age, even tool blades including plowshares!), furniture… So I’ve elected to plant a coppice that includes a variety of species, starting with quite a bit of apple.
Apple has the following advantages: coppices very well (even past the first 15-20 years); can be grown from seed readily (so I don’t need to buy expensive orchard trees); excellent firewood; excellent wood for smoking meats; excellent wood for turnery (making things on a lathe) and other woodworking; and, oh yeah, it produces food. Now when you grow an apple from seed of a good eating apple, you know something about the genetics – at least one of the parents tasted good – but you really don’t know if you’re going to get something of quality. On the other hand, if you plant fifty of them, chances are that you’ll get something out there that’s good for eating, and a bunch of things that are decent for making cider. Since we have orchard spaces elsewhere, there’s no reason at all why we can’t graft out branches from any apples that happen to be delicious.
I’m including some other trees in the coppice rotation as well; the variety leads to a more diverse ecosystem and different trees will have different uses. Some “thornless” honey-locust (Gleditsia triacanthos var. inermis, acquired cheaply from the local soil conservation district), some Kentucky coffee tree (Gymnocladus dioicus – doesn’t coppice! – but I got it for free from a friend, and it does produce a coffee substitute and is good firewood), and planned for this year, swamp white oak (Quercus bicolor, which does coppice and which does well in poorly drained soils).