Your greenhouse gases: simple math

I have good news and bad news. Bad news first.

Climate change is caused predominantly — if not exclusively — by human activity. Alas, I’m human, so my bad. At least in part.

The good news? We humans can do something about it. We can shrink our personal carbon footprints, and if we all do it then the collective difference will be significant. But how do we measure our carbon footprint? And how do we know if we are shrinking it?

On one level, it’s easy. Most of us make our direct contributions to climate change by burning fossil fuels, mainly natural gas and gasoline. It’s easy to track how much we’re using because we get a receipt at the gas pump and a monthly bill from Avista. From there the math is simple: one gallon of gasoline produces 8.8 kilograms of greenhouse gases (GHG); one therm of natural gas produces 5.3 kilograms of GHG. Multiply out, add the two together, and you have your direct GHG emissions.

Yes, using electricity also results in GHG emissions, albeit indirectly. But that’s more complicated so we’ll treat it separately.

Last year I decided to track and quantify our direct household GHG emissions, aiming at substantial reductions. I first estimated our prior yearly GHG emissions, calculating from annual mileage on our cars and the chart shown on our Avista bill. I came up with a figure of 4,184 kilograms (kg). For the 12 months starting July 1, 2017, I targeted a reduction of 10 percent, or a total of 3,766 kg. I created a spreadsheet and started tracking, month by month.

Here I should note that our home has a hybrid heat pump HVAC system. It operates as a heat pump down to 35 degrees, and then switches to gas. Our kitchen range and water heater are gas.

Also, in May 2017 we leased a new plug-in hybrid electric vehicle (PHEV). It will max out at 53 miles on electricity before switching to gasoline, continuing at around 38 mpg on the highway. Our other vehicle is a 2006 compact SUV, usually driven only when the PHEV is away on a longer trip or when we need the extra space or all-wheel drive.

So, how did we do? Modestly, I surprised myself. My target was direct GHG emissions of 3,766 kg. The actual tracked total was … 3,761!

I was a bit concerned that we would go over as we took several long road trips I had not anticipated, putting over 9,000 miles on the PHEV and almost 2,000 on the SUV. So despite driving on electricity almost everywhere in the valley, we did consume 198 gallons of gasoline, accounting for 1,742 kg of our total emissions. How does that compare to the U.S. average? Quite well. The average U.S. driver consumes 656 gallons a year; a two-driver household like ours would total over 1,300 gallons.

What about natural gas? It was a relatively mild winter, with few days below freezing, so most heating was with our electric heat pump. We used 380 therms and thus emitted 2,014 kg of GHG. Quick Google research reveals a U.S. residential average of 613 therms per year. Yes, we’re doing better than most — but we have a heat pump and we don’t live in Minnesota.

I also tracked our electricity, though there’s no precise way to convert a kilowatt-hour (kWh) to GHG emissions. That’s because GHG amounts produced in generating electricity will vary seasonally, and even hour by hour, depending on the mix of fossil fuel and renewable sources on the regional grid. However, if we take the (very good) Oregon average of 0.18 kg per kWh, our total of 8,892 kWh comes out to 1,601 kg of GHG. Not bad, considering that includes about 2,500 miles of vehicle travel. The U.S. household average is supposedly 10,766 kWh annually.

So, that’s year 1. For year 2, we’re aiming at 3,390 kg of direct emissions — another 10 percent cut — while reducing electricity consumption by 5 percent.

If you’re a human who believes we’re all responsible for climate change, please join us. The math is simple, really.

Bruce Borgerson lives in Ashland.

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