Frequently Asked Questions
What is a carbon footprint?
A carbon footprint is a quantitative measure describing the amount of greenhouse gas (GHG) emissions that result from an individual’s activities.
Most everything we do has some level of emissions associated with it,
but for most people, the majority of emissions result from energy use,
such as home and transportation.
Why is measuring my carbon footprint important?
Individual actions contribute to the problem and to the solution. If everyone were to do their part, we might slow or even stop the impacts of climate change. It starts with you. By measuring your carbon footprint, you can gain insight into the actions that can lead to substantial reductions in emissions for you.
How is a carbon footprint calculated?
Estimating direct emissions from household energy use and transportation is fairly straight forward. Information about household energy use is available on your PSE bill, and once natural gas (listed as `therms`) and electricity (listed as `kWh`) usage is known, these can be converted to carbon emission numbers. The conversion for electrical footprint is somewhat location dependent, as it depends on what combination of energy sources are used to create the electricity. For Mercer Island, its approximately 0.33 lbs CO2 per kWh. Natural gas is less variable and is approximately 11.7 lbs C02 per therm.
Similarly, for personal auto usage, information about gallons of gasoline (19.6 lbs CO2 per gallon) or diesel (22.4 lbs CO2 per gallon) used can be converted to carbon emission numbers.
Airline travel is a little trickier, but works off of trip mileage.
Pounds, tons, or parts per million?
Personal emissions are typically calculated in units of either pounds (lbs) or metric tons (mton). A metric ton is roughly 2204 pounds. Atmospheric CO2 is typically measured in terms of parts per million (ppm).
Direct conversion between personal emissions and atmospheric CO2 is a little challenging particularly given the various naturally occuring sources and sinks of carbon.
How much uncertainty is there in the science behind climate change?
Climate science is not perfect. But it seems much more of the debate about whether climate change is `real` is political and not scientific. Scientists understand a lot, and while sure there are holes and uncertainties in our understanding of climate forcings, this doesn't diminish the overwhelming body of evidence. Its much more an incomplete jigsaw puzzle than a house of cards.
A few websites that provide detail about the science behind climate change include Climate Progress and Real Climate.
What is the right reduction “goal”? What is a realistic timeframe for reduction?
Because of some uncertainty about how climate change is going to impact things, there is some debate about what the right overall goal is. The pre-industrial atmospheric CO2 was something near 280 ppm and had been pretty stable for 10,000 years or so. As of March 2010, we’re at just over 390 ppm. James Hansen at NASA and others (350.org) have argued that we should attempt to stabilize the atmosphere at something below 350 ppm to avoid catastrophic climate change. This requires a reduction from the current level.
Using that as a guide, if as a world we could get to carbon neutrality (see below), we could then let the natural “sinks” work to bring atmospheric CO2 back down.
Regarding timeframe, achieving carbon neutrality is not going to be easy, and apart from using offsets, is probably not going to happen quickly. It will also depend on individual circumstances. Maybe a 10 year plan is appropriate to really minimizing your carbon as much as possible, and then use offsets for the rest.
What is carbon neutrality?
Carbon neutrality describes a lifestyle that theoretically has NO associated carbon emissions. This is difficult to achieve on its own, however with carbon offsets (see below) this might be possible.
What are carbon offsets?
Carbon offsets allow one to mitigate a set amount of carbon through investments in clean energy and carbon capture projects. Using offsets then theoretically allow the amount of carbon emissions mitigated to be subtracted from individual emissions. For example, if I pay to develop a project that reduces a set number of tons of GHG emissions, then this could count against my personal carbon footprint. A number of vendors sell carbon offsets, usually for something on the order of $20/mton.
However, it should be noted there is some debate about the effectiveness of carbon offsets, such as the additionality argument – how can one know that the given project wouldn’t have otherwise occurred. If it would have, then credit probably shouldn’t be given for it.
Two points about carbon offsets are worth making. First, using offsets without also making reductions in personal emissions will probably be ineffective toward the cause. A better approach is to reduce emissions as much as possible, and then use offsets for the rest. Second, before investing in carbon offsets, do your research.
What are direct versus indirect emissions?
In one definition, direct emissions are those that are completely controllable – house energy, transportation, etc., whereas indirect emissions are those that result from purchase of food, etc.
If I’m using green power, should that count as part of my footprint?
In the simplest view, green power might be considered in a similar manner to an offset. When you purchase green power through PSE, the electrons flowing to your house aren't necessarily from renewable sources, but instead you are investing in development of more green power. Therefore, while green power helps, you might also consider how you can also reduce your electricity consumption.
Have other questions?
E-mail us! bruce@ecoshift.org. We're happy to try to answer questions about carbon emissions or climate change.