Inside a Carbon Calculator

Today’s Guest Blogger, Lisa Moore, is a scientist in the Climate and Air Program.

There’s a new site on Yahoo! that can calculate how much your carbon dioxide (CO2) emissions go down when you try their energy saving tips. It’s fun to use, and I especially appreciate the snazzy interactive features because I know how hard people worked to build it. My colleagues and I provided the Yahoo! design team with the data they use in their calculations.

I hope you’ll visit the site to see how simple changes in your house and car can save energy and lower emissions. But first, let me take you behind the scenes to the complicated world of carbon calculation.

When Yahoo! turned to us for help in calculating the environmental impact of different actions, they gave us an impressive list of things to quantify. I don’t know if they expected the equally long list of questions they got in reply! Here are just a few examples of the questions you need to ask when building a carbon calculator:

  • Which emissions do you count? For the Yahoo! calculator, we focused on emissions from home energy use, personal driving, and commercial aviation. We could make solid estimates of average emissions from these activities, and there are easy steps individuals can take to reduce those emissions. These three activities account for 9.4 tons of CO2 per person per year, which is about half of the total CO2 emissions per person in the U.S.
  • How do you count those emissions? Greenhouse gas emissions are often higher when you consider gases other than CO2, but non-CO2 emissions can be difficult to calculate. Many carbon calculators ignore all non-CO2 emissions. The Yahoo! calculator includes non-CO2 gases for flying and dietary choices.
  • How much information from the user? The more information I have, the better job I can do calculating your baseline emissions and your savings. What’s your current average annual electricity consumption? What state do you live in? How long do you keep each of your light bulbs on every day? What make and model are your appliances? Obviously that approach can get ridiculously cumbersome to users. So instead we often use national averages.
  • Do you include regional differences? Some factors, such as the amount of CO2 emitted per kilowatt-hour of electricity, vary enormously from state to state. The national average emissions rate is 1.34 pounds of CO2 per kWh. But in North Dakota it’s 2.24, and in Vermont it’s a clean 0.03! We accounted for these differences in our calculators on; Yahoo! uses the national average.

Designing a tool like this involves a lot of interesting discussions and decisions (and headaches from boring federal reports like the EPA’s emissions inventory [PDF]), but the end result is very useful. Americans have a huge impact on global warming, there are many things we can do to make a difference.

So click around the site, get a sense of which changes will have the biggest impact, and pledge to do something. Did an item on the list surprise you? What have you already done? What do you plan to do next? I look forward to the discussion.

This entry was posted in News. Bookmark the permalink. Both comments and trackbacks are currently closed.


  1. Energy Guy
    Posted May 17, 2007 at 3:35 pm | Permalink

    First, I think the ste looks really good and is well designed. But, I have a few comments. I’ll try to hit some highlights:

    1) There appear to be some bugs as I found CO2 savings of negative 0.01 tons for many of the energy items, including replace windows, shut down computers, turn off lights clean a/c filter.

    2) The item buy a hybrid or 10% more efficient car is only counting impact of a 10% mpg improvement, way too low for hybrid’s value.

    3) Some energy savings figures are questionable or too non-specific. Example: checking whether a home is well insulated saves no energy. Adding insulation to uninsulated walls does save energy — more than you estimate. Attic and wall insulation should be separate and savings should be based on adding insulation.

    4) You miss potential high impact measures: blower-door guided air sealing (maybe 5 MMBtu) duct sealing in hot climates (maybe 15% A/C load)

    5) Savings too low for thermostat 2 degree change, air dry clothes, maybe replace fridge (depends on age)

    6) Savings too high for showerheads (existing heads use about 3 gpm, not 5) solar DHW especially if gas (unless you assume 100% DHW load is solar).

    BTW, average gas heat usage was 634 ccf/yr. in 2005 (AGA) and is about 800 ccf/yr in true heating climates.

  2. Enrique
    Posted May 18, 2007 at 10:17 am | Permalink

    For the average person, The Green Yahoo website is very practical. It gave me a guide on how and what to change to emitt less CO2.
    I came out with 15 tons of savings.
    I believe the next step is to created a website that would published the products and their efficiencies. For example, Which CFL light bulb has the less mercury and it last longer than other CFL lights bulbs. Which solar panel is most productive on producing energy and it is cost effective.
    Bill and Lisa great work on the website.

  3. Posted May 18, 2007 at 10:42 am | Permalink

    Hi Energy Guy,

    Thanks for looking through the site so thoroughly! I’m sure the Yahoo! group will be happy to get your feedback.

    We gave numbers to Yahoo! based on their list of action items. Yahoo! also decided to include some un-quantified items on the checklist.

    As you note, some of the items can be broken down into smaller changes. However, every calculator has to find a balance between usability and accuracy. In this case Yahoo! had to make the call.

    I think they did a pretty good job and that the calculator gives people a rough but useful idea of the difference simple changes can make. However, it’s a judgment call and reasonable people can disagree.

    All of our sources are listed. If you know of a more recent report for any of the items, please send it along.


  4. Energy Guy
    Posted May 18, 2007 at 11:12 am | Permalink

    I agree that it does a pretty good job, but still think that it needs some fixes along the lines of what I listed. The worst item is lumping in hybrids with a 10% mpg boost – you should either remove hybrid from the description or give it a separate line. Also, you should remove any item that gives no benefit or a negative benefit because it gives incorrect feedback to people thinking of doing that item if it really does save. I also think that it doesn’t help someone prioritize very well because of the averaging — insulating empty walls is often the biggest savings you can get, but it is watered down in the calculator.

    I do energy program evaluation and research on retrofit savings for a living (for the past 20+ years) but don’t have the time right now to produce a detailed bibliography for you. You could start with the AGA report I mentioned which has average gas usage of furnaces (Residential Natural Gas Market Survey December 2006) that would change many of your savings estimates.

    Also, the showerhead error should be easy for you to find a better estimate — there have been a few measured results from studies in the Northwest and California that have all found much lower gpm.

  5. Posted May 21, 2007 at 5:13 pm | Permalink

    Hi Energy Guy,

    We’ve sent your feedback to Yahoo!, and their design team is considering your suggestions. Thanks again for your interest and careful reading!


  6. Posted May 22, 2007 at 12:54 pm | Permalink

    Hi Enrique,

    I’m glad you liked the calculator!

    You’re absolutely right that it would be great to have an all-in-one comparison of these sorts of products. There isn’t one that I’m aware of, but for now here are some resources:

    The Energy Star site has a chart listing a huge number of compact fluorescent bulbs. The chart does not include mercury content but does show energy efficiency and lifetime. We have a guide to CFLs that has user reviews for some of these bulbs. We try to add to the guide whenever we can, so send in your reviews!

    Finally, many home appliances come with an EnergyGuide label that can help you compare energy efficiency of different makes and models.


  7. farmerchuck
    Posted July 9, 2007 at 1:34 pm | Permalink

    according to the yahoo carbon calculator, I have an above average carbon footprint, as the calculator doesn’t take into account measures that we have already taken…factor those in, and we have a negative footprint…

  8. Posted July 9, 2007 at 3:29 pm | Permalink

    Hi farmerchuck! Thanks for moseying over from DKos.

    You’re right, the calculator does not have everything. I’m glad that in your case those missing items mean you’re “under average”. How much of that is land management?

    PS – you might be interested in checking out Environmental Defense’s other blog, The Ruminant. Scott’s posts are enlightening and funny.

  9. Posted July 9, 2007 at 3:56 pm | Permalink

    Hi again farmerchuck,

    Bill asked me to post this on his behalf:

    “Be careful he doesn’t double count his carbon sequestration efforts. In a low-C market, land management practices that increase C in soils and vegetation can be sold in the market place as C offsets. (There is a voluntary market for these offsets today.) If he does that he can’t also take credit for these practices for his personal C footprint.”

    Sounds to me like a win-win, really. Either you’re accidentally double-counting while helping climate, or helping climate and soon to be profiting from the carbon market.

  10. anthrobus13
    Posted September 23, 2008 at 12:45 am | Permalink

    Hi Lisa,

    Im from Malaysia and have been researching on how to develop a carbon calculator for my country and I came across your post. My problem is, I dont know where to start – what kind of figures should I be looking for? How do I calculate carbon emissions? IF you can point me in the right direction, I would be very grateful.


  11. Posted September 23, 2008 at 5:07 pm | Permalink

    Hi anthrobus13,

    Great questions! To get an idea of the sorts of data you need, take a look at what we used for our calculator. For some things you will need Malaysia-specific statistics, such as emissions per kWh of electricity. Few countries have as much detailed data as the U.S., so you will probably need to make some crude assumptions for some factors. First, though, see what’s out there. The International Atomic Energy Agency is a good place to start. Good luck and have fun!

  12. Posted January 24, 2010 at 1:29 am | Permalink

    Interesting read! I have been looking to save money on my power costs since money is lower these days. I found your post very helpful. Thanks