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This question is basically a follow-up question on something EnergyNumbers mentioned in his answer to this now closed question. He wrote that

together, our impact (on fighting global warming) can be huge .... The main thing is to work out where your biggest personal impact is, and to start there.

My question is: how do I determine what my biggest personal impact is on global warming and greenhouse gas emissions?

Ideally I would need to calculate the carbon footprint of all products I buy and activities I do, but that doesn't really seem feasible. Or are there any tools or standard calculations that can help here? I know there are carbon footprint calculators and ecological footprint calculators freely available on the internet but AFAIK these only show you one single measure as end result. I haven’t been able to find a calculator that identifies a top 5 of worst activities I do or products I buy from a sustainability point of view.

I realize this is a rather broad question and a lot of factors are probably involved. Perhaps an accurate answer will be too long to provide here. To narrow it down a bit more, my main interest is in tools, tips or starting points for researching my personal impact myself.

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I share your frustration with some of the online "carbon footprint" calculators, but if you really care about analyzing the components of your impact, you can still get useful information out of them.

First, I think a disclaimer is necessary. Any such calculation is going to have to make quite a few assumptions. Some assumptions may lead to slightly skewed results in individual cases, but averaged over all cases, they do a reasonable job. In general, it's still a better way to estimate your impact than it would be to simply rely on intuition, which sadly is what most people (even the eco-sensitive among us) do.

I also think it's important not to make the perfect the enemy of the good. We in the developed world probably need to reduce our carbon footprints by about 80% (or 90% in places like the US, Canada and Australia), so it's better to start cutting now, where you can, than to wait for the perfect data to guide you.

Online Calculators

With that said, here's a list of some online carbon footprint calculators (US-biased, I should note).

If you look at the US Environmental Protection Agency's calculator, they actually let you download the spreadsheet containing their math, directly. You can use that to hone in on your family's problem areas.

This nature.org calculator does actually produce a pie chart at the end of your input, showing relative contributions to your carbon footprint:

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Typical Scenarios

I think using a combination of online carbon footprint calculators is the best bet to get a pretty good feeling for where you contribute the most to global warming. But, for many people, these tend to be problem areas (with links for further reading):

  • Food - what type of diet do you have? Meat, then poultry and fish, and then fruits and veggies tend to have the biggest impacts on greenhouse gas emissions (not just carbon, but methane from agriculture is a big problem, especially in the "short" term of the next 100 years). Note: locality tends to be an overrated aspect of your food's impact, as transportation to market is a fairly small part of the energy required to produce food (it does matter, but not as much as choice of food types). Do you waste food (1/3 or more of food globally is wasted), or eat more than your body really needs (pleasure eating)?

  • Heating - how do you heat (or cool) your home? Homes like apartments or condos are fundamentally easier than houses to keep at a constant temperature, both because they tend to be smaller, and because each unit doesn't have 5 sides that are exposed to the outside air. Are you using a relatively efficient technology like a heat pump, or a less efficient one like electric baseboard heating? Is your home well-insulated? Do you keep your home warm in the winter, rather than turning down the thermostat and adding more clothing?

  • Local Transport - do you drive, or take the bus/walk? If you drive, do you drive electric (most efficient, and best for GHG if you use renewable electricity), use biodiesel (not as thermodynamically efficient, but most of the CO2 released was already in the air), drive a hybrid, a petro-diesel or gasoline car? For the most part, that's the order of least to most impact on global warming (with each general technology having a range depending on many factors).

  • Flying - airline travel is horrible for climate change. Not only does it consume massive quantities of fossil fuels in a short period of time, but it's going to be much more difficult to green commercial aviation than it is to green automobiles, because power-to-weight ratio is so critical in airplanes. There isn't a huge difference in impact between flying and driving to the same remote destination, but the choice really is whether to take those long trips at all. If you fly, especially across oceans (e.g. regularly for business or vacations), your raw carbon footprint will be large, no matter what else you do.

  • General Consumption - do you buy a lot of stuff? Toys for kids. New tools for your home or garden. New appliances with more features. Big TVs. New clothes when old ones are out of style. Everything we buy takes energy to make. When we throw it away (or even recycle it), it causes more energy to be used, and greenhouse gases to be produced (e.g. trash decomposing in landfills). Getting into the mindset of buying only what you need, not just what you want, and keeping things you buy for a long time (or fixing them when they break), can reduce your impact substantially.

  • Reproduction - this isn't going to make people happy, as it's a taboo subject, but the number of children you have has a huge impact on climate change. It's important not to get lured into the trap of considering only per capita carbon footprints, because the environment knows nothing about the number of people ... only the total amount of greenhouse gas we produce. More people mean more emissions, and at 7 billion and counting, it's simply no longer a reasonable argument to contend that we need to produce 2+ children per couple to sustain the human race. Parents also frequently fall into the trap of thinking that because they live an eco-friendly lifestyle, their children will, too, when grown. Kids are influenced by their parents, but also by the society they live in. Right now, their society is a profoundly negative influence in this regard.

  • Pets - while this is another issue that upsets people, choosing to keep pets is a significant part of many families' impacts. It certainly depends on the animal, its size, and activity level. But, a large dog can easily add as much greenhouse gas in a year (mostly due to the fact that it probably consumes a meat-intensive, high-calorie diet) as an SUV.

  • Home Electricity (non-HVAC) - I'm going to gloss over this one, both because it's comprised of many small contributors and because I think many who read this will already have taken obvious steps, like using energy-efficient lighting. I think the other issues are more likely to make it into your top 5 list.

  • Great answer! I especially like the EPA spreadsheet. – THelper Jun 7 '13 at 10:45
  • @THelper, yes, we engineers are usually lovers of spreadsheets :) – Nate Jun 7 '13 at 20:56
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Nothing will beat doing an audit, particularly once you have made progress on the really obvious stuff shown by generic calculators.

My wife compiled a spreadsheet of emissions embodied in many activities and products, with a ledger you can fill out as you go. Measure everything you consume or dispose of for a period, then cut back to tracking unusual items and whatever you found was a big contributor.

Some data is location dependent (e.g. standard beef in NZ is grass fed but yours may not be) and all data contains a degree of approximation, so she provided extensive notes on sources. Some of your measurements may also be estimates - we decided to just go with the council estimate for sewage volume. :-)

The spreadsheet is provided under a Creative Commons license. We would love feedback on how it works for other people. For a contact form and more discussion of background see this overly purple page.

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    Fun fact: dark-colored web pages with white font are actually better for reducing energy consumption in computer monitors :) – Nate Jun 6 '13 at 8:31
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    @Nate: that used to be true for all monitors, when we used CRTs. With LCDs, only those which support "dynamic dimming" (a minority) will actually benefit from the dark image. The others just blast the light like for a white image and then block it with the crystal matrix. They actually consume more energy displaying a dark image. – André Paramés Jun 12 '13 at 10:41
  • @AndréParamés, the article you link to is from 2007. First of all, a quote from that article states "All of the scientific test data we have come across shows a slight saving on black LCD screens". That doesn't really support the article's, or your, conclusion. The article also states that it's not just dynamic dimming, but also LED backlit LCDs or AMOLEDs, that use less power with black screens. Also, from this 2010 article, LED backlit screens should already have taken over most of the market. – Nate Jun 25 '13 at 21:09
  • @Nate: This has been asked twice on Sceptic Stack Exchange: skeptics.stackexchange.com/questions/4373/… and (as a duplicate) skeptics.stackexchange.com/questions/24087/… . – PJTraill Nov 15 '17 at 12:08

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