Comment by netjiro | Hacker News Reader

Comment by netjiro | Hacker News Reader

> biking (8 g) or walking (0 g) [per mile]

This is simply wrong. It doesn't take into account the CO2 footprint of the person doing the biking or walking. Biking is more efficient than walking per km. Since anyone biking, running, walking would be eating more to cover the exercise this can have a significant footprint based on what their diet looks like. A running beef eater vs a running vegan looks very different.

I used to bike 65km/d round trip to work. Wonderful for my mind and body, but I had to eat at least one extra meal every day for the periods I was active, around 200-300g total.

Normally I would replenish with fried eggs and potatoes at a guesstimated 4x (CO2 equivalent mass ratio), which is (meh) reasonable? Giving around 13g/km footprint for biking (just from my food).

Assuming I would be eating lamb or beef at somewhere around 30x impact, that extra meal would give a biking footprint around 92g/km just from my food!

Correct my numbers or methods if you disagree.

[edit]: Comparison to my (tiny) car at the time burning 4.5l/100km, (2.3kg CO2 / litre petrol), the car would be around 103g/km, which is not much higher than me on a bicycle if I kept a shitty diet !!

If you are taking into account the food consumption of the participants, why stop at one mode? What about the food consumed by the people involved in the production and fuel for cars and scooters? How much would you include? Is it the same for someone sitting at a desk vs someone working on a production line somewhere? Does the existence of a regular job on a car production line encourage larger families? It gets nuts fast which is why it doesn't really make a lot of sense to try to take into account food intake for various transportation modes.

If you do manage to convince someone to take their car rather than their bike then how can you be sure they are not going sneak off and get their daily exercise some other way? Normally exercise from walking/biking reduces the need for other exercise. In a sense the extra food cost is free.

Re: the car, don't forget the impact of producing the car, and the totalt impact of the fossil fuel production chain.

Absolutely. But I already had the car, and it was later replaced due to old age and not due to distance driven. But the baseline metabolic burn of the 20min car ride should be taken into account, and was, since I was only comparing the extra meal I had to eat vs the extra gas I would have burned.

The total impact of the fossile fuel production chain is something I've been looking for, but not found any good numbers on yet.

I assume that petrol from saudi shallow wells is drastically different from canadian tar sand?

Anyone with reliable data on this?

Found some info from late 2018, but paywalled and incomplete, focusing on oil wells.

https://news.stanford.edu/2018/08/30/measuring-crude-oils-ca...

https://science.sciencemag.org/content/361/6405/851.summary

Older data from 2013 regarding tar sand production is much worse

https://insideclimatenews.org/news/20130219/oil-sands-mining...

Then, in the end, general refineries have ca 85% energy efficiency for petrol and diesel, discounting other factors.

> It doesn't take into account the CO2 footprint of the person doing the biking or walking.

This is carbon neutral because all the CO2 we exhale comes from atmospheric CO2 captured by plants (and then through the food chain up to us).

Now, of course food production has a carbon footprint because of harvesting, transport, processing, etc. but it quickly gets hugely complex to measure.

In any case, for the purpose of comparison they obviously restricted to the impact of the mean of transport. Your food or your carbon footprint in general does not change anything about that.

I think you underestimate the fossile fuel expenditure from agriculture, transportation, wastage, etc.

But it is true that if I walk into a forest and eat a wild grown apple, that CO2 is then from and in the normal carbon cycle and not any added fossile carbon.

[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2935130/

[2] https://foodprint.org/issues/agriculture-energy-consumption/

Perhaps it would be better if I clarified my statement as GHG-(CO2 equivalent)?

Wasn't the CO2 in fossile fuel also ultimately captured from the atmosphere by plants?

?

Yes, but fossile carbon is out of the carbon cycle, stored underground until we dig it up? This is a fairly fundamental pillar in the discussion around environmental impact of GHG emissions?

Yes, fossil fuels are originally from organic life, which resulted directly or indirectly from photosynthesis.

Plants do their best to suck up all the CO2 in the atmosphere. Yet CO2 is being added to the atmosphere faster than photosynthesis can capture it. This is why CO2 levels are rising. Human activity contributes a lot to the addition of CO2 (and equivalent greenhouse gases) and plants can't keep up with us.

Yes, captured and stored at a time when there was many times as much CO2 in the atmosphere. Release it, and you return the atmosphere to its former condition.

> I think you underestimate the fossile fuel expenditure from agriculture, transportation, wastage, etc.

No, I'm saying that this is irrelevant when comparing means of personal transportation...

The fact remain that the biological food chain is carbon neutral. As I already said, and as you also mentionend, it is the industrial production chain that is not.

That is an absurd argument. The modern food chain is not carbon neutral [0].

If I start running to work, I have to consume more food. If I have a vegan diet I am eating the direct result of photosynthesis. That is, we could imagine the embodied carbon of my apple resulted directly from my previous exhalation of CO2. I do not dispute that some part of the 'life cycle of food' is a closed loop in this regard.

Yet I can't just 'eat an apple'. I also require someone to grow the apple (with fertilizer and its GHG emitting production chain), protect it (likely with pesticides), clean and package, transport, store and sell the apple. By the time I chew into the apple I have already contributed to the demand of GHG emitting processes.

So if you want to rigorously compare scooters with walking, running or riding a horse (all which affect quantity of food consumed), you need to take into account the carbon footprint of food. Just as when you look at GHG emissions of fuel, you don't just look at its combustion - you look at the supply chain.

If you only look at where carbon is added (e.g. fossil fuel combustion) or removed (e.g. carbon forest sinks) from the cycle, you miss out on learning about how individual actions or choices affect the rate at which addition or subtraction occurs.

[0] - https://www.researchgate.net/profile/Henk_Westhoek/publicati...

> I have to consume more food.

Most people probably don't, and many people could afford to both run to work and eat less.

My environmental studies prof did an experiment cycling and getting the bus to university on both the amounnt of money spent and energy consumed. He found that he would spend more if cycling than the bus fare on food to keep the same energy input equal.

People also generally cannot sustain eating less continually but obviously there's a health benefit from some changes.

The ecosystem approach to food energy and carbon brings some surprising convulsions too. For example wrapping and selling fruit in plastic bags is better than buying them loose. This doesn't make sense unless you think about the whole picture.

I suspect that the recent HN craze for indiscriminate feel good tree planting is also ecologically and sustainably suspect if looked at holistically.

You're right that a lot of people eat more than they should, and exercise less than they should. We aren't efficient in this regard.

Yet when a human exercises, they breathe more, and produce more CO2. There is an internal carbon cycle that must be maintained. If any person exercises more without changing their diet, their rate of 'carbon accumulation' (to be kind) will decrease. For someone like myself who isn't in the habit of accumulating carbon - a long-term impact of riding to work will be that I will lose weight [0]. As a carbon-based life form, if I don't change this to be non-negative, I'm clearly down a path of self-destruction, and will need to increase my food intake eventually.

[0] - https://pdfs.semanticscholar.org/f407/588843385c964c7de0bc9e...

The biological food chain is perfectly carbon neutral, whether you eat meat or not.

But, as I wrote in my previous comment, the industrial production chain may not be, and in fact isn't.

In any case, this is a red herring because that makes no difference when comparing means of personal transportation: Whether I walk or ride an electric scooter I will have to eat very close to the same, close enough to be a rounding error.

For the extra energy you can and probably would eat the lowest carbon food available which is going to be stuff like rice and pasta. You are not going to have the digestive capacity to metabolize a lot of extra meat just for energy which you would tend to avoid for economic reasons.

Just existing takes the majority of energy for warm blooded creatures so the percentage increase due to an increase of physical activity is relatively small.

Physical activity is the cure for many medical conditions. Medical treatment has a carbon cost, probably a significant one.

> like rice

Rice has pretty high carbon footprint.

https://www.independent.co.uk/environment/rice-farming-clima...

The article actually talks about methane and nitrous oxide emissions and gives no numbers to allow any sort of comparison.

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