[positron26]

Can't imagine this survives napkin scrutiny. A ten mile drive isn't using nearly as much hydrocarbon mass as 10k plastic bags. While most of the plastic hopefully winds up in a landfill, most of the gasoline is water and carbon dioxide by the end. It's tires versus bags. While tires shed, the mass lost in 10min is definitely quite a bit lower than 10k bags or the fraction that escapes the waste pipeline.

[privatelypublic]

30mpg, 10 miles, means two pounds of gasoline, 910grams, knock off or add 100g for ethanol per your preference, a google says about 5grams per bag, so nearly 200 bags.

Nowhere close to 10k, but nontrivial. And, this gets reduced and sometimes outright negated if you reuse the bag. Doesn't mean we shouldn't evaluate if plastic shopping bags are the beat choice though.

I don't think replacing them with store bought doggy poo and cat litter bags is better. It's not a reduction and theres no reuse. If you find yourself discarding them outright, then find an alternative I guess.

[CalRobert]

Don’t forget that a lot of carbon went in to making the road, the parking (deforestation or other land destruction for those should be considered too), the car itself, emissions from tyre wear, brake dust, some plastic for the single use medical devices necessitated by treatment of people struck by drivers, etc etc.

Though what is often forgotten is the insane amounts of plastic used in farming. Occlusion fabric for weeds, polytunnel skins, silage wrap, etc

[privatelypublic]

I didn't forget, its just awfully hard to fit all that on a napkin.

[positron26]

I can breathe CO2. I don't want plastic in my brain. These two things are not the same.

[dz0707]

I think your math is wrong. Most of modern cars do up to 150g of CO2 per 100km, there are other emissions too, but they are in way smaller numbers.

[hedgehog]

I think the units there are off, a Camry hybrid is about 100g direct CO2 per km. One widely repeated calculation has total direct + indirect emissions for a grocery bag at 200g. So 1km driven vs 1 bag is a similar magnitude of emissions.

[privatelypublic]

Please be careful of such "metrics/statistics." Their very nature means they're politically and financially incentivized lean towards a higher or lower number than "the other guy." And, of course, a big number is scarier in a vacuum. What if a paper bag is 250g of emissions?

The poster child for me for this is low-GWP refrigerants. Sounds good, right? Well, think about how CO2 captured filtered and compressed compares. I'll leave everybody to argue with their-self on this. Does co2 vs r-whatever use more energy? Less? Does it somehow justify the emissions and pollution of manufacture?

My conclusion is... I don't know.

[hedgehog]

We have enough data to estimate the reasonable range of possibilities and exclude the upthread assertion that a ten minute car ride is similar emissions to 10k plastic bags. A degree of uncertainty need not make us helpless in the face of loud ignorance, that's how we end up giving equal weight in the media to common consensus of professionals in whatever field and political operatives with fringe beliefs but no evidence.

[privatelypublic]

Sorry, I screwed up and misread what you wrote- primarily, a simple "we can do way better than 30mpg." And theres not a lot in the way of wiggle room to debate with any integrity the amount of CO2 burning a set quantity of gas produces. A couple percentage points for NOx and friends and thats it.

I am confused why everybody mentions emissions though. In a discussion on paper/plastic/reusable bags, in a response to a call for napkin math for a claim of "10,000 bags from the fuel needed to get to the store" (essentially the argument made)- CO2 isn't relevant: just the mass of the gas used to get to the store.

I'm not pleased with how this turned out. to be told I'm wrong? That's fine, its the internet. I'm disappointed and alarmed with how badly wrong the suggested corrections are... it's deeply frustrating for me as well.

[privatelypublic]

Thats comically wrong. Human Resting metabolism is on the order of 20grams of CO2/hr.

See: https://www.sciencedirect.com/science/article/pii/S036013232...

As for a kilo of gas per 10 miles- see https://en.m.wikipedia.org/wiki/Gasoline - says 0.71-0.77g/mL, standard conversion table says 3.785L per gallon. (https://www.engineeringtoolbox.com/volume-units-converter-d_...), and finally- since we're comparing burning gas for a car vs using it in plastic: the figure of merit is petroleum usage, not greenhouse gas emission. Technically, plastic and gasoline aren't going to be 1:1. But that's not napkin math anymore unless you're a petroleum engineer/chemist.

[adastra22]

Also most of that weight is oxygen. The mass of carbon from the gasoline in an apples to apples comparison to plastic would be much lower.

It doesn't really make sense to be comparing plastic waste to CO2 emissions though. These aren't fungible.

[ahoka]

Cars don't only need gasoline to exist and work.

[gamblor956]

10 miles in a 30pmg vehicle uses only 1/3 of a pound of gasoline, or roughly 150g. So, nowhere close to 10k or even 1k...

150g is only equal to about 1-5 of the reusable bags in CA grocery stores, depending on the store.