It may not be, too! Calculating the lifecycle is complex. But it isn't something than is easy to assume one way or the other.
>and are fully recyclable
How about after mixing them with a bunch of limestone? Generally "hybrid" materials aren't recyclable (tetrapacks, mylar bags, wet strength cardboard, etc).
So I know limestone is technically a non-renewable resource, since we're using it far faster than it is being created.
Should, uh, we actually be worried? It's like 7% of the Earth's crust; are we actually using limestone fast enough to use up a significant fraction of the usable limestone in the expected lifetime of humanity?
http://www.bbc.com/future/story/20120618-global-resources-st...
It lists a variety of elements (like antimony) that are surprisingly constrained. If I were to pick the most critical material on the list, though, it would be phosphates. The green boom that feeds the world needs phosphates, the world supply of phosphate-bearing rock is small, and there are no possible substitutes.
This is not the safe bet many people think. If you look at the entire lifecycle of a product, plastic bags (to take an example) have a better footprint across the board than paper ones.
http://www.alternet.org/environment/whats-better-environment...
I have some that have lasted for years now.
I would guess that heavy-duty plastic would fare significantly better, because cotton in general is an awful crop from an energy input standpoint, but I can't give you a more precise answer than that, I'm afraid.
Importantly we don't factor in destruction of the planet: use of non-renewable oil and pollution (and is impact on food supplies, etc.). This is where the cost seems higher with disposable plastic, a cost we are yet to pay.
I don't want to minimize the difficulty of this- it's really, really hard to get right. But we do learn things, and (perhaps most importantly) we learn counter-intuitive things. And one of them is that plastics, even taking the tremendous problems with garbage patches in the ocean and the like, and not the clear-cut negative that our emotional side tends to think.
That said I do not use paper bags or plastic bags but a recycled canvas bag I've used for hundreds of shopping trips.
//
The more energy it takes to make something, the greater the potential environmental impact.
Plastic in the ocean is awful. The vast majority of it comes from just a few countries. What some westerner uses to take home their groceries isn't even a rounding error in terms of source waste.
https://www.fastcompany.com/3051847/most-of-the-plastic-in-t...
"even a rounding error in terms of source waste."
Reading the report says "Low-residual-value plastic waste is more likely to leak than high-value plastic [...] his means that products or packaging with low residual value (plastic shopping bags, for instance) are less likely to be collected; they therefore become a particularly significant contributor to ocean plastic"
Please also note that the biggest contributor, and the biggest reason for China being that contributor, is simple lack of a functional garbage collection system at all in large parts of the country.
I emphasize this because I think people tend to focus on the minutiae (ie, paper, plastic or canvas when it comes to grocery bags) when the bulk of the problem has nothing to do with bag choice, it has to due to a complete lack of wastestream infrastructure. It is understandable to a degree. The problem is so overwhelming, it feels like what one person can do is never going to be enough.