Many of the green plastic looking bags for vegetables in grocery stores are enviornmentally good.
In a few thousand years for a plastic bags but keep in mind that if it biodegrades, the carbon become carbon dioxide, the plastic bags are made from natural gas which are a byproduct of oil production and most natural gas are actually burned in flares at the well site so if the plastic bag isn't made, the gas would be burned. Whether the plastic bag is thrown into a landfill or recycled, the carbon is sequestered, we are spending millions trying to sequester carbon to protect the environment so how does not having the bag biodegrade be bad for the environment?
Some plastic bags are biodegradable some are not. evidence currently suggests that most plastic bags are degrading quicker than was originally though they would. This could be because bacteria are evolving ways to feed on them, This has happened with nylon. Some bags breakdown quite quickly provided they are exposed to sunlight, but this is not much good if they are buried in a land fill.
Paper bags are of course degradable as are things like cotton, but in land fill without any oxygen it can still take many years.
What kind of bag are you talking about?
A pure paper bag is biodegradable, but something like a synthetic paper, waxed paper, or plastic bag isn't as biodegradable.
Compare to plastic bags and paper bags cloth bags can last longer and it is re-usable meaning that plastic bags and paper bags is an one time use only and after that it will be thrown to the garbage and will end up in land fills. Using plastic bags help reduce the waste
Conventional plastics can be made to biodegrade rather quickly in landfills, if they are made with Earth Nurture Additive. See: http://earthnurture.com .
Not now, maybe in future.
Sometimes...
