Hmm..I think they decompose fairly quickly — especially in sunlight.
Yup...It isn't 'centuries.'
It varies. Here we have just submitted to a no plastic bag regime.
OK I forget right. So I look behind the car seats. Find two bags some months old - no structural integrity left.
And one bag intact and sound, labeled "Biodegradable, will break down in landfill and sunlight". Thing is: producing and labelling that type of bag was a big enviro-friendly marketing campaign about 5+ years ago. Makes you think.