In addition to the environmental benefits already mentioned, there is the
fact that breastfeeding delays the return of menstrual periods and therefore
reduces the need for sanitary pads and tampons (and their disposal).  It
increases child spacing, and therefore helps fight the population explosiion
with its attendant strain on the world's resources.
Every woman who breastfeeds means less bovine milk is required to be turned
into infant formula.  Every cow bred for milk production needs pasture and
this usually means land clearing.  So breastfeeding saves forests.  It would
take 114 million lactating cows grazing on cleared pasture to replace the
milk of all the breastfeeding mothers of India alone.
All those cows produce methane and increased methane levels speed up the
greenhouse effect.  Incidentally, I read the other day that breastfed babies
don't produce any methane at all!  I presume this in only while they're
fully breastfed.
It's great stuff, breastmilk.

Lesley McBurney, Brisbane, Australia.