Environmentalists will often answer the question "Which is better, paper carry bags or plastic bags" with "neither".
But I believe that most research indicates that plastic bags have lesser impact on environment than its paper counter parts.
Here is one reason why:
Issue 1: Energy and natural resources used to manufacture plastic bags Vs paper bags. It takes more than four times as much energy to manufacture a paper bag as it does to manufacture a plastic bag.
ENERGY TO PRODUCE BAG ORIGINALLY
(BTUs British Thermal Units)
Safeway Plastic Bags: 594 BTUs
Safeway Paper Bags: 2511 BTUs
(Source: 1989 Plastic Recycling Directory, Society of Plastics Industry.)
What does this mean? It means that Plastic bags take less energy to create, which is significant because so much of our energy comes from dirty sources like coal and petroleum.
Of course, most paper comes from tree pulp, so the impact of paper bag production on forests is enormous.
In 1999, 14 million trees were cut to produce the 10 billion paper grocery bags used by Americans that year alone.
Paper bag production delivers a global warming double-whammy.
Forests, which are major absorbers of greenhouse gases - have to be cut down. And then there is the subsequent manufacturing process of bags produces greenhouse gases.
Issue 2: Pollution
The majority of kraft paper is made by heating wood chips under pressure at high temperatures in a chemical solution. As evidenced by the unmistakable stench commonly associated with paper mills, the use of these toxic chemicals contributes to both air pollution, such as acid rain, and water pollution. Millions of gallons of these chemicals pour into our waterways each year; the toxicity of the chemicals is long-term and settles into the sediments, working its way through the food chain.
POLLUTANTS PAPER V.S. PLASTIC
Paper sacks generate 70% more air and 50 times more water pollutants than plastic bags.
Source: "Comparison of the Effects on the Environment of Polyethylene and Paper Carrier Bags," Federal Office of the Environment, August 1988
According to a life cycle analysis by Franklin Associates Ltd, plastic bags create fewer airborne emissions and require less energy during the life cycle of both types of bags per 10,000 equivalent uses -- plastic creates 9.1 cubic pounds of solid waste vs. 45.8 cubic pounds for paper; plastic creates 17.9 pounds of atmospheric emissions vs. 64.2 pounds for paper; plastic creates 1.8 pounds of waterborne waste vs. 31.2 pounds for paper.
Issue 3: Recycling
It takes 91% less energy to recycle a pound of plastic than it takes to recycle a pound of paper. But recycling rates of either type of disposable bag are extremely low, with only 10 to 15% of paper bags and 1 to 3% of plastic bags being recycled, according to the Wall Street Journal.
ENERGY TO RECYCLE PACKAGE ONCE (BTUs)
Safeway Plastic Bags: 17 BTUs
Safeway Paper Bags: 1444 BTUs
Source: 1989 Plastic Recycling Directory, Society of Plastics Industry.
Although paper bags have a higher recycling rate than plastic, each new paper grocery bag you use is made from mostly virgin pulp for better strength and elasticity.
Issue 4: Transportation
Paper is an extremely dense material that is much heavier than plastic, and hence requires higher transport costs to move around.
Maxpak supply similar sizes of string handle paper bags, and plain plastic singlet bags.
An 11 kg carton holds 2000 plastic bags. A similar weight carton holds only 250 paper bags(this carton is double the volume) Our truck has a 10 tonne carrying capacity. This means it can carry around 900 cartons which is 1.8 million plastic bags or 225,000 paper bag. For every 1 truck load of plastic bags, you would need 8 truck loads to carry the same amount of paper bags! That is 8 times the amount of energy, fuel and carbon emmisions just for local transportation.
The most negative environmental impact that plastic bags represent is their persistence in the environment as litter. Emotive images of animals in distress and litter in our streets, parks and waterways deeply affect the public consciousness. This is a human behaviour issue I believe. They look terrible as litter - but bag's don't litter themselves - humans do. Paper bags are just as likely to become litter as plastic.
I really encourage you to do some research of your own - to verify my commentary, as well as to find a variety of views. You'll find a robust debate all over the internet. A google query "are paper bags better than plastic?" will reveal a plethora of information. I'll put a few links below for you to check out if you have time.