That's what this article argues:
According to Tide, one can save up to 80% of energy per load by washing in cold. This is based on conversion from warm/cold to cold/cold cycle and using a vertical axis machine with electric water heater set at 140º F.
You might be interested in a Time Magazine piece which reports, "A recent study by Cambridge University's Institute of Manufacturing found that 60% of the energy associated with a piece of clothing is spent in washing and drying it. Over its lifetime, a T-shirt can send up to 9 lbs. of carbon dioxide into the air."