Most are heavy 900 gram (about 2 pounds) descendants from the original bottle design by the Benedictine monk Dom Pérignon in the 1600s. They may have worked pretty well for 350 years or so, but they use a bunch of sand, are expensive and energy intensive to make, heavy to transport, and an awful lot of glass to try and recycle.
Turns out the Champagne industry has recognized this and is working on a lighter bottle that could save up to 8,000 metric tons of carbon a year. The design process is described in a NY Times piece today by Liz Alderman.
The image above is by Stéphane Lavoué for the International Herald Tribune.