Over two years ago a comprehensive and independently peer-reviewed Life Cycle Analysis was completed on the environmental impact of natural corks, aluminium screw caps, and plastic closures.  It was audited by PricewaterhouseCoopers.

The study found that CO₂ emissions — a key factor in global warming — resulting from the life cycle of a screwcap are 24 times higher than those from a natural cork stopper, while a plastic stopper is responsible for 10 times more CO₂ than a natural cork.

The study included analyses of seven key environmental indicators: the emission of greenhouse gases; consumption of non-renewable energy; consumption of water; contribution to the acidification of the atmosphere; contribution to the deterioration of the ozone layer; contribution to eutrophication (nutrient build-up); and production of solid waste.

Cork stoppers emerged as the best alternative against six indicators and were placed second, behind aluminium closures, in relation to water consumption.

Despite the clear evidence that screw caps are the most environmentally unfriendly wine bottle closure on the planet, to our knowledge in the past two years there has been no appreciable shift away from screw caps by the wineries that use them, including those touting their small carbon footprint.  Further, there is little evidence fans of screw caps have toned down their rhetoric.