Now consider a less sophisticated but equally troublesome form of trash — plastic bags. Polyethylene-based bags are hazardous to produce and, once discarded, can take up to 1,000 years to decompose. The bags are all but omnipresent: Consumers in the U.K. go through 8 billion per year; four out of five shoppers in the U.S. use plastic bags over paper or cloth; and the bags are so commonly seen tangled in trees and fence posts in South Africa that they’ve been called the national flower. Some countries, however, have drawn the line. In March, Bangladesh banned polyethylene bags after they were shown to have blocked drainage systems and contributed to severe flooding in 1988 and 1998. Taiwan hopes to prohibit free distribution of plastic bags, Singapore is launching an awareness campaign, and the Irish have slapped a hefty tax on their use. The latter was so effective that plastic bag distribution at one of the nation’s biggest chains has fallen by 97.5 percent.