(CNN) -- As a concept, recycling has lived and died many times throughout its 4,000-year old history. But it always re-emerges as an idea when humans need it most, such as during the Great Depression, and later during World War II, when American companies recycled or reused around 25 percent of the waste stream.





A sign in Cheshire, England signalling a recycling drop-off area.





Today, the global recycling industry generates $160 billion a year, processing more than 500 million tons of materials.





The industry is becoming one of the world's biggest employers. While the official amount of people employed by the industry is 1.5 million worldwide, the real figure -- when you factor in illegal recycling operations in the developing world -- is likely to be much, much higher. The United Nations believes, for example, that as many as 10 million people in China alone are now in the recycling business.





What's not to like about recycling?





There are some fairly persuasive arguments for recycling, and for using recycled goods. Energy savings is just one of them. By reusing existing materials you are essentially removing the process involved in sourcing the "virgin materials" in the first place.





Take soda cans, made from aluminum. According to Friends of the Earth, creating a ton of these from scratch takes five times the amount of energy as it would to produce a ton of recycled cans. According to the Bureau of International Recycling (BIR), the companies that manufacture recycled aluminum are using 95 percent less energy than if they were using "virgin materials." (For plastics the energy savings are almost as high -- 80 percent, BIR says, while making paper from recycled paper (as opposed to wood) can save 64 percent of energy.)





Looking at it another way, according to the National Recycling Coalition, the amount of energy saved in one year by Americans recycling their soda cans, plastic containers, newspapers and packaging represented the energy equivalent of:





Not surprisingly, recycling also impacts pollution levels. BIR says producing paper from recycled paper as opposed to wood can slash air pollution by as much as 74 percent and water pollution by 35 percent; while manufacturing recycled steel results in 86 percent less air pollution.





There are different types of pollution savings to be made, reducing the pollution generated by manufacturing the stuff in the first place. And then there is the pollution that results in dumping the waste in landfills, instead of recycling it. A recent report from the European Environment Agency (EEA), for example, has predicted that greenhouse gas emissions from household waste will drop by more than 80 percent by 2020 -- largely because of increases in recycling levels which are diverting waste away from landfills.





And the carbon savings can be huge, even when a relatively small amount of effort has been made. The UK has one of Europe's lowest recycling rates when it comes to municipal waste -- 27 percent. Yet, the impact on its carbon emissions has already become worthwhile, according to Waste & Resources Action Programme, or WRAP. WRAP says that these relatively minor efforts already mean a 10 million- to 15 million-ton reduction in carbon dioxide (CO2) emissions a year -- the equivalent of taking 3.5 million cars off the road.





What about the costs? One of the main objections to the recycling movement has been the cost factor. Throwing something away is obviously going to be a lot cheaper than going through the hassle of recycling it. And certain materials are going to be a lot tougher to recycle than others, driving up costs and energy spent. But, as a 2004 study by research group GPI Atlantic found out, there are many different ways to measure cost.





GPI looked at the Canadian province of Nova Scotia, which back in the 1990s had decided that 50 percent of its trash was going to get recycled instead of landing up in incinerators or landfills. The annual cost to the province of doing this was $18 million more than it would have cost to chuck trash away. But, when different factors were considered, the number looked very different These factors included
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