It is a seductive vision. But it will involve a momentous effort and a lot of time and money to get there. There is no single switch we can flick to turn the entire Material World on to renewable energy. And it will necessitate extraordinary amounts of raw materials. Consider what it takes to replace a small natural gas turbine, pumping out 100 megawatts of electricity, enough for up to 100,000 homes, with wind power. You would need around 20 enormous wind turbines. To build those turbines you will need nearly 30,000 tonnes of iron and almost 50,000 tonnes of concrete, along with 900 tonnes of
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