Asked by: Elena Lytrides, Cardiff

The best source of data on CO2 emissions I've found is CARMA - Carbon Monitoring for Action ( It lists emissions from 50,000 power plants worldwide. It's a significant body of data given that power generation accounts for about a quarter of global carbon dioxide emissions at 10 billion tonnes per year.

Over a quarter of that comes from the 8000 power plants in the United States, making its energy sector the biggest carbon emitter in the world. China is second in the table, accounting for roughly another quarter of the global total. The UK is ninth, emitting 0.2 billion tonnes.

At absolute best, coal and nuclear power stations run at 50 per cent efficiency, so even a conservative estimate suggests that wastage from energy plants contributes to five billion tonnes of CO2 annually.

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