Coal is a disaster in environmental terms, from the destruction caused by mining it to the planet-warming carbon dioxide emitted when it is burned. Now it turns out even just transporting the stuff around is having a significant climate impact.
Carbon emissions from transporting coal by rail to power stations are around three times greater than previous estimates, according to 聽by John Sherwood of Clemson University, South Carolina and colleagues. In the worst cases, an extraordinary 35 per cent of overall CO2 emissions from coal use came from rail transport.
Sherwood鈥檚 team started with government data on what coal is burned where. They then plotted the location of each power station and used data from life-cycle analyses of diesel trains to work out how much CO2 is emitted transporting coal from mine to plant.
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Previous studies have suggested that transport emissions are only around 1 per cent of the total CO2 emissions from the use of coal for power, typically less than the emissions from mining. And for most plants in the US this is about right. But for around 1 in 10 power plants transport emissions are much higher, pushing the average up to 3.5 per cent, the team found.
鈥淭here are a few outliers that are kinda of scary when you think about it,鈥� says Sherwood, who presented the findings at a meeting of the American Geophysical Union in Washington DC on 12 December.
The findings are surprising as have found that transport emissions are small even when coal is exported to other countries. But Sherwood鈥檚聽work is far more detailed than previous analyses.
The team found that environmental legislation could be creating some perverse incentives. The study suggests some power plants are transporting low-sulphur coal thousands of kilometres, rather than burning high-sulphur coal available locally. That may be because if they burned high-sulphur coal, the plants would have to install sulphur scrubbers to comply with air pollution laws.
At the latest climate talks in Katrowice, Poland, the US and Australia . Sherwood鈥檚 findings are a reminder that making coal clean requires far more than capturing and storing the CO2 produced when coal is burned.
