Fossil fuels currently power the shipping industrySven Hansche/ShutterstockSwitching from burning fossil fuels to burning ammonia is a promising way for the shipping industry to cut its carbon dioxide emissions. But if it isnt careful, this swap could also boost harmful nitrogen pollution.Thats a major alarm bell thats ringing, says Xin Zhang at the University of Maryland.The tens of thousands of ships on the oceans are responsible for about 3 per cent of global CO2 emissions, burning more than 300