New Zealand scientists are developing a better way of estimating carbon dioxide emissions from fossil fuel power stations.
The new analysis method tests the carbon content of grass growing nearby.
GNS researcher Jocelyn Turnbull said that if the grass contained a carbon isotope called radiocarbon, then it probably came from carbon dioxide found naturally in the atmosphere.
But if there was little radiocarbon it probably came from carbon dioxide emitted by the power plant.
"When plants grow by photosynthesising carbon dioxide - the carbon in that carbon dioxide gets laid down in the plant material.
"Fossil fuels which have been in the earth for many millions of years have no radiocarbon left in them, whereas all the natural carbon dioxide in the atmosphere has radiocarbon in it because it's being constantly generated by cosmic rays," Ms Turnbull said.