Carbon sins told by grass

We may not know it, but our carbon sins are being logged.

The tiny characters taking notes are silent but faithful scribes on climate change, and they outnumber all of us.

Scientists have found a way to use grass near power plants as a way of revealing the level of carbon dioxide they churn out.

‘‘When grass grows, it collects carbon dioxide (CO2) from the air, as all plants do,’’ Jocelyn Turnbull of GNS Science said.

This is photosynthesis – or how plants combine sunlight, water, and CO2 to produce oxygen and sugar. ‘‘That records the carbon dioxide in the air.’’

Due to the extreme age of coal and gas, carbon dioxide from combustion contains no radiocarbon, yet natural CO2 sources, such as humble blades of grass, are full of it, Turnbull said.

By measuring the amount of radiocarbon present, scientists can tell how much of the CO came from the power plant.

This process marks the method of independently verifying greenhouse gas emission rates that have previously only been self-reported by power firms using fossil fuels. It was developed by GNS Science.

The method can be used worldwide, so could help to keep other countries accountable on the promise they made under the Paris Climate Agreement (COP21) in December last year.

‘‘If we are paying another country to reduce it’s emissions, we want to know if they are actually doing that,’’ Turnbull said.

New Zealand was one of 195 countries that pledged to reduce carbon emissions, with aspirations to limit warming to 1.5 degrees Celsius above preindustrial levels.

New Zealand is already at 80 per cent renewable energy when it comes to fossil fuels, but the issue is a major one globally.

Since the closure of Huntly East Coal Mine in Waikato, New Zealand has no coal power plants, but some dairy factories were ‘‘extensive users’’ of coal for energy.

‘‘We’re already 1C warmer than pre-industrial levels, so there’s not a lot of room for movement.

‘‘Article 13 of the COP21 agreement states countries must show transparency in their efforts to reduce climate change. They have to do what they say they’ll do.’’

Turnbull said there was general interest from some international players, but the next step was to roll out the monitoring around Huntly to see how the plant fared when it was operational.