A University College Cork research team is assessing whether Irish grasslands may represent an enormous carbon sink that could help Ireland meet its carbon dioxide commitments under the Kyoto Protocol, writes Dick Ahlstrom.
The Republic is in deep trouble over international agreements on national reductions in carbon dioxide. The 1997 Kyoto Protocol and the 2001 Marrakech Accords set challenging limits for the release of this climate-changing greenhouse gas - and meeting them will be difficult.
The agreements allow, however, for a degree of horse-trading, weighing CO2 output against "carbon sinks", usually forestry plantations that help take the gas out of circulation as timber and leaf growth.
Researchers from University College Cork and Teagasc's Johnstown Castle centre in Wexford have joined forces to assess one of this island's greatest carbon sinks, not trees but grassland.
Initial results suggest that grassland could sequester almost half of all the CO2 produced in the State. Prof Gerard Kiely of the Civil and Environmental Engineering Department at UCC and Dr Owen Carton of Teagasc are studying carbon sequestration by measuring CO2 levels just above growing grass. The object is to measure the flux of the gas, not just its concentration, explains Kiely.
The flux gives the rise and fall of CO2 levels over time, indicating whether it is being taken out of the atmosphere during photosynthesis or being released by respiring grasses. "With these measurements we can quantify the daily, seasonal and yearly variation of the flux of CO2 and so determine how good or how bad grasslands are at sequestrating CO2," he says.
The five-year project is funded by the Government's RTDI programme and is managed by the Environmental Protection Agency. First measurements were taken last summer at a grassland site in the South and a second site will soon come on stream at Johnstown, says Kiely.
The team builds short metal towers to hold measuring equipment. The CO2 measuring device is known as an "open path infrared gas analyser", a high-frequency unit that records gas level and water vapour 10 times each second.
Wind speed and direction, temperature and "PAR" - photosynthetic action radiation or the amount of radiation able to drive photosynthesis - are also measured and plotted with the CO2 data. Gas measurements at the site are taken at 10 metres above ground. "The instrument sees a footprint 100 times its height," says Kiely. The Wexford site will measure at three metres.
The rapid sampling rate means wind direction and speed do not confound the results. The system is more than sensitive enough for the researchers to link CO2 levels and PAR, with the rise and fall of gas seen to vary due to sunlight.
"Early results from the first grassland site are particularly exciting," Kiely says. Measurements were taken during July through September 2001, showing that a hectare of grass could pull eight tonnes of CO2 out of the atmosphere. "While we do not yet have the results for a full year, we speculate that the intensively grazed grassland site that we are now examining may very well sequester about 10 tonnes of CO2 per hectare per year," he adds.
The Republic has about 3.1 million hectares of grassland, about 45 per cent of the total surface, and if the annual sequestration rate of 10 tonnes per hectare is correct then our green fields could extract 31 million tonnes of CO2 per year.
Work by others shows that in 1998 the Republic produced about 64 million tonnes of CO2 including about 20 million tonnes from agriculture.
"The tantalising question is, if Ireland takes 10 per cent of its intensively grazed grassland out of commission, say by 2010, will this have the effect of reducing CO2 sequestration nationally by about two million tonnes," Kiely says. He cautioned against early celebrations that the Republic has found a way out of its difficulties over CO2 production, saying that reduced output was the way to go. "As a nation, our first goal must certainly be to reduce emissions from all sectors, including agriculture," he suggests.
This is particularly true because it remains unclear whether we would be able to set our entire grassland carbon sink against carbon emissions.
Kyoto requires us to hold greenhouse gas emissions to 13 per cent above the 1990 level by 2008-2012, yet as of 2002 we are already running 20 per cent ahead of the 1990 output. Projections suggest we could hit 30 per cent of 1990 output by 2010, he says.