The growing popularity of larger cars and sports utility vehicles (SUVs) among drivers is now one of the single biggest contributors to increasing greenhouse gas emissions from transport in Ireland, new research has suggested.
The purchase of heavier, less fuel-efficient cars with larger engine sizes has eroded the fuel efficiency developments by car manufacturers in the last four years.
Some SUVs produce more than three times the amount of greenhouse gases when compared with smaller cars.
A report, submitted to the Government last week, estimates that this trend will add an additional 300,000 tonnes of greenhouse gases into the atmosphere each year.
This increase could cost the State between €15 and €75 million in levies under the Kyoto protocol on greenhouse gas emissions.
The report, by ICF consultants Byrne Ó Cléirigh engineering consultants, identified the trend as a significant element in recent emissions increases.
While the number of private vehicles in Ireland had increased by 90 per cent to 1.51 million, emissions from transport rose by 139 per cent.
The experts said that, despite trends improving internationally, fuel efficiency in the Irish car fleet had remained "virtually static" and was getting slightly worse because people were buying larger cars.
The report revised upwards greenhouse gas emissions by 300,000 tonnes as a result of the number of larger cars and warned that the amount could be higher if the current trend continued.
It cited research by Sustainable Energy Ireland, the State energy agency, which showed that the average Irish car is now less fuel efficient than in 2004, burning on average seven litres of petrol for every 100 kilometres travelled.
SEI also reported that the number of large cars, or private vehicles with engine sizes of more than 1900cc, had increased threefold since 1990 to nearly 200,000. There are now nearly 150,000 cars with an engine size of between 1700cc and 1900cc - more than five times the number in 1990.
Car manufacturers are required under European law to provide figures on fuel efficiencies and greenhouse gas emissions. These show that some SUVs and sports cars produce more than three times the amount of greenhouse gases for every kilometre driven, compared with the most fuel efficient smaller cars.
Some of the highest emission rates come from Land Rover and Range-Rover vehicles, with one Land Rover Discover model producing one tonne of CO2 emissions for every 2,518 kilometres travelled.
According to the latest figures from the Society of the Irish Motor Industry, the most energy efficient petrol cars available at present are the Daihatsu Charade 1 litre and the Opel Corsa 1 litre, which produce one tonne of greenhouse gases for every 8,700 kilometres travelled.