Ryanair has published its monthly carbon dioxide emission statistics, which it says is almost half the rate of other big European airlines.

The airline claims to be the first EU airline to publish monthly emissions.

The figures point to an average emission of 66 grams of CO2 per passenger per kilometre in the month of May.

It says this is substantially lower than its EU competitors.

Ryanair says it's committed to reducing this further to under 60g per passenger per kilometre by 2030, as outlined in its Environmental Policy.

The airline says its carbon dioxide emissions have already been cut from 82 grams a decade ago.

"As part of Ryanair's environmental commitment, we will invest over US$20 billion in a fleet of 210 new Boeing 737 "gamechanger" aircraft, which will carry 4% more passengers but reduce fuel burn by 16% and cut noise emissions by 40%," Kenny Jacobs, Ryanair's chief marketing officer said.

Meanwhile, the airline reported that it carried over 14 million passengers in May, a 13% increase on the figure for the same month last year.

Ryanair operated close to 78,000 scheduled flights in the month.

For the first five months of the year, the airline carried 132.1 million passengers, a 10% increase on the same period last year.