Ryanair boss Michael O'Leary has hit back at criticism from the climate change minister, saying his airline was "the greenest in Europe".
In a broad attack on airlines' efforts to tackle carbon emissions, Ian Pearson said Ryanair was the "irresponsible face of capitalism".
But Mr O'Leary said Mr Pearson was "silly" and "hadn't a clue what he is talking about".
Mr Pearson also said the attitude of US airlines to emissions was "a disgrace".
In an interview with the Guardian, Mr Pearson said: "When it comes to climate change, Ryanair are not just the unacceptable face of capitalism, they are the irresponsible face of capitalism."
He also attacked British Airways, saying it was "only just playing ball" on environmental regulations, and Lufthansa, the German airline.