Moves to improve energy efficiency have allowed shipping giant Maersk Line to cut harmful air emissions, even amid a time of expansion.

The firm noted that changing its global network of shipping routes last year helped lower fuel costs and cut carbon dioxide emissions, reported Straits Times.

The Danish company also credits the four environmentally friendly Triple-E ships introduced last year for improving energy efficiency.

It will add 16 more to its fleet by 2015.

Maersk Line's 550 container vessels used 1.2 million tonnes less fuel last year than in 2012, a move that saved US$764 million and helped the company deliver a $1.5 billion profit in 2013.

The world's largest container shipping line also expanded its shipping volume by 4.1 percent last year compared with 2012 and cut its carbon dioxide emissions by 3.8 million tonnes over that same period.

Maersk Line also reduced its sulphur emissions by 67,000 tonnes – 12 percent – last year over 2012, mainly through switching to low-sulphur fuels like diesel. This allowed it to reduce its sulphur emissions in Singapore by 50 percent last year compared with 2012.

This resulted in a saving of 478 tonnes of sulphur emissions, which is equivalent to around half of all sulphur emissions from vehicles in Singapore.