But behind the scenes, the airport has also been hard at work increasing its environmentally-friendly credentials, undertaking more than 10 projects in 2016 and 2017 to improve its energy efficiency.

These efforts helped Changi Airport achieve level three in the Airport Carbon Accreditation in May.

There are four levels of accreditation under the scheme, the first of which is for airports to measure their carbon footprint.

Level two requires that airports take steps to reduce their carbon output, while level three is for those that have also brought other service providers on board.

In Changi's case, ground handling firms such as Sats and Dnata, as well as its restaurants, are participating in green efforts.

The highest level - three plus - is for airports that have become carbon neutral, referring to the reduction or offsetting of their emissions to zero. This feat has been achieved by about 30 airports so far.

The accreditation program was set up by Airports Council International to encourage airports to reduce their carbon emissions.

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According to the International Air Transport Association, total carbon emission of the global aviation industry last yearwas about 859 million tonnes, or 2 per cent of all carbon emissions worldwide.

Among the efforts undertaken by Changi Airport was the overhauling of air-conditioning chillers in Terminals 1 and 2 to become more energy efficient in 2016.

This helped save some 5.56 million kilowatt hours (kWh) - the amount of electricity used by more than 14,000 four-room flats in a month - reducing carbon emissions by 2,355 tonnes that year.

Last year, floodlights at the aircraft parking bays of Terminals 1, 2 and 4 were replaced with more energy-efficient light-emitting diode (LED) alternatives, saving 1.52 million kWh.

In place of the more polluting diesel tractors, 80 electric-powered baggage tractors - which can be charged at 26 charging points across the airport - were introduced last year with the opening of Terminal 4.

Changi Airport Group business development director Gerald Ng said the moves are in line with the airport's commitment to "carry out our business activities in an environmentally responsible manner".

"We are continuously looking to improve our energy and water consumption, along with reducing waste generation and carbon emissions," he said.