By becoming more energy efficient and streamlining day-to-day operations, it reduced its carbon dioxide (CO2) emissions, and offset its remaining emissions for the year 2017-2018 with help from its major partner EnergyAustralia. To reduce its carbon footprint, Australia's most recognisable building invested in renewables, tree planting and biodiversity projects to offset its greenhouse emissions. The 2015 Paris Agreement set a goal of limiting a rise in world surface temperatures, and last month the mayors of 19 cities, including Sydney, put in place regulations requiring all new buildings to be carbon neutral by 2030 and all existing ones to reach the same goal by 2050.

Each year the Opera House hosts 1800 events, serves 2.6 million food and beverage orders – producing 5000 cubic metres of waste and uses electricity equivalent to 2500 households (16 gigawatts). A new waste management program, including the introduction of new recycling streams and transferring food waste that would have otherwise gone to landfill to an organics facility to be turned into energy last year, improved the waste recycling rate from 25 per cent to 60 per cent. An educational program on waste management for staff and contractors also helped reduce waste.

"It’s the Opera House’s responsibility to find innovative solutions to reduce its carbon footprint and inspire the community to do the same," Opera House CEO Louise Herron said.

When designing the Opera House, Danish architect Jørn Utzon was inspired by nature
and integrated features now recognised as sustainable design which included an innovative seawater cooling system that continues to efficiently power the Opera House’s main heating and air-conditioning. An early interpretation of the "chilled ceiling" design (in wide use today to reduce energy consumption) remains in the Drama Theatre to help control the venue’s air temperature.

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The building was designed with durable materials to meet a 250-year lifespan, much more than the 80-year standard of the day. Utzon’s requirements for minimal finishings on building materials reduced resources used and maintenance requirements such as the white shell tiles of the sails which are self-cleaning.

The Sydney Opera House has also pioneered the use of green cleaning practices, rare for a public building, which include using baking soda for concrete cleaning, olive oil for bronze restoration, ozone-treated water for disinfectant, Lux soap flakes used in Western Foyers and a mixture of clay and Lux soap flakes used in the Uzton room.

“Sustainability is in the Opera House’s DNA," Ms Herron said.

"Architect Jørn Utzon incorporated sustainable design into the fabric of the building in the 1960s. We aim to honour and enhance this legacy by embedding sustainable thinking into everything we do. I’m proud to announce that thanks to long-term focus, creativity and the support of our partner EnergyAustralia we’ve become carbon neutral five years ahead of target," she said.

The next step in the Opera House’s Environmental Sustainability Plan (2017-2019) is to reduce its energy use by 20 per cent, achieve 85 per cent recycling of operational waste; achieve a 5-star Green Star Performance Rating (it is currently 4-star); and maintain its certified carbon neutral status year-on-year in time for its 50th anniversary in 2023.

"By slashing energy use and ramping up recycling the Opera House has truly set the stage for others to follow," NSW Minister for Energy and Utilities and Minister for the Arts Don Harwin said.