Sydney's skyline is greening and the city's big end of town has emerged as a global leader in emissions reductions.

The biggest portfolio of commercial buildings, representing half of the city's office spaces, has reduced emissions by 52 per cent in just seven years.

"It's just fantastic and they are saving $33 million annually," Lord Mayor Clover Moore told the ABC.

Ms Moore signed a pact with half of the city's building owners in 2011, with the goal of reducing emissions by 70 per cent by 2030.

The Better Building Partnerships (BBP), which has a portfolio worth $105 billion, is set to reach that goal years before the target date.

"We know that 70 to 80 per cent of emissions happen in our cities, so if we can get our emissions down in our cities we are making a great contribution to addressing climate change," the Lord Mayor said.

The council has reduced its emissions by 25 per cent. Across the CBD, the figure is closer to 19 per cent.

Ms Morre said there was potential for greater take-up of sustainability initiatives by other landlords in the entertainment and hospitality sectors, and there was progress in small businesses, and residential and mid-tier buildings.

Some of the big achievers in reducing emissions include the heritage-listed Number 5 Martin Place, which was restored with sustainability in mind by Dexus and Cbus Property.

BBP chairman and the head of sustainability at Dexus Paul Wall said getting it right during the construction phase was critical.

Much of the century-old Commonwealth Bank headquarters built on that site was been kept during the construction of a 14-storey tower.

If you look at the steel, we've avoided 5,000 tonnes in carbon emissions by not having to produce the steel that would have been needed to replace that building," Mr Wall said.

Meanwhile, Grosvenor Place, the Seidler-designed 44-storey office block which was opened in 1988, has been retrofitted.

There are 200 solar panels on the roof generating up to 3 per cent of the building's electricity needs, or enough to power the lighting in the common areas.

The rain that falls on the atrium roof is captured and recycled — flushing 100 toilets over 12 floors.

Responsible investing is in

The Global Real Estate Benchmark (GRESB), which assesses the environmental sustainability of buildings for international investors, rates Sydney as a strong performer.

"We are seeing that they are attracting more capital from other regions into Australia because they are showing that they are decreasing the footprint of their portfolio, which is increasingly important to investors who want to invest responsibly," GRESB head of of Asia-Pacific Ruben Langbroek said.

The EY Building at 200 George Street Sydney is rated one of Australia's most advanced and sustainable buildings.

A timber blind system with sensors manages the flow of heat and light in the building.

Natural lights fill the floors which are linked with internal staircases.

Builder Mirvac told the ABC the building has a "small rainwater capture and reuse system to reduce potable water consumption" and a "hybrid air-conditioning system incorporating active chilled beams and variable air volume units".

Mirvac boasts that 90 per cent of its construction materials were recycled and required minimal landfill, and that in its offices more than 80 per cent of waste was recycled.