Looking out of an aircraft window as you approach Sydney Airport or Melbourne's Tullamarine, our cities look clean, green, pollution-free. Solar panels wink back at you from a growing number of roofs.
But the simple fact is they are more dependent now on coal than they ever were in the depths of the Industrial Revolution. It's just that the energy generators are hidden away in the hinterlands, feeding vast amounts of power to the cities through high voltage cables and pumping out invisible CO2. It is the coal from Gippsland or the Hunter Valley that keeps the bright lights on in St Kilda and Kings Cross.
Here's a sobering thought for renewable energy campaigners: if every suitable rooftop in Melbourne or Sydney was crammed with the most high-tech solar panels available, and every tall building sprouted a wind turbine on its roof, the impact on the city's carbon footprint would be relatively small.
In the most detailed study of its kind ever undertaken, the City of Sydney worked out that if all suitable roof spaces in the inner city were fitted with solar panels - about 7.3 per cent of total roof space, a 350-fold increase in the amount of solar now deployed - it would account for only about 18 per cent of the inner city's electricity needs.
So is it possible for a modern, industrialised metropolis such as Melbourne or Sydney to be run solely off renewable energy, at a realistic cost? The answer is yes, but the journey to get there would require decisive change - in effect, another Industrial Revolution.
The impetus for change has intensified in recent months. The International Energy Agency, the World Bank and Australia's own Climate Change Commission have all issued clear-cut warnings about the risks of depending on coal as a primary energy source.
As green campaigners and some politicians urge people to take their superannuation investments out of coal companies, the climate commission put its weight behind calls for 80 per cent of known coal reserves to stay in the ground.
The Australian Coal Association and other groups representing the mining industries say the risks of coal investment are already factored in to the valuation of corporations.
But this week, US President Barack Obama added a powerful voice to the push away from coal, pledging to force coal-burning power plants to limit their greenhouse gas emissions, slashing fossil fuel subsidies in the United States and urging governments to get their money out of the coal industry.
''Today, I'm calling for an end of public financing for new coal plants overseas unless they deploy carbon-capture technologies, or there's no other viable way for the poorest countries to generate electricity,'' he said in a landmark speech on Tuesday. ''And I urge other countries to join this effort.''
With its cities unusually dependant on fossil fuels, by world standards, Australia is a test case for a transition to renewable energy.
The search for modern cities that are making the transition to genuine energy sustainability usually begins in Europe, where some cities in Scandinavia and Germany now run their energy grids completely free of coal.
But a more direct comparison to Australia's cities is found on the US west coast.
San Francisco has pursued an aggressive program of installing renewable energy on its municipal buildings and is well down the path of switching from being a fossil-fuelled city to a renewable one. ''The city was one of the first to set a goal of fulfilling 100 per cent of the city's electricity needs through renewable energy,'' says Conor Riffle, the head of the cities program with international non-government group the Carbon Disclosure Project.
''Overall, 41 per cent of San Francisco's electricity already comes from renewable energy, including large hydro, and the city is aiming to move this up to 100 per cent by 2020 without using new large hydro.''
This month, the Carbon Disclosure Project released a major study of 110 cities around the world in an effort to share lessons learnt about switching away from fossil fuels. Of those, 88 cities reported facing physical threats from climate change, particularly - given that most major cities are on waterways - from the risk of floods and sea level rise.
The key findings, though, were economic. Nine of every 10 cities surveyed thought their efforts to reduce greenhouse gas emissions would be good for business, creating more employment and opportunities.
''One out of every two actions that cities are taking to reduce emissions in their municipal operations is focused on efficiency,'' the report concludes. ''Cities report over $US40 million in savings per year from tackling climate change.''
As well as being potentially wealthier, residents in cities that are weaning themselves off fossil fuels tend to be healthier, the report found. ''The analysis shows that more than three-quarters (77 per cent) of reporting cities are undertaking actions to adapt to climate change that will also protect life and health,'' the report said. Straightforward benefits such as less air and water pollution, more walking and bike riding, sprang from attempts to reduce carbon emissions.
The simple act of planting and maintaining trees also has small but measurable effects, keeping temperatures down and absorbing air pollution from traffic.
In a world-first study of health effects of urban trees, the US Forest Service was able to show that, statistically, the simple presence of trees would save one life a year in a city the size of Melbourne or Sydney. In New York City, urban trees absorb enough particle pollution to prevent eight deaths a year from respiratory illness.
''Simply put, our urban forests improve people's lives,'' said US Forest Service spokesman Michael Rains.
But riding bikes and planting trees, though useful contributions in themselves, will not tackle the core problem of mass scale energy transition.
''Cities in many countries have effectively 'gone it alone' on climate change and sustainability for the last decade, as national governments have fallen asleep at the wheel,'' Riffle says. ''But realistically, to get the reductions we need, and to truly power their cities with renewable energy, it is nearly impossible for cities to go it alone.''
For that, city authorities need to find a way to work together with state and national governments. At this stage, that level of co-operation is rarely seen in Australia.
In Melbourne and Sydney, city councils are attempting to grapple with that problem by lobbying to loosen energy market regulations so smaller scale power generation can be shared between city blocks, allowing low-emissions power plants to power a portion of a suburb.
The Australian Energy Market Operator, which operates the national grid, is examining some of the regulatory issues, and is expected to publish a report on potential reforms to the energy market this year.
If small and medium scale energy plants are permitted to share energy, it would mark a sea change in the way power is distributed.
One effect would be the return of power generation to the heart of Australia's cities.
The City of Sydney lost face earlier this month, when it was forced to shelve plans for a trigeneration network - which would simultaneously produce electricity, heat and cold - in the city's Green Square precinct.
The miniature and highly efficient gas-fired power plants envisaged for the suburb are now on hold after the preferred tenderer for the contract, a subsidiary of Origin Energy, was unable to deliver the proposed level of carbon abatement within the city council's budget.
However, trigeneration is still going ahead in several of the city's buildings, as it is in cities around the country and the world. At present, it provides the simplest, cheapest known solution to making a city completely free of fossil fuels, because the plants can also burn biogas.
Biogas is the great and largely untapped energy resource that offers the simplest transition away from coal.
It is synthesised from biomass, or anything organic that decomposes - typically crop husks, wood offcuts, animal dung, and sewage. Put simply, our cities could be run on a resource that they will never run short of - our waste.
The City of Sydney surveyed every potential source of renewable gases within a 250-kilometre radius of the Central Business District. After scouring hundreds of piggeries, waste dumps and forestry sites, it was able to show that there is more than enough decomposing matter within easy reach of the existing natural gas pipe network to disconnect the central city from the coal-fired power grid. Melbourne, with even more farmland close to its centre, is thought to have greater resources.
'There is easily enough around Sydney, and it is readily accessible'' says Allan Jones, the City of Sydney's renewable energy adviser. ''The research shows that you can go to 100 per cent renewable energy this way.''
In Germany, the average farmer now makes 10 per cent of his or her cash income from selling biogas to that nation's power network, Jones says. On the council's calculations, an Australian farmer living within 200 kilometres of a major city could produce gas at roughly the same price as coal seam gas drilling companies currently do. Large-scale solar power plants, wind and wave energy would supplement a biogas-powered city network.
The total estimated capital cost of the council's project to run Sydney's inner city on biogas is $340.7 million, in today's dollars, between now and 2030. The cost of powering the whole city is unknown, but perhaps 20 times higher.
''The renewable energy resources and technologies to deliver both are available today and are being deployed in advanced economies around the world,'' the council's plan says.
''The issue for Australia is not that these renewable energy resources and technologies cannot be deployed in Australia but that the current narrow view and mindset … has to change if Australia is to become a renewable energy economy and potentially a major exporter of renewable energy.''