It sounds like a tall order for just a simple roof, but a roof can either reflect the sun's heat back into the atmosphere, or it can absorb the heat and make the city even hotter.
'Cool roofs' are painted a light colour so they reflect heat, helping to keep the building below cooler.
Imagine deciding what to wear on a hot day. Wearing a white T-shirt will keep you cooler than if you wore a black T-shirt because it reflects more sunlight and absorbs less heat.
Cool roofs are like a white T-shirt, keeping the internal building temperature lower. That means less air conditioning, which saves energy and money.
Roofs and roads cover up to 65 per cent of urban areas and both are normally dark, making them absorb large amounts of heat.
This causes an 'urban heat island effect', where a city is warmer than its surrounding rural areas.
Cool roofs reduce the heat island effect and improve air quality by reducing emissions. One study found that using cool roofs and cool pavements in cities around the world could potentially cancel out the heating effect of up to two years of worldwide carbon dioxide emissions.
In the US capital of Washington DC, the government is changing the roofs of several government buildings in order to save energy in this way.
Some of the buildings, like the White House, already have light coloured roofs, but others need to be changed.
One government department installed more than 2 million sq ft of cool roofs on its offices across the country, which reduced its heating and cooling costs by 70 per cent.
This has saved taxpayers an average of US$500,000 a year in energy costs.
All new government buildings will have cool roofs from now on. The government hopes that by demonstrating the benefits of cool roofs on its own buildings, other Americans will follow the lead and adopt more sustainable building practices.
Cool roofs are one of the quickest and lowest cost ways we can reduce our global carbon emissions and help slow climate change. What colour is your roof?