Pittsburgh, Pennsylvania was once known as an industrial city where the skies were blackened with emissions from the steel mills that drove the local economy. But when world leaders gather there September 24 and 25 for their economic summit, they will find a city that has moved to the fore in environmental and energy saving technology.
The G20 will open its summit in one of the most beautiful spots in Pittsburgh - a huge glass-enclosed public garden that is a source of civic pride.
"It is a very inspirational place, a peaceful place, a very serene place," said Richard Piancentini, executive director of Phipps Conservatory.
Piancentini says Phipps was chosen for more than its beauty.
"We also think Phipps was selected because of what it represents," he said. "It is a very good example of some of the things of transformation that we have seen take place in Pittsburgh right now."
They do not just grow plants at Phipps anymore. They grow innovation.
The latest addition to Phipps - a tropical forest - is believed to be the most energy efficient conservatory in the world.
The unique design provides for natural heating and cooling - including a unique system of vents and underground pipes to bring in fresh air.
"It is like getting free air conditioning," he said. "It is not using any electricity but it helps keep the whole space cooler."
The commitment to green technology is also evident in the city's convention center - the main summit venue - which has won awards for its environmentally-friendly construction and design.
All this is taking place in a city that was once a prime contributor to global warming.
At the height of the steel industry, Pittsburgh was shrouded in industrial pollution. Long time residents - like Joseph Sabino Mistick - say for years the only time you could see the sky was when the steelworkers were on strike.
"I remember during the 1959 strike - I was 10 years old at the time - and I walked onto the porch one day and I started shouting for my grandmother to come," he said. "When she got there she said 'what is wrong?' I said 'the sky is blue.' She said 'remember one thing, Josie, if there is no smoke in the sky, there is no bread on our table."
His family worked at the Edgar Thomson steel mill. It is still in operation, though in a scaled down fashion - a part of the region's past that survives.
Travel down the highway from the plant and you run into the future.
John Bucher is the president of Solar Power Industries - a company that produces silicon ingots and solar panels.
"There is a $100 million invested in this factory," he said. "And it is producing high-tech, high-volume solar cells."
Solar power is a growth industry in southwestern Pennsylvania. Bucker says the region in going green.
"In the old days they would say you could not even see in front of you or if you had a white shirt you would have to change it by the time you got to the office," he said. "Nowadays, it is very clean and I think the new technologies, the renewables and the new types of technology are what are driving the business here, keeping it alive."
The director of Phipps Conservatory says he hopes the G20 leaders are impressed with Pittsburgh's commitment to the environment and energy conservation.
"I would like them to be inspired to see that this can be done, we can live more 'sustainably' on this planet," said Piancentini.
It is a message that would have seemed out of place in the Pittsburgh of the past, but is right at home today.