The European Commission has awarded the title of "European Green Capital" for the year 2017 to Essen, in western Germany.

Every year, the award showcases achievements in environmental sustainability, including local efforts to improve the urban environment and promote sustainable growth. Since 2010, the title is granted to one European city with a population of more than 100,000 each year. Winners are announced two years in advance.

In this year's contest to select the 2017 winner, 's-Hertogenbosch and Nijmegen in the Netherlands and Umea in Sweden were also shortlisted from 12 entries across Europe.

Essen, a former coal-mining city in the heart of the Ruhr region, was particularly recognized for overcoming its challenging industrial history to reinvent itself as green, thus becoming a leading example for other cities.

For 2016, the winner was Ljubljana in Slovenia. Bristol in the United Kingdom took the title for 2015, and Copenhagen won the previous year.

But what actually makes all these cities "green"?

Innovative climate solutions

For the contest, an "international and independent" panel of experts assessed applicant cities on key indicators including air quality, local transport, green urban areas - and how they are dealing with climate change.

George Ferguson, the mayor of Bristol, described climate change as the "biggest challenge" European cities face. Tackling this, he added, was about innovation - along with a sense of fun. Those two elements have come together in what is popularly known as Bristol's "poo bus."

Bristol Mayor George Ferguson says climate change must be tackled with innovation

"It's the bus number two, and it runs on human waste," Ferguson told DW. "It doesn't smell," he added.

The poo bus is part of Bristol's campaign to reduce its carbon footprint 40 percent by 2020. Other efforts towards this goal include support for projects that promote renewable energy and reduce energy consumption.

Making green fun

Lykke Leonardsen, head of Copenhagen's climate unit, echoed the sentiment that ingenious thinking must go hand-in-hand with "making it fun."

Copenhagen, Bristol's predecessor as the European Green Capital, has an even more ambitious climate goal: To be carbon-neutral by 2025. And over the past decade, Copenhageners have already reduced their carbon footprint by 40 percent.

This has come through efforts including building up renewable energy - and bicycling infrastructure. Such infrastructure is not necessarily physical.

Leonardsen described Copenhagen's "bike butler" program: When people park their bicycles in inconvenient spots, the butlers remove the bike. But when the cyclists come to pick up their ride, they're not punished with a fine, rather greeted with a friendly face - and their bike has a freshly oiled chain and pumped up tires.

"By creating elegant and beautiful solutions for people who are bicycling, it becomes much more attractive," Leonardsen told DW. "Then it's not seen as something I have to sacrifice - I do it because it's fun and it's cool."

Many cities - including Brussels, a green capital candidate for 2015 - have public bicycle rental services

And apparently, that's worked - because by now in Copenhagen, 45 percent of all trips to work and school are done by bicycle.

Green infrastructure

Beyond reducing its carbon footprint, a "green city" is also literally green. But that doesn't merely mean parks.

The new buzzword in urban planning is "green infrastructure" - broadly defined as natural areas designed to carry out a variety of functions.

Ronan Uhel of the European Environmental Agency described green infrastructure as "a nature-based solution" that can also contribute to preserving biodiversity.

"It can be related to the energy efficiency of buildings, it can mitigate the fragmentation of our landscapes, it can also be helpful in regenerating accessibility to rivers," he told DW.

One huge green infrastructure project in Copenhagen involved creating a network of green areas that can handle storm runoff - the result of a rethink from an unprecedented cloudburst in 2011 that caused massive damage to the city's infrastructure and put countless lives at risk.

Now, these green areas divert storm water, help clean the air, and act as gathering spaces for the community. "It's greening the city, making it healthier, making it more attractive," Leonardsen said.

Green urban spaces offer habitats for insects and animals, and a respite for humans

Link with economy

Martin Powell, head of urban development with Siemens corporation in the UK, underlined how important this is: "A green city is absolutely essential to attract the human capital you want working and living there."

Powell believes both cities and private developers can "piggyback" such green infrastructure onto investment. When major buildings undergo an energy retrofit, that can include green features, he told DW.

"Why don't you integrate this with a green roof, a permeable piazza outside to help surface water runoff, sustainable drainage and some other green infrastructure," Powell suggested.

'Laboratory for change'

Ferguson described cities as the source of "a lot of the problems and a lot of the solutions."

"The idea is if cities can become a laboratory for change, they can then spread the whole benefit across Europe," Ferguson said.

"One city alone is not going to change the world. But if we share these ideas, and we share our problems, and we share the answers, then we can change the world."