For 25-year-old Marcel Suttrup who lives in the northern German city of Hamburg, a typical day starts with energy-efficient lights and water drawn from taps with flow-thinning adapters.

As a freelance worker for events, Suttrup tries to live a life with less use of household appliances and more resort to public transport.

"I think this is important. The world is challenged by climate change," he said. Nowadays, Suttrup is only one of the many in Hamburg, or even Europe at large, who are contributing to the " green" cause.

Taking buses or subway trains is a common practice in the city where an inclusive public transport network integrates all inner- city trains and buses -- passengers could buy a monthly ticket priced at around 90 euros and choose the means of transport as they like.

Around 1,000 rental bikes are available in stops throughout the city with free rides for the first 30 minutes. Statistics show that about 16 percent of current daily mobility in Hamburg is by bike and the figure is projected to rise to 18 percent by 2015.

Besides, almost 17 percent of the urban region is made up of public parks, recreation areas and woodlands. Some 200,000 energy- saving lamps in public buildings help reduce millions of euros in cost per year.

In 2009, the European Commission awarded Hamburg the title of " European Green Capital 2011" for its outstanding performances in combating climate change, as well as in waste-water management and local governance.

Janez Potocnik, European Commissioner for the Environment, said, "The European Green Capital Award is one of the ways we can promote better sustainable mobility, modern waste management, sustainable land use, and green solutions, which local authorities can use for themselves."

He believes that most of the environmental challenges today originate in cities, which is worrying because around 75 percent of Europeans live in cities.

European Commission rules stipulate that cities winning the title of "European Green Capital" must have ambitious goals for improvement.

And part of Hamburg's response to that is to cut its carbon dioxide emissions by 40 percent by 2020 and 80 percent by 2050.

Various events to that effect are taking place in Hamburg, including congresses and exhibitions for energy saving, water consumption, and environmental conventions.

The "Train of Ideas," as rolling ambassador for the city of the future, began its journey in April 2011. Departing from Hamburg, the train embarked on a tour throughout Europe, visiting a total of 18 European cities and presenting its urban environment exhibitions on the road.

Britta Kastens, communications officer for the European Green Capital project in Hamburg, said winning the title was not easy because as a traditionally industrial port city, Hamburg had real environmental problems.

Home to a population of 4.3 million in the metropolitan region and 1.8 million in the city, Hamburg has more than 300,000 commuters each day and hosts above 500 industrial firms. It is also the third largest port in Europe, able to handle large ocean- going vessels.

In the early 20th century, the skies of Hamburg used to be shrouded by clouds. And that changed only after 1960, when coal was substituted mainly by gas and nuclear power as the primary energy source in Hamburg.

In the 1970s, noise pollution from industry, ground and air traffic became a nuisance, provoking citizens to protest and take the issue to court.

In 2008, Hamburg's Senate decided to build a super roofing structure to cover large sections of a main motorway in an effort to reduce noise.

Even now, according to Kastens, Hamburg still faces environmental challenges.

Manufacturing companies in the city employ some 83,000 people, primarily in aircraft and spacecraft engineering, as well as in Europe's largest copper smelting plant, which is no more than two kilometers from the city hall.

Meanwhile, with the number of per capita millionaires higher than any other city in Europe, the streets of Hamburg are frequented by sports cars all day long. In 2010, around 133,000 cars were newly registered here and each family now has an average of two to three cars.

To Suttrup, this is a problem. "Many people still do not care about living green," he said. "It's not fair that some of us are trying to save energy but others are throwing it about."

At the national level, said a report of the German Association of Energy and Water Industries, for the first time, renewable sources accounted for more than 20 percent of the country's electricity generation in the first half of 2011.

But questions remain as to how Germany would fill up the energy hole vacated by nuclear power since the government bowed to public pressure in May this year and announced plans to shut down the country's 17 nuclear power plants by 2021.

Jens Kerstan, chair of the Parliamentary Green Party in Hamburg, said the city might need to buy power from other federal states or countries.

But in general, he is optimistic and said the green campaigns will possibly go faster. "Of course technology is the most important in resolving energy issues in the future and that needs a lot of investment. But I think it's totally worth it."