Today, 98 percent of all houses in Copenhagen are linked to the district heating system, according to the mayor.

"It gives better air quality, and it is much cheaper for Copenhageners to heat their apartments today than it was 25 years ago," Jensen said.

"It is not only a possibility to go green, it is also a must because we cannot continue conflicting with the climate. We must admit that we are living in a way that CO2 gives us a bad climate situation," he stressed.

Jensen said he is very optimistic about the outcome of the Paris climate conference, which aims to achieve a new international agreement on climate change, applicable to all, to keep global warming below 2 Celsius degrees.

"I think the world leaders have realized that it is now or never to make a climate agreement, which will prevent our planet temperature from rising over 2 degrees."

He said big nations like China and the United States will play a very big role in the climate negotiations.

"If the two nations, China and the United States, go in the front, it will be possible to reach an international agreement, because they will take the rest of the world with them," Jensen said.

KNOWLEDGE SHARING AMONG CITIES

For the first time in the upcoming Paris climate conference, cities are recognized by the United Nations for their work in combating climate change.

Jensen said cities around the globe should step up collaboration and cooperation to share knowledge, technologies and solutions for a better climate.

He cited the two cities of Copenhagen and Beijing as an example, noting that Beijing is trying to learn from Copenhagen about its advanced drinking water management as well as the district heating system, while Copenhagen is testing electric buses from Beijing in its own public transport system.

Copenhagen and Beijing have witnessed a closer relationship and intensified cooperation since they became "sister cities" in 2012, Jensen said.

"That is how cities can learn from each other. We don't have to innovate the same way in every city, but we can learn from others by sharing ideas, visions and concrete solutions," he said.