The world's mega cities and rural towns should invest in centralized energy systems to reduce fossil fuels consumption during cooling or heating in buildings, said a United Nations (UN) report launched on Friday.

According to the District Energy in Cities Report authored by the United Nations Development Program (UNDP), cities are responsible for 50 percent of green house gas emissions that can be reduced through a centralized system to heat and pipe water to households.

"Our ability to keep the world within a two degrees scenario has led us to focus on district energy in cities. This approach is practical, benefits consumers and will enhance our response to climate change," said UNDP Executive Director Achim Steiner.

He said the District Energy Systems that have been adopted in many cities globally focus on a centralized approach to pipe steam, hot or cold water in a bid to cut fossil fuels consumption.

The UN report noted that this system will boost energy efficiency, air quality, and savings in cities.

"We need to enlighten decision makers, mayors and leaders at community level on the importance of District Energy Systems to promote a transition to green," Steiner said.

The report said that district energy systems are the most cost effective way to reduce carbon emissions in cities.

"Cities are crucial partners in making sustainable energy for all a reality. Through adoption of energy efficient systems, cities can help mitigate impacts of climate change," said Kandeh Yumkella, CEO of UN Secretary General's Sustainable Energy for All Initiative.

Experts emphasized that modern and energy efficient heating and cooling systems in cities will cushion nations from economic shocks and extreme weather events, the UN official said.