New Delhi: Energy is the most important issue confronting the world in the 21st century and even fast developing economies like India cannot grow without supply of cheap affordable energy, Director General for United Nations Industrial Development Organization said here.

"Today the reality is that we are living in an age of planetary boundaries. We cannot keep growing by continuing to do the things the same way. We cannot continue to pollute as much as we do, and especially using natural resources for energy", Kandeh K Yumkella said.

"You cannot solve climate change without energy revolution," stressed Yumkella, who was speaking at the 12th Delhi Sustainable Development Summit organised by the Energy and Resources Institute (TERI).

Quoting a McKinsey report, he said that in the next twenty years we will have three billion people moving into the middle class including many from India.

Yumkella said that as per the report these new middle class will want more of everything and the age of cheap food and cheap electricity and cheap other things would be over.

He said that "energy was the real basis for improving livelihoods."

"The reality is that in 2000 when we declared our energy development goals and our world leaders adopted them, there was no mention of energy. Energy was not an issue then," Yumkella said.

He said that in order to spur economic growth, address global inequities and preserve the environment, UN Secretary General Ban Ki Moon had established the Sustainable Energy for all Initiative.

"60 to 70 percent of green house emissions come from energy related activities," Yumkella said and added that connecting energy and climate concerns was very important and cannot be discussed in isolation.

He said that the United Nations was trying to bring awareness by connecting with diplomats and CEOs of big companies.

Yumkella also said that UN was taking initiatives so that the basic energy requirements of people in the less developed countries are also met. He spelled out three energy related targets that the UN had set.

"We've declared three targets. To achieve universal access of energy by 2030. To improve energy efficiency by 40 percent by 2030," Yumkella said.

"The third goal which is a bit challenging is to see if we can double our share of renewable in the global energy architecture," he said.