UNITED NATIONS-Paris Mayor Anne Hidalgo urged the world's major cities Thursday to unite in the fight against climate change . Stressing that half the world's population is now urbanized, she noted that cities are already responsible for 80 percent of greenhouse gas emissions and the consumption of three quarters of Earth's energy resources. ‘Major cities must unite to develop industrial bids to tackle concretely the dangers of climate change and the massive loss of biodiversity,’ Hidalgo said. She spoke during a sustainable urbanization conference at UN headquarters in New York. Paris will host a major UN climate conference at the end of 2015, when the world's nations are due to sign a global climate pact. Meanwhile, it is ‘very important that major cities get together and commit to sharing best practices as part of a dialogue to speed up the ecological transition of our economies,’ Hidalgo said. She pointed to a public housing building in Paris ‘heated for free’ by energy generated by computer microprocessors performing calculations. The French capital is focusing on pushing green construction norms ‘very far’ for new buildings and on non-polluting public transportation,’ Hidalgo added.