PARIS, Sept. 17 -- Global warming would be more severe than expected by 2100 unless governments take concrete moves to cut greenhouse gas emissions, French scientists warned on Tuesday.

By 2100, global mercury rise would reach 6 to 7 degrees Celsius due to "rapid economic growth driven by fossil fuels", experts from the National Center for Scientific Researches, Alternative Energies and Atomic Energy Commission (CEA) and weather agency Meteo France warned.

"Only one of the socio-economic scenarios (marked by strong international cooperation and giving priority to sustainable development) enables temperatures to remain below the 2 degree Celsius global warming target," they said.

They recommended "very significant mitigation efforts" to immediately cut greenhouse gas emissions to reach carbon neutrality over the globe by 2060.

"The intensity and frequency of heatwaves have increased in recent decades. This trend will continue for at least the next two decades, regardless of the scenario considered," they noted.

In France, two separate heatwaves this summer, in June and July, had brought record-breaking temperatures to the country's most regions, with temperature of 46 degrees Celsius recorded in the south on June 28.

The unseasonably hot weather caused 1,500 more deaths than usual in the country, according to official data.