Senior State Department officials said on Wednesday they were "optimistic" that a deal on cutting greenhouse gases used in refrigerators, air conditioners and aerosols can be struck during meetings in Rwanda this week. "We are optimistic about reaching an agreement," a senior State Department official said as U.S. Secretary of State John Kerry left to join negotiations in the Rwandan capital, Kigali. About 150 nations are meeting in Kigali from Oct. 10-14 to try to agree a phase down of factory-made hydrofluorocarbon (HFC) gases. A quick reduction of HFCs could be a big contribution to slow climate change, avoiding perhaps 0.5 degree Celsius (0.9 Fahrenheit) of a projected rise in average temperatures by 2100, scientists say. An HFC accord would be the third big step this month to curb global warming after the 2015 Paris Agreement and comes less than a month before the U.S. presidential election. India, in particular, has been under pressure to agree to speed up its plans for cutting HFC's. It wants a peak in poor nations' rising emissions only in 2031 to give industries time to adapt. The United States believes that India would negotiate in good faith during the Kigali talks, the U.S. official said, speaking on condition of anonymity. The official said Indian President Narendra Modi and U.S. President Barack Obama had committed in June to achieving a successful outcome of the Kigali talks. The HFC talks are part of the 1987 Montreal Protocol, which succeeded in cutting the use of chlorofluorocarbons to help protect the ozone layer, which shields the planet from ultraviolet rays that can cause skin cancer.