World leaders are gathered at the United Nations Headquarters in New York to sign a global climate change accord.
UN Secretary-General Ban Ki-moon said at least 171 countries are signing the deal, which was negotiated in Paris last December.
The accord’s central goal is to keep global temperatures from rising more than 2 degrees Celsius above pre-industrial levels.
The agreement will enter into force after 55 countries — representing 55 percent of global emissions — formally ratify it.
Many analysts are optimistic that could happen before 20-20, the date originally planned.