More than 100 heads of government and 40,000 other attendees are meeting on Nov. 30 for the launch of the two-week United Nations conference on climate change. Negotiators expect the gathering, formally known as the 21st Conference of Parties (COP 21) to the United Nations Framework Convention on Climate Change (UNFCCC), to yield the most significant international agreement yet to reduce global greenhouse gas emissions, and slow the effect of climate change.