Undaunted by terrorism, 40,000 diplomats, experts and advocates, including more than 135 world leaders, are set to meet in Paris beginning Nov. 30 for a major U.N. Climate Summit.

The goal is a new global climate treaty, involving all nations, that would enter force in the year 2020 and help the world avoid the worst consequences of manmade global warming.

During previous U.N. climate negotiations, world leaders agreed to limit global warming to at or below 2 degrees Celsius, or 3.6 degrees Fahrenheit, above preindustrial levels by the year 2100, determining that any warming beyond that would set in motion dangerous and potentially unstoppable climate impacts, from melting ice sheets to extreme and deadly heat waves.

We are already halfway to that target and closing in fast.

The meeting is widely viewed as the last chance for the world to limit global warming to the temperature target.