At 9 a.m. in Paris (3 a.m. ET), negotiators are expected to produce a document that details how global warming can be limited.
That proposal will be handed over to world leaders or their representatives for a vote later in the day.
Capping the increase in global average temperatures to 2 degrees Celsius (3.6 degrees Fahrenheit)
was organizers' key goal going into the 21st Conference of Parties, or COP21. That level of warming is measured as the average temperature increase since the industrial revolution.
If that temperature threshold is not reached, the result may be superdroughts, deadlier heat waves, mass extinctions of plants and animals, megafloods and rising seas that could wipe some island countries off the map. The only way to reach the threshold, scientists say, is to eliminate fossil fuels.
Despite those dire predictions, getting 195 nations to agree on anything is difficult.
"Obviously, nobody will get 100% of what they want," French Foreign Minister Laurent Fabius said Friday
as he discussed the "balanced and as ambitious as possible" working document that will be voted on. "What I hope is that everyone remembers the message of the first day, when 150 heads of state and government came from all around the world to say, 'The world needs a success.' "
Countries must agree by consensus. Organizers hope countries will adopt the proposal but there could be some nations that don't go along. It will be up to the COP21 president to decide whether there's an agreement.
After the vote in Paris, the countries that adopt the agreement will later have to ratify it nationally.
Negotiators took a key step last Saturday with the release of a draft agreement
that has been posted online by the United Nations Framework Convention on Climate Change
. That draft has been modified throughout the week.
Many officials have talked about the importance of doing something to slow the pace of global climate change. Having legally binding reductions in greenhouse gas emissions
has long been seen as a priority to make this happen.
One of the sticking points has been coming up with a way to punish nations that don't do their part.
For now, it appears parties are leaning toward mostly an honor system agreement, with individual countries making pledges that won't necessarily be enforced by any world court or body.
Other issues, according to observers:
Whether there would be reparations paid to countries that will see irreparable damage from climate change but have done almost nothing to cause it and how countries will have their pollution-reduction efforts monitored.