Negotiators from nearly 200 nations are in Germany to try to refine a deal that could save the planet from more extreme weather. The Bonn talks are a crucial step towards sealing a new global pact at the year end at major United Nations talks in Paris.
The UN says a deal to save the climate is vital if we are to limit how much the planet warms. Failure could condemn us to a future of deadlier heatwaves and wildfires, crop failures and dying coral reefs.
The negotiations, which end today, and another five-day round next month are the last chance before Paris for negotiators to narrow major differences on how best to limit greenhouse gas emissions that are heating up our world.
The talks are tough because they are fundamentally about fairness - who should cut emissions, by how much and by when. The talks are also about how economies use energy to power their growth. No nation wants to sign up to an unfair deal that could limit its economic growth.
Ultimately, ministers and heads of state will have to make hard political decisions in a bid to compromise, with much of the tough bargaining set for the Nov 30 to Dec 11 Paris talks.
Plenty of sticking points remain. Money is a top issue. Rich economies have already agreed to US$100 billion (S$140 billion) a year in financial support for poor countries, starting from 2020. But where that cash will come from, and how it will be distributed, still has to be worked out.
The Paris climate pact's ambition is another concern. Ahead of Paris, more than 50 nations have submitted their climate pledges, with more to come. Yet collectively, scientists say the pledges will not be enough to limit warming to 2 deg C - the goal.
Already, there are warning signs about the future. Last week, the National Aeronautics and Space Administration said 1m or more of sea-level rise is unavoidable in the next 100 to 200 years. Scientists say 2015 is likely to be the hottest year, beating 2014.
The negotiations in Bonn and a deal in Paris could be our best shot at bringing us back from the brink.