BERLIN (AP) — The head of the United Nations scientific panel on climate change urged diplomats and scientists to show “enlightenment” Monday, as they began a weeklong meeting aimed at spelling out in plain terms what options the world has if it wants to prevent catastrophic global warming.

Delegates at the closed-doors meeting in Berlin need to tackle a number of sensitive issues, including how best to cut carbon emissions and how to share the cost of shifting away from the fossil fuels that are largely blamed for producing the gases that are heating the planet. Their conclusions will feed into a landmark assessment report that will form the basis of negotiations for future climate treaties.