Heads of government from the Group of 20 (G20) nations are flying to Glasgow from a summit in Rome, where they agreed "meaningful and effective" action to limit global warming.
However, no concrete commitments were made, to the dismay of hundreds of protesters in Brussels.
Along with action to limit the emission of greenhouse gases, leaders must also discuss commitments by rich countries to help finance the transition away from fossil fuels in poorer ones.
For retired teacher Veronique, governments must be prepared to be honest with voters, without seeking to be popular.
(FRENCH) "The expectations are huge. We want firm, concrete, speedy promises. The politicians need to have the courage to disappoint a part of the population," she said.
World leaders will kick start COP26 on Monday (November 1) with two days of speeches that could include some new emissions-cutting pledges, before technical negotiators lock horns over the rules of the 2015 Paris climate accord.