Delegates from nearly 200 countries are meeting in the Turkey's resort city of Antalya as global greenhouse gas emissions show little sign of falling and wars, inflation and other crises compete for political attention.
A UN report in October found the world on course to break through the 1.5 degrees Celsius warming limit that countries had agreed to pursue under the Paris Agreement to prevent the worst of climate change.
Former French Prime Minister Laurent Fabius, who presided over the 2015 Paris climate conference and leads an advisory council of former COP presidents, said the speeches could give political impetus to the negotiations.
"It is an opportunity for leaders to make some announcements, and more this time, to explain how they will implement, because the key word in Antalya is implementation," he told Reuters.
Scores of world leaders will begin their speeches on Wednesday and continue on Thursday.
Wednesday's speakers include Brazilian President Luiz Inacio Lula da Silva, who was re-elected at the end of October, and whose country hosted last year's climate talks.
European Commission President Ursula von der Leyen, Chinese Vice President Han Zheng, and Marshall Islands President Hilda Heine will also speak on Wednesday.
The United States, the world's largest historical emitter, has skipped the talks for the second year in a row after President Donald Trump - who has called global warming a hoax - withdrew the US from climate co-operation following his return to office in 2025.
COP31 host Turkey has so far been pushing the government representatives attending the conference to put a goal on electrification at the centre of a final deal, even as critics say it may do little to curb warming.
The proposal targets a rise in electricity's share of total global energy consumption to 35 per cent by 2035, up from a little over a fifth now, theoretically reducing greenhouse gas emissions from cars, factories, and buildings.
But the proposal does not include language requiring new power to be generated by clean energy sources, and world governments have yet to clarify a broader plan to transition away from fossil fuels like coal, oil and gas.
"It is long past time to stop treating the transition away from fossil fuels as taboo or intractable," UN Secretary-General Antonio Guterres told the conference, urging countries to produce clear timelines for the transition.
The previous COP in Brazil was unable to reach consensus on the need for a global plan to reduce dependency on fossil fuels.
