Jubilant crowds began bidding farewell to the hottest year on record Sunday, closing a turbulent 12 months marked by clever chatbots, climate crises, and wrenching wars in Gaza and Ukraine.

The world's population — now more than eight billion — will see out the old and usher in the new, with many hoping to shake the weight of high living costs and global tumult.

In Sydney, the self-proclaimed "New Year's capital of the world", more than a million partygoers packed the harbor foreshore, with city officials and police warning that all vantage points were full.

Sydneysiders gathered through the day at prominent sites, defying uncharacteristically dank weather, and they were not disappointed when the Harbour Bridge and other landmarks were garlanded in light and color by eight tonnes of fireworks.

Sydney's spectacular show lit the fuse in 2024, a year that will bring elections concerning half the world's population and a summer Olympiad celebrated in Paris.

The last 12 months brought "Barbiegeddon" at the box office, a proliferation of human-seeming artificial intelligence tools, and a world-first whole-eye transplant.

India outgrew China as the world's most populous country and then became the first nation to land a rocket on the dark side of the moon.

It was also the hottest year since records began in 1880, with a spate of climate-fuelled disasters striking from Australia to the Horn of Africa and the Amazon basin.

Fans bade adieu to "Queen of Rock 'n' Roll" Tina Turner, "Friends" actor Matthew Perry, hell-raising Anglo-Irish songsmith Shane MacGowan and master dystopian novelist Cormac McCarthy.

Rebuilding

Perhaps more than anything, 2023 will be remembered for war in the Middle East — for Hamas's brutal October 7 raids on southern Israel and Israel's ferocious reprisals.

The United Nations estimates that almost two million Gazans have been displaced since Israel's siege began — about 85 percent of the peacetime population.

With once-bustling Gaza City neighborhoods reduced to rubble, there were few places left to mark the new year — and fewer loved ones to celebrate with.

"It was a black year full of tragedies," said Abed Akkawi, who fled the city with his wife and three children. 

The 37-year-old, now living in a UN shelter in Rafah, southern Gaza, said the war had obliterated his house and killed his brother.

"God willing this war will end, the new year will be a better one, and we will be able to return to our homes and rebuild them, or even live in a tent on the rubble," he told AFP.   

There was also hope in Ukraine, where Russia's invasion grinds towards its second anniversary, and defiance in the face of a renewed assault from Moscow.

"Victory! We are waiting for it and believe that Ukraine will win," said Tetiana Shostka, 42, as air raid sirens blared in Kyiv.

Some in Vladimir Putin's Russia are also weary of the conflict.

"In the new year, I would like the war to end, a new president, and a return to normal life," said 55-year-old theatre decorator and Moscow resident Zoya Karpova.

In Rome, Pope Francis prayed for the victims of conflicts around the globe, citing  Ukrainians, Palestinians and Israelis, the people of Sudan, and the "martyred Rohingya" of Myanmar.

"At the end of a year, have the courage to ask how many lives have been torn apart in armed conflicts, how many deaths?" the 87-year-old pontiff said after his Angelus prayer in St Peter's Square.

"And how much destruction, how much suffering, how much poverty? Those who have an interest in these conflicts, listen to the voice of conscience."

Putin is already Russia's longest-tenured leader since Joseph Stalin and will again be on the ballot paper when Russians vote in March, although few expect the vote to be fully free or fair.

To the polls

Russia's is just one of several pivotal elections scheduled in 2024. 

The political fate of more than four billion people will be decided in contests that will shape Britain, the European Union, India, Indonesia, Mexico, South Africa, Venezuela, and a host of other nations.

But one election promises global consequences. 

In the United States, Democrat Joe Biden, aged 81, and Republican Donald Trump, aged 77, appear set to rerun their divisive 2020 presidential race in November.

As the incumbent, Biden has at times appeared to show his advancing age and even his supporters worry about the toll of another bruising four years in office.

But if there are worries about what a second Biden administration would look like, there are at least as many concerns about a return of Trump.

He faces prosecution on several counts and 2024 could determine whether the bombastic self-proclaimed billionaire goes to the Oval Office or to jail.