Asle Sveen, a historian and author of several books about the prize, said Thunberg would be a strong candidate for this year's award, her second nomination in as many years, with the US West Coast wildfires and rising temperatures in the Arctic "leaving people in no doubt" about global warming.
"Not a single person has done more to get the world to focus on climate change than her," Sveen told Reuters. The committee has given the prize to environmentalists before, starting with Kenya's Wangari Maathai in 2004 for her campaign to plant 30 million trees across Africa, and in 2007 to Al Gore and the Intergovernmental Panel on Climate Change.
In the era of the coronavirus crisis, the committee could also choose to highlight the threat of pandemics to peace and security, said Dan Smith, the director of the Stockholm International Peace Research Institute.
"There is a relationship between environmental damage and our increasing problem with pandemics and I wonder whether the Nobel Peace Prize Committee might want to highlight that," he told Reuters.
If the committee wanted to highlight this trend, he said, "there is obviously the temptation of Greta Thunberg".
The Fridays for Future movement started in 2018 when Thunberg began a school strike in Sweden to push for action on climate. It has since become a global protest.
Thunberg and her father Svante, who sometimes handles media queries for her, did not reply to requests for comment.
Many were sceptical when Greta, as she is often referred to, became the bookmaker's favourite to win last year's Nobel Peace Prize, especially with regards to her age, but her second nomination could strengthen her chances.
The Irish betting agency Paddy Power has the World Health Organization (WHO) as its favourite at odds of 5/2, followed by Thunberg at 3/1 and New Zealand Prime Minister Jacinda Ardern at 5/1.
"Greta is re-nominated, which was the case for Malala. I said Malala was young when she was nominated the first time and I said Greta was young the first time she was nominated," Sveen said.
Yousafzai won in 2014.
Other known candidates included the "people of Hong Kong", NATO, Julian Assange, Chelsea Manning and Edward Snowden and jailed Saudi activist Loujain al-Hathloul.
Other possible choices are Reporters Without Borders, Angela Merkel and the WHO, experts said, though it is unclear whether they are nominated.
Nominations are secret for 50 years but those who nominate can choose to publicise their choices. Thousands of people are eligible to nominate, including members of parliaments and governments, university professors and past laureates.
It is not known whether Donald Trump is nominated for this year's prize, though he is up for next year's award after a Norwegian lawmaker named the US president for helping broker a deal between Israel and the United Arab Emirates.
He is unlikely to win, Sveen and Smith agreed, not least for his dismantling of the international treaties to limit the proliferation of nuclear weapons, a cause dear to Nobel committees.
"He is divisive and seems to not take a clear stance against the violence the right-wing perpetrates in the US," said Smith.