Choi Hee-woo (left) became one the world's youngest plaintiffs when his mother, Lee Dong-hyun, (right) signed him up as the plaintiff in a climate lawsuit while he was still in utero. (AFP)

When he was a 20-week-old embryo -- before he even had a real name -- Choi Hee-woo became one of the world's youngest-ever plaintiffs by joining a groundbreaking climate lawsuit against South Korea.

His case, known as "Woodpecker et al. vs. South Korea" after Choi's in utero nickname, seeks to prove Seoul's modest climate goals -- reducing carbon emissions by 40 percent of 2018 levels by 2030 -- are a violation of their constitutionally guaranteed human rights.

In Asia's first such climate case -- a similar youth-led effort recently succeeded in the US state of Montana, another is ongoing at the European Higher Court -- the plaintiffs claim South Korea's legally binding climate commitments are insufficient and unmet.

"I had no idea an embryo could participate," Choi's mother, Lee Dong-hyun, told AFP, adding that she'd been planning to sign up Choi's older sibling before realizing her unborn child could also become a plaintiff.

Choi or "Woodpecker" -- his parents heard the bird's call after learning they were pregnant, Lee said -- is the youngest of the 62 children involved, although most were under five when the suit was first filed in 2022.

Lee is confident the court will rule with the children -- which could force revisions to Seoul's climate laws, although the scale of any potential changes is not clear.

"Considering the future of humanity, it's obvious the government should make more active efforts to ensure our survival amid the climate crisis," she said.

"I would be so sorry if my children never experienced a beautiful spring day," she said ahead of the final hearing this week of four climate cases, which for procedural reasons were merged into one, at South Korea's Constitutional Court.

Youth climate activist Kim Seo-gyeong, 21, was part of the group that filed the first of the cases in 2020. She said it was taking too long for the government to address young people's demands, as their legal challenge makes its way through the courts.

"Four years might not seem too long for a constitutional appeal, but it is too significant for a climate crisis," she said.

"For the decision makers, it still isn't enough of a crisis to compel action."

In 2021, South Korea made a legally binding commitment to reduce carbon emissions by 290 million tons by 2030 -- and to achieve net-zero carbon emissions by 2050.

In order to meet this goal, the country needs to reduce emissions by 5.4 percent every year from 2023 -- a target they have so far failed to meet.

It's highly unlikely Seoul will meet its official climate goals, said Noh Dong-woon, a professor at Hanyang University in Seoul. "With the current administration's industrial-friendly policies and South Korea's heavy industry structure, we should have done something much sooner," he told AFP.

In 2022, South Korea generated just 5.4 percent of its energy from wind and solar, less than half the global average of 12 percent, and far behind neighboring Japan and China, energy think tank Ember said, adding the country is also the G20's second-highest carbon emitter per capita.

"If South Korea doesn't look to renewable electricity to power manufacturing, it risks losing market share" as more blocs like the European Union move to penalize imports from heavy polluters, Helen Clarkson, CEO of Climate Group, told AFP.

Similar climate litigations globally have found success, for example, in Germany in 2021, where climate targets were ruled insufficient and unconstitutional.

But a child-led suit in California over alleged government failures to curb pollution was thrown out earlier this month.

For 12-year-old plaintiff Han Je-ah, who loves K-pop idols, dancing and climate activism, adults are not taking the climate crisis seriously enough, because it won't ultimately affect them.

"When the Earth's temperature rises two degrees Celsius more, none of the adults who are talking about this right now will still be around -- even President (Yoon Suk Yeol)," she told AFP.

"The children left behind will be responsible for reducing carbon emissions and suffer the consequences."

Je-ah, who said she would like to be a professional gamer, soldier or a farmer when she grows up, delivered a statement during the final hearing Tuesday.

"It is absolutely not fair to ask us to solve the problem. If the future is worse than it is now, we may have to give up everything we dream of," she told the court.

Her lawyer, Youn Se-jong, told AFP the youthful nature of the plaintiffs helped hammer home people's "desperation for change." "And I am hopeful we will win," he added.