Here's what to know:

- Why it matters -

China is the world's second biggest economy, and since 2006, the largest polluter, now accounting for nearly 30 percent of global emissions. Paradoxically, it is also a clean energy powerhouse, rapidly shifting to renewable energy while selling the world its solar panels, batteries and electric cars.

Beijing's trajectory will be crucial to whether the world can limit end-of-century warming to 1.5C, the threshold UN scientists say is needed to avoid the most catastrophic impacts of climate disruption.

Under the Paris Agreement, countries must update their "Nationally Determined Contributions" every five years. With the year's main climate summit in Brazil fast approaching in November, expectations were running high for President Xi Jinping's announcement Wednesday at the United Nations.

China's 2021 pledge was to peak carbon dioxide emissions before 2030 and reach carbon neutrality by 2060. But it lacked near-term numerical targets, frustrating international observers.

The geopolitical context has raised the stakes: the United States has again quit the Paris accord under Donald Trump, who dismisses climate change as a "con job," while a fractious European Union has yet to set a new target.

- What it says -

Under the new plan, China pledges to:

- Cut economy-wide net greenhouse gas emissions by 7-10 percent from peak levels while "striving to do better." Some observers believe China's emissions have already peaked. Analysts note that to align with 1.5C, Beijing would need to slash emissions by about 30 percent within a decade from 2023 levels.

For context, the United States reached its peak of CO2 emissions in 2007 and reduced them by approximately 14.7 percent a decade later.

- Raise the share of non-fossil fuels in total energy consumption to over 30 percent and expand wind and solar capacity to more than six times 2020 levels, reaching 3,600 gigawatts.

- Increase forest cover to over 24 billion cubic meters.

- Make electric vehicles the "mainstream in the sales of new vehicles."

- Expand the national carbon trading scheme to cover high-emission sectors and establish a "climate adaptive society."

- What experts think -

Observers almost universally say the targets are too modest -- but that China is likely to surpass them thanks to its booming clean technology sector.

"This 2035 target offers little assurance to keep our planet safe, but what's hopeful is that the actual decarbonization of China's economy is likely to exceed its target on paper," said Yao Zhe of Greenpeace East Asia.

The decision to use an unspecified "peak" rather than set a baseline year for emissions cuts also raises issues, said Lauri Myllyvirta, lead analyst at the Centre for Research on Energy and Clear Air.

It keeps "the door open to near-term increases in emissions," he said, calling the pledges "a floor, not a ceiling, for China's ambition."

Kate Logan and Li Shuo of the Asia Society highlighted the phrase "striving to do better."

"This phrasing at least sends an upward signal that Beijing is potentially open to revising its on-paper commitment based on actual progress," they wrote.