China has published its long-awaited national plan on greenhouse gas emissions, just days before the opening of the Cop26 UN climate summit.

However, the plan revealed on Thursday represents little progress on the previously announced ambitions of the world’s biggest carbon emitter, disappointing observers of the vital climate talks.

Emissions would peak by 2030 and be reduced to net zero three decades later, according to the nationally determined contribution (NDC) submitted to the UN.

This is widely regarded as too late to ensure the world limits global heating to 1.5C above pre-industrial levels, which is the key aim of the talks.

The submission was sent by Li Gao, the director general of the department of climate change in the Chinese environment ministry, to Patricia Espinosa, the executive secretary of the UN framework convention on climate change.

Compared with China’s previous NDC in 2015, there is modest progress. The new document is clearer that China intends emissions to peak by 2030, with a reduction of the carbon intensity of the economy by more than 65%.

It raises the share of non-fossil fuels in primary energy consumption to 25% from the previous target of 20%, and significantly lifts the goal of reforestation to 6bn cubic metres of forest stock from 4.5bn. In the earlier document, there was no figure given for solar and wind capacity by 2030, but the new submission states this will be 1,200GW.

However, the reaction among analysts was that the new climate plan is disappointingly short of fresh details. The main targets of the updated NDC were announced last year by China’s president, Xi Jinping, and are insufficient to keep the world on course to hold global heating to no more than 1.5C.

Belinda Schape, from the E3G thinktank, said the recent warning by the world’s leading climate scientists required nations to step up further than they were willing to do last year.

“Things have changed since a year ago. The recent ‘code red warning’ by the IPCC puts China’s targets into a different light and increased ambition from China is crucial to keeping global warming below dangerous levels.

“China could still bring large contributions to the table at G20 and Cop26 by supporting a political commitment to keep 1.5C within reach and clarifying the role of coal in its power system.”

Hopes that a Chinese NDC might be a major mood-booster in the run-up to the Glasgow summit were always likely to be misplaced.

President Xi had already recently pledged to stop building coal-fired power plants abroad, which was an important and progressive step, but climate campaigners say it is now time for the country to take more actions domestically to rein in greenhouse gas emissions this decade.

Li Shuo of Greenpeace said: “China’s decision on its NDC casts a shadow on the global climate effort. In light of the domestic economic uncertainties, the country appears hesitant to embrace stronger near-term targets, and missed an opportunity to demonstrate ambition.

“The planet cannot afford this being the last word. Beijing needs to come up with stronger implementation plans to ensure an emission peak before 2025.”

However, others said it was significant that China had put those verbal commitments in writing.

The new NDC is also far less than many analysts say China could easily manage. With its huge investments in renewable energy in recent years, the country has already made substantial changes to its high-carbon economy, and the plunging price of low-carbon technology should make the transition even easier, leading many analysts to conclude that China could, with not much extra effort, cause its emissions to peak in about 2025.

China will again be the focus of sustained diplomatic efforts by some of the other major players at the talks, including the US and the EU, when the leaders of the G20 meet in Rome this weekend ahead of Cop26 – though without Xi, who will be represented by high-ranking officials.

These countries believe that although the headline emissions cuts are unlikely to be improved, there could be room for movement by China in key issues such as the eventual phase-out of coal.

The mood of those talks will also be highly significant. “The key will be whether China engages constructively,” said one well-placed insider. “The mood has not been depressed by China’s NDC, but there had been hope of [China showing] more leadership, particularly from small developing countries who look to China for that.”

Helen Mountford, the vice-president for climate and economics at the World Resources Institute, said China needed to strengthen its new near-term targets and measures to get on a pathway to reach its 2060 carbon neutrality goal, and that this was within its reach.

“Our analysis shows that China can step up its efforts to reducing emissions while also enjoying economic growth and a more sustainable environment,” she said.

Senior sources at the talks have previously said “China likes to underpromise and overdeliver”, but the conservative estimate of future emission reduction efforts will not cheer diplomats hoping for a breakthrough from the world’s biggest emitter.

The UK hosts and the other big nations who want a deal at the Glasgow summit will now be left with the problem of how to bridge the substantial gap between the likely emissions reductions arising from all the NDCs so far and the 45% cuts scientists say are needed in emissions by 2030, compared with 2010 levels, to hold heating within the 1.5C limit.

One way, mooted by the UN secretary general earlier this week, is to force countries back to the negotiating table every year to reconsider their pledges, which would be unpopular with many.

China could also soften its stance by making commitments on reducing its reliance on coal, increasing its low-carbon investments overseas or enhancing other plans such as fostering carbon sinks. Bernice Lee, the research director for futures at the Chatham House thinktank, said: “We cannot sugarcoat it. It is disappointing and off the mark and not befitting of the world’s largest emitter. It is symptomatic of a broader trend/shortfall where major economies are not making the kind of cuts needed to get 1.5C within reach just yet.

“China has lowballed its target and missed a chance to be recognised as a global leader. The plan says emissions will peak before 2030 – for all our sakes we need that date to be far sooner.”