The fourth survey of nearly 70 experts found a sharp drop in confidence from last year, when nearly half of respondents thought carbon dioxide emissions had already peaked or would do so in 2025.

Instead, while most said China would peak emissions by its 2030 target, 71 percent now believe that will happen between 2026 and 2030, with most expecting it in 2028.

The shift comes after China issued its first numerical emissions reductions targets this year, pledging to cut greenhouse gases by 7-10 percent within a decade.

But it failed to set a baseline year from which to make those cuts, fueling uncertainty about when its emissions might peak.

As the world's biggest emitter of planet-warming greenhouse gases, China's climate ambitions are closely watched, and there had been hope it might already have reached a peak in carbon dioxide emissions.

Nearly 20 percent of respondents still believe that peak has been reached, but for most "expectations for the exact timing of peak emissions have shifted to slightly later", the research found.

The survey by the Centre for Research on Energy and Clear Air and the International Society for Energy Transition Studies has been carried out for four years.

A peak in China's emissions would mean the amount of greenhouse gases produced by the world's biggest emitter is no long increasing.

But whether and how quickly the figure declines will also be key.

China this week submitted its official climate roadmap with new 2035 goals, including emissions cuts.

Most analysts view the 7-10 percent pledge as unambitious, with more than half surveyed saying they expect the goal to be met and slightly exceeded.

The survey comes shortly before the annual COP climate talks open in Brazil, with several major emitters yet to submit their 2035 roadmaps.