The summit hosted by the United Kingdom has been described as " the world's last best chance" to prevent global warming from reaching dangerous levels, and is expected to feature a flurry of new commitments from governments and businesses to reduce their emissions of greenhouse gases.

But climate campaigners say behind-the-scenes lobbying before the summit could hamper efforts to achieve an ambitious deal that would ensure the world stands a chance of capping global warming at 1.5C as agreed in Paris in 2015.

"This Glasgow meeting really is a vital moment where governments need to be courageous," said Jennifer Morgan, the executive director of Greenpeace International.

"They need to show they've understood the science, listen to their people and go much further than they've been stating thus far," she told the Associated Press in an interview.

By doing so, governments would "give that kind of hope and confidence to their people that they got this and that they're willing to do things that their corporate interests don't want them to do," she added.

Morgan pointed to leaked documents showing how countries such as Australia, Brazil and Saudi Arabia are apparently trying to water down an upcoming UN science panel report on global warming as evidence of the way in which some governments' public support for climate action is undermined by their efforts behind closed doors.

Documents obtained by Greenpeace indicate how those countries wanted the Intergovernmental Panel on Climate Change to remove references to the need to shut down coal-fired power stations, reduce meat consumption and focus on actual emissions cuts rather than ways to capture carbon dioxide already released into the atmosphere.

A spokesman for the IPCC's secretariat in Geneva downplayed the effect such lobbying efforts have on the panel's final reports.

"Review by governments and experts is a fundamental part of the IPCC process for preparing reports," said the spokesman, Jonathan Lynn.

"The IPCC principles are designed to ensure that this review contributes to a comprehensive, balanced and objective assessment in an open and transparent way."

Greenpeace's Morgan said much of the lobbying is driven by corporations, some of which will also be at the so-called COP26 talks - including as part of government delegations.

"They'll try and use this COP to show that they care, that they are really doing a lot," said Morgan.

"There'll be a big greenwashing effort in Glasgow that needs to be called out and recognised."

Governments, too, are likely to use the UN talks to announce new climate measures, even as they lobby against others, she said.

"If you look at what they're doing to try and hold back the world from moving forward, it's stunning," she said.

"It's immoral, it's unacceptable."

Greenpeace and other environmental campaign groups have been critical of a wave of announcements by countries and industry groups, ranging from airlines to shipping firms, to aim for "net zero" emissions.

Rather than cut greenhouse gas emissions to nil, those aiming for net zero pledge to release only as much carbon dioxide or other gases into the atmosphere by a certain date as can be captured again.

The math around net zero is murky and activists say if it is not scientifically rigorous that target risks detracting from the effort to cut emissions as quickly as possible.

"(Some companies) want to continue what they're doing, but they want to pay just to plant trees somewhere else," said Morgan.

"That is not the solution to the nature and biodiversity crisis."

Australian Associated Press