Catastrophic global warming can be avoided with a deal at a crunch UN climate change summit in Paris this December because “ultimately nothing can compete with renewables”, according to one of the world’s most influential climate scientists.

Most countries have already made voluntary pledges to roll out clean energy and cut carbon emissions, and Prof John Schellnhuber said the best hope of making nations keep their promises was moral pressure.

Schellnhuber is a key member of the German delegation attending the Paris summit and has advised Angela Merkel and Pope Francis on climate change.

He said there was reason for optimism about the Paris talks, where at least 80 heads of state are expected. “That is a very telling thing - a sign of hope - because people at the top level do not want to be tainted by failure,” he said.

If a critical mass of big countries implement their pledges, he said in an interview with the Guardian, the move towards a global low-carbon economy would gain unstoppable momentum.

“If some countries really honour their pledges, including China, Brazil, South Africa, US and Europe, I think we will get a dynamic that will transform the development of the century. This is not sheer optimism – it is based on analysis of how incumbent systems implode.”

In July, Schellnhuber told a science conference in Paris that the world needed “an induced implosion of the carbon economy over the next 20-30 years. Otherwise we have no chance of avoiding dangerous, perhaps disastrous, climate change.”

“The avalanche will start because ultimately nothing can compete with renewables,” he told the Guardian. “If you invest at [large] scale, inevitably we will end up with much cheaper, much more reliable, much safer technologies in the energy system: wind, solar, biomass, tidal, hydropower. It is really a no-brainer, if you take away all the ideological debris and lobbying.”

India, for example, aims to deliver 350GW of renewable energy in the next 10 years, the equivalent to 300 nuclear power stations, he said. “That is mind boggling and would be the final nail in the coffin of coal-fired power stations,” Schellnhuber said. “If India delivers on that pledge, it will be a tipping point for that country.”

He said the approach taken for the Paris talks, asking each nation to put forward a pledge, had resulted in half the emissions cuts needed to avoid more than 2C in warming, the level widely considered as dangerous. “These are pledges only, but nevertheless this bottom-up approach is driving change, and that is amazing as it is the weakest approach,” Schellnhuber said.

The key, he said, was that these pledges are honoured and future reviews deliver the rest of the cuts needed. But he warned there will be no international force to check and enforce carbon cuts, as nations would not allow such a challenge to their sovereignty.

“The verification will not be delivered by an international scheme,” he said. “You will not send in emissions inspectors like people wanted to send to Iran [for nuclear technology inspections].” Instead, he said: “It is prestige, it is image, it is a moral issue, it is how you appear to the world. If the Chinese, for example, make a pledge, they want to keep it. They do not want to lose face.”

Public pressure is “really holding the key to this”, said Schellnhuber, who has attended most of the 20 previous UN climate summits. “The last, best hope we have is moral argument.” He said that Germany’s aim to cut carbon emissions by 40% by 2020 was a tall order, because dealing with its lignite coal-fired power stations will be “very expensive and difficult”. But he said: “Merkel will do everything to achieve this or it will be seen as a national failure.”

The biggest danger for the Paris summit, he said, was the $100bn a year from 2020 promised by rich nations help poorer countries cope with climate change, which has yet to be delivered. He said the sum was “peanuts” in the context of global investment flows, but that a failure to deliver would “make countries in the global south very angry”.

“We can afford $100bn across the world, but it seems the OECD [Organisation for Economic Co-operation and Development] countries are still very reluctant,” Schellnhuber said. “It will divert attention from the serious work – making sure the pledges are honoured.”