Cuts in climate pollution so far promised by countries around the world will fail to prevent floods, droughts, heatwaves and other catastrophic changes, according to the latest analysis by the United Nations.

Current commitments to reduce carbon emissions in the run-up to a crucial international climate summit at the end of the month are only about half of what’s needed to reduce the risk of disaster, creating a widening “emissions gap” over the next 15 years, the UN has warned.

Environmentalists, experts and politicians fear that the Paris summit of world leaders – the most important since Copenhagen in 2009 – could end in failure unless major polluters agree further  reductions. Some insist they are still optimistic about the outcome, but others are distinctly pessimistic.

The world is aiming to limit global warming to an average of less than two degrees centigrade above pre-industrial temperatures. Scientists say this is the limit beyond which the impact of climate change is likely to become catastrophic and irreversible – although some also suggest that a rise of 1.5 degrees could have serious consequences.

“Paris is obviously going to be a failure,” said Dr Richard Dixon, director of Friends of the Earth Scotland.

“The proposed targets fall far short of the effort needed to deliver the 2ºC that world leaders have promised, let alone the 1.5ºC temperature limit which is needed to protect the most vulnerable people, nations and wildlife.”

Most countries have now set out in reports to the UN for the Paris summit the cuts in emissions they plan to achieve. An analysis by the UN Environment Programme has added them all together and concluded that they will only result in a reduction of around 11 gigatonnes of carbon by 2030 – less than half of that required to give the world a good chance of staying within the two degree limit.

Dixon pointed out there was also huge disagreement on the funding that poorer countries needed from richer countries to help cope with the ravages of climate change. “However, it is still important to put pressure on to get the best deal out of Paris,” he argued.

“We’ll be in the negotiations and on the streets of Paris and our messages will be about opposing fossil fuels, starting with fracking, promoting community renewables, and shifting public and private investments from dirty energy to clean energy.”

Campaigners are planning a big march through Edinburgh on November 28 demanding more action to cut climate pollution. Protests are also planned in 70 other cities around the globe.

The Scottish Government has won international praise for its “world-leading” aims of reducing emissions 42 per cent by 2020, and 80 per cent by 2050. But it has failed to meet the annual targets needed to achieve those aims in each of the last four years.

Scottish Climate Change Minister Dr Aileen McLeod is planning to join the Edinburgh protest and take part in the Paris summit. First Minister Nicola Sturgeon is also considering going to Paris, along with UK Prime Minister David Cameron and US President Barack Obama.

Lang Banks, the director of WWF Scotland – who will also be in Paris – paid tribute to recent moves by the US and China towards greater emissions cuts. This meant there were “positive prospects for meaningful progress”, he argued.

“But we should not kid ourselves. What is currently on the table in the way of a draft text and individual country pledges are not yet enough to keep people and nature out of danger,” he warned.

“The leadership shown by countries like Scotland with our ambitious climate change targets is very helpful, but would be far more powerful if we could show we were meeting those targets and our society was on track to become a low-carbon powerhouse.”

According to the Scottish Greens’ Europe spokesman, Ross Greer, the Scottish Government had “a job to do to rebuild its credibility”. He called on ministers to use the forthcoming budget to help low carbon housing, transport and land use.

McLeod, however, insisted Scotland had “a very strong story” to tell in Paris. “We should be proud Scotland cut its greenhouse emissions by a massive 38 per cent between 1990 and 2013 – much more than the 31 per cent originally envisaged,” she said.

She has written to the UK Energy Secretary Amber Rudd urging her to reverse UK cuts in renewable subsidies, which had made a crucial contribution to reducing climate emissions. McLeod warned that Westminster could be fined if it fails to meet legally-binding targets to increase renewable energy.

The world had to make further cuts in climate pollution for the sake for future generations, McLeod argued. “The international community will have to match Scotland’s commitment if the Paris climate summit is to form the foundation for a truly effective global response on climate change in the years ahead.”

Aberdeen professor Anne Glover, former chief scientific adviser to the Scottish Government and to the European Commission, wanted to be positive. “We have to be optimistic for  Paris,” she told the Sunday Herald.

“If we think it will fail, it’s like giving it permission to fail and also an acknowledgement that our world leaders aren’t leaders at all,” she contintued.

“Scotland invented the modern world through science, engineering, technology and philosophy and could also help protect our future on the planet.”

According to a working document from the French government, which will be leading the Paris talks, there are still 30 core issues that remain unresolved. The latest draft text for the final declaration runs to 55 pages and still has 1,490 brackets around areas of disagreement.

The Paris summit, which runs from November 30 to December 11 and is known as COP21, is the latest stage in an extraordinary decades-long effort of international diplomacy to try and combat climate change. Leaders are still hoping that something substantial can be agreed.

After a preparatory meeting of ministers from 60 countries in Paris last week, the French foreign minister Laurent Fabius sounded optimistic. “An ambitious compromise is in sight and a series of concrete proposals have been made in that light,” he said.

The anti-poverty group, Oxfam, argued that Paris must make a step forward for the sake of the world’s poor, who were the hardest hit but the least responsible. “Climate change is already forcing poor people into a life of hunger and having a devastating effect on their lives,” said the head of Oxfam Scotland, Jamie Livingstone.