The United Nations was presented with a roadmap to avoid a climate catastrophe on Tuesday, prescribing specific actions for the world’s biggest economies to keep warming below 2C.

In a report prepared for the secretary general, Ban Ki-moon, experts from 30 international institutions set out a range of strategies for the economies responsible for more than two-thirds of global emissions.

The initiative is the first of its kind to try to make concrete plans around the various targets that have been discussed at the UN climate change negotiations over the last two decades, said Jeffrey Sachs, director of Columbia University’s Earth Institute, and a leader of the Pathways to Deep Decarbonisation Project.

“All we have been doing in these negotiations for all these years is talking about things in the abstract. It’s not producing the deep technological changes that can get us to a low-carbon global economy,” he told the Guardian.

The report, with its detailed data on electricity supply, transport and shipping, and building codes in each country, was aimed at remedying this by making the targets operational, he said.

It is hoped the study will help to build momentum for a UN climate change summit in New York this September, and so advance the negotiations to reach a global climate deal by the end of 2015.

The study looks at the world’s 15 biggest economies: America, Australia, Brazil, Britain, Canada, China, France, Germany, India, Indonesia, Japan, Mexico, Russia, South Africa, and South Korea, which between them account for 70% of global emissions.

It rejects the idea that has taken hold since the failed Copenhagen climate summit in 2009 that warming of 4 or 5C is already inevitable.

“We do not subscribe to the view held by some that the 2C limit is impossible to achieve and that it should be weakened or dropped altogether,” the report said, adding that the science about the 2C threshold was clear.

“The political risks of jettisoning the 2C limit are also significant,” the report went on, and would further weakening the chances of any action.

Instead, it was time for leaders to direct government officials and independent institutions to work on the technologies that would actually produce reductions in emissions.

To date, the targets discussed at the UN climate talks were detached from reality, the report said.

“By and large national targets are not derived from an assessment of what will be needed to stay within the 2C limit,” it said.

Sachs said that was in part a function of the UN negotiations process, that left a highly technical discussion to diplomats.

“It put the lawyers out front and left the technologists out of the room, and the result is that we have had 21 years of lawyering and no success in application of the international framework,” he said.

The result, he said, were emissions reductions targets that were far too conservative to avoid 2C warming. “I didn’t hear President Obama say we have a 2C agreed global warming limit, and I am basing American policy on making sure that is successful. I have not heard any leader saying that,” he said. “Actually, now we have a report that will tell them what it would take.”

Those options vary widely according to the country. The report envisages that Britain by mid-century would generate about 35% of its electricity from nuclear power plants and 40% from coal using carbon capture technologies.

America too will remain heavily invested in coal, and could generate up to 35% of its electricity from coal using carbon capture technologies.

South Africa, which is now heavily dependent on coal, could generate 80% of its electricity from solar energy, while countries such as Australia could achieve cuts in their emissions by switching to electric cars and public transport.

The report acknowledges that the technologies it incorporates in its findings – including carbon capture – are not yet available on a widespread, commercial scale.

It also makes no attempt to offer a cost-benefit analysis of the sweeping transformation that would be needed in all 15 countries to keep warming within 2C.

Sachs said those aspects would be dealt with in a final report due next year.