The world was for 10 years a temperature that was not to be crossed. So this week the United Nations is effectively giving in that line is going to be crossed regardless, and not in a begrudging manner but more in a triage kind of way. The UN Environment Programme's first-ever assessment of global warming out of Nairobi shows clearly that global temperatures are on course to reach the 1.5°C benchmark agreed in the 2015 Paris accord in the not too distant future, as continued coal, oil and gas burning push climate risks and impacts to dangerous new levels.

Limiting Overshoot is an unusual kind of UN report in that it does not claim that the target is still achievable in its original form. Rather it charts the consequences of crossing the line, and the possibility that the world may eventually pull itself back under it.

Those numbers behind that change are startling. Even in the best scenario, where governments make their boldest commitments, warming will not start to ease until near mid-century when it will reach a maximum of 1.8°C. With the current policy, the path is more dire, with temperatures heading towards 2.6°C above pre-industrial levels at the turn of the next century. This is no rounding error. It's the distinction between a sustainable overshoot and a permanently changed climate system; it's why UN Secretary-General António Guterres in his accompanying message to the report has used strikingly harsh language, warning that the world is likely to reach the 1.5-degree threshold in the next few years.

The plan in the hopper is what scientists call an "overshoot, peak and decline" approach: accept a world that runs hot for a short time, push as hard as possible to keep that short time as short and shallow as possible, and then work hard to reduce the temperature in a steep curve to the original expected target by the end of the century through large-scale carbon removal.

It is not a surrender and UN officials have carefully labelled it as such. However, it's a strategic retreat, and its consequences are real and can be seen on the ground. Homes and belongings were swept away in the district of Nuwakot, in the beginning of September, due to flash floods in Nepal which is still being assessed. Wildfires continued to encroach on to California's Highway 1 in late August near Big Sur. The Danube's water levels have fallen so low that part of the river beds, which are normally covered and have been known for generations are now visible. Another vicious heat wave hit Northern India early this year. None of these events alone is a proof of the overshoot thesis. Together they are the consistency of a world in the throes of the early stages of the report's description.

Countries particularly sensitive to climate change have been more alarmed than accepting of the reaction. Those in Pacific island states reacted with chilling dismay to the projections that the rest of the world can't escape, with analysts at the World Resources Institute putting the issue succinctly: No country is safe in a world that exceeds 1.5°C and the longer we wait the more the costs will hit the countries least able to bear them. For 20 years the main fault line of climate diplomacy has been that of asymmetry: that the rich economies set the emissions trajectory while poorer, lower-emitting nations are stuck with the physical damage. Overshadowing makes it worse but does not cure it.

Under the alarm there is a real economic narrative that is distinct from politics. The total amount of investment in global energy, including in renewables, grids, storage, nuclear and efficiency, is projected to be between 3.2 and 3.4 trillion dollars this year and for the first time, the clean energy portion of that investment, with renewables accounting for just under half of that total, is on the planet to beat the fossil fuel investment share, which is just under two dollars for every one dollar spent on clean energy.

Solar will be attracting the largest amount of capital this year, more than the total global oil supply chain. Much of that transition is being spurred less by climate concern than by energy security fear as governments observe oil and gas producers on the move being threatened by conflict and realise that wind and solar power can't be kept out of a country or switched off by an adversary. A separate UNEP study estimated that switching to more efficient cooling technology could result in a global savings of 43 trillion dollars in avoided electricity and infrastructure costs in the next few decades, a sum that is dwarfed by nearly all spending on adaptation today.

Carbon removal, which was a niche business several years ago, is now also at the centre of the plan for necessity, not necessarily choice. While all versions of the "peak and decline" pathway outlined by UNEP involve the world stopping the emission of carbon into the atmosphere, they all require actual carbon removal at a significant level. Venture investment in the sector has been increased by some 700% over five years and oil majors and utilities are now funding projects to remove hundreds of thousands of tonnes of CO2 each year. Whether the industry can grow sufficiently quickly to make a significant difference, rather than just being a political negotiating tool for other industries to reduce emissions more slowly is the most disputed issue among scientists examining the report.