Attempts to stoke a climate crisis culture war must be rejected or the world will face economic disaster, the UN’s climate chief has warned.

Simon Stiell, the executive secretary of the UN Framework Convention on Climate Change, warned that this year’s “hot as hell” summer had killed tens of thousands of people in Europe alone and “hammered” infrastructure, businesses and economics, costing a likely €180bn (£155bn), as well as leading to forced migration around the world.

“The climate crisis is now a continent-wide economic security emergency,” he told a committee of the European parliament on Thursday morning. “We’ve seen mass evacuations. Power stations closed. And trade routes choked. Crops lost. Yields down. And food prices up – and set to rise further.”

He said political polarisation over climate action was not in the interests of voters and would lead to far worse outcomes. “Climate is sometimes seen as a partisan issue, as territory in the culture wars,” he said. “That is palpably false … Climate cuts across the core concerns of voters, whatever their politics: [affecting] family health, community safety and economic stability; affordable food and available water; jobs, business costs and household bills.”

With populist parties in the EU and around the world calling for backtracking on policies to cut greenhouse gas emissions, Stiell hit out at some of those politicians’ key talking points, including on migration, which he said was increasing as a result of extreme weather. “To be soft on climate action is to be soft on inflation, and the cost of living, soft on sovereignty and security, and soft on economic growth and jobs. The fossil fuel crisis is also pushing up the costs of government borrowing, meaning less fiscal space to deliver vital services that populations need and expect.”

Simon Stiell: ‘If humanity doesn’t cut the fossil fuel pollution … this summer’s brutal heat, fires and droughts will seem mild compared to the permanent climate nightmare that will follow.’ Photograph: Rajat Gupta/EPA

Stiell’s warnings came as the EU’s climate monitoring service released data showing August 2026 was the joint hottest month ever recorded around the world. Global temperatures reached 1.65C above preindustrial levels, scientists said on Thursday, amid warnings of further heating.

Last month tied with July 2023 for the hottest on record, according to the EU’s Copernicus Climate Change Service. Sea surface temperatures also soared to their highest levels on record for August.

These temperatures were recorded before the coming El Niño weather system had made much of an impact. El Niño is a naturally recurrent phenomenon whereby wind changes over the Pacific lead to rising ocean temperatures and the transfer of huge amounts of heat to the atmosphere, with the consequences felt around the world in floods, droughts and heatwaves.

This year’s system, likely to reach its full strength towards the end of the year, is forecast to be potentially the most intense on record, as it is now supercharged by the climate crisis.

A wildfire rages near Santa Maria, California. Photograph: Benjamin Hanson/Middle East Images/AFP/Getty Images

Friederike Otto, a professor of climate science at Imperial College London, said: “While El Niño is starting to ramp up the heat, the underlying driver [behind this year’s high temperatures] remains our relentless burning of fossil fuels. Climate change makes every El Niño hotter, and until we stop burning coal, oil and gas, these record-shattering months will simply keep on coming.”

The effects of August’s extreme heat are still being felt around the world, in the aftermath of devastating wildfires, damage to harvests, excess deaths from heatwaves and disruptions to transport, business and public services in many countries. Food price inflation is likely to increase further, as the impacts of smaller harvests are felt in domestic markets and imports.

Stiell said: “If humanity doesn’t cut the fossil fuel pollution … this summer’s brutal heat, fires and droughts will seem mild compared to the permanent climate nightmare that will follow.”

Heatwaves in the UK left green spaces parched. Photograph: Thomas Krych/Zuma/Alamy

Although temperatures exceeded 1.5C above preindustrial levels, set in the 2015 Paris climate agreement as the lower of two limits that governments would strive to keep, such highs would need to continue for several years before the agreement was judged to be breached.

Data from the Copernicus Earth observation satellite service confirmed that western and central Europe, as well as areas of Scandinavia and south-eastern Europe, had experienced much drier than usual conditions over the summer, while around the world much of the south of the US, northern Mexico, parts of Canada, the Maghreb, part of the Horn of Africa, Siberia, large parts of central Asia, China, South America, South Africa, and northern Australia were all also drier than average.

The Romanian section of the Danube had exceptionally low water levels because of extreme heat. Photograph: Vadim Ghirdă/AP

The more temperatures rise above the 1.5C threshold, the greater the chance of reaching planetary “tipping points” that could push temperatures much higher and irretrievably break down key stabilisers of the climate system, such as the Arctic ice cap and the Amazon rainforest. Ruth Fuller, chief adviser on climate to the environmental charity WWF UK, said: “This year has seen records broken left, right and centre, increasing the risk that natural systems will irreversibly change once they are pushed past tipping points.”

Samantha Burgess, the strategic lead for climate at the European Centre for Medium-Range Weather Forecasts, which operates the Copernicus service, said: “August 2026 was a remarkable month in the global climate record. It was both the warmest August and the warmest month ever recorded, with global temperatures reaching 1.65C above preindustrial levels, marking the return of global temperatures above 1.5C.

“Combined with record global sea surface temperatures and the warmest summer on record for western Europe, these observations show how climate change is driving extremes across the atmosphere and the oceans. The impacts of these conditions are increasingly being felt by communities, economies and ecosystems across the world.”