Global temperature rise: the UN says we will cross 1.5°C within a few years – and must return from above

Global temperature rise will cross the 1.5°C threshold within the next few years. That is not a forecast but the opening finding of Limiting Overshoot, the report published by the United Nations Environment Programme (UNEP) in September 2026. The document is not, however, about giving up: it examines how to keep the overshoot as small and as short as possible, and then return below 1.5°C by the end of the century. It is the work of dozens of researchers, and it states plainly what climate policy communication has largely been circling around.

What exactly does the UN report say?

The logic is simple; the consequences are not. The long-term goal of the Paris Agreement remains 1.5°C — the International Court of Justice in its 2025 advisory opinion described this as the parties’ primary temperature goal, and a UN General Assembly resolution reinforced it. Emissions cuts, however, have not been fast enough to avoid crossing the line.

From here the goal does not disappear; the direction reverses. 1.5°C must now be approached from above. First slow the warming, then peak it, then bring it down. The report calls this an “overshoot, peak and decline” pathway. It is not a desirable scenario — the report itself describes it as simply the best remaining option.

Where we stand: 1.4°C and a three-year carbon budget

A few numbers form the backbone of the report:

• Human-induced warming currently sits at around 1.4°C above pre-industrial levels and is rising at roughly 0.25°C per decade.
• Extrapolating the trend, global temperature rise could reach 1.5°C around the end of this decade. A World Meteorological Organization forecast puts a three-in-four chance that the 2026–2030 five-year mean already exceeds that level.
• 2024 was the first calendar year with a global mean above 1.5°C. A 2025 study concludes the world has now entered a 20-year period whose mean warming is 1.5°C.
• The remaining carbon budget — the CO₂ that can still be emitted — is just 130 billion tonnes from 2026 onwards for a 50 per cent chance of holding 1.5°C. Fossil fuels and industry alone produced around 40 billion tonnes of CO₂ in 2024. At that rate the budget is exhausted in roughly three years.
• Every five years of high emissions adds about 0.1°C to peak warming. The more than 400 billion tonnes of CO₂ emitted since 2015 have already raised the lowest achievable warming by about 0.2°C.
• If every country delivers its pledges plus its net-zero targets, expected peak warming is around 1.8°C. The most ambitious pathways that incorporate observed emissions up to 2025 project a peak of 1.6–1.8°C at 50 per cent probability.

That last point is the crux of the argument. Delay is not merely more expensive; it closes off options. Whatever is not cut today would have to be pulled back out of the atmosphere later through carbon dioxide removal — and that capacity is narrow.

Why there is no “safe” world above 1.5°C

One of the report’s central messages is that exceeding 1.5°C should not be read as safe or acceptable. Above that level there are no benign scenarios. What the document lists:

What is already happening. Between 2023 and 2025 more than 80 per cent of tropical coral reefs experienced bleaching, with mass bleaching documented in at least 83 countries and territories. In February 2025 combined Arctic and Antarctic sea ice hit an all-time low, and the oldest, thickest multi-year ice has shrunk by more than 95 per cent since the 1980s. Of all glacier loss since the 1970s, more than 40 per cent occurred in the last decade (2015–2024), with 6 per cent lost in 2023 alone.

Heat and human life. Over the past two decades more than 50 unprecedented, high-impact heatwave events have been documented. Between May 2024 and May 2025 roughly half the world’s population experienced at least 30 days of extreme heat. During the European summer heatwave of 2025, heat-related deaths were estimated to have tripled, with the increase attributed to global warming.

Food and water. Without effective adaptation, global food production could fall by up to 14 per cent by 2050. Glaciers could lose more than a quarter of their mass by 2100, contributing 9–12.5 cm of sea-level rise and permanently altering water availability in many regions.

Irreversible tipping points. Risks grow for systemic shifts in the West Antarctic and Greenland ice sheets, the Atlantic Meridional Overturning Circulation (AMOC) and the Amazon rainforest. Warm-water corals have a warming threshold of 1.2°C — meaning it has already been passed. Ocean acidification has cut coral regrowth and calcification rates by 20–40 per cent.

The hardest finding: even if a return below 1.5°C is secured, many losses will be permanent. Sea-level rise, species extinctions and ecosystem regime shifts continue well past the temperature peak.

Reversing global temperature rise: what carbon dioxide removal can and cannot do

This is perhaps the most sobering chapter. Carbon dioxide removal (CDR) comes in two forms: conventional — afforestation, ecosystem restoration — and novel, such as bioenergy with carbon capture and storage (BECCS), direct air carbon capture and storage (DACCS), biochar and enhanced rock weathering.

The numbers are not flattering:

• Novel CDR currently accounts for less than 0.1 per cent of conventional removal.
• At today’s scale of afforestation and forest management, and with zero residual CO₂ emissions, it would take more than 100 years to claw back 0.1°C.
• Geological storage is finite too. If residual emissions stay around 10 billion tonnes a year from 2050, estimated sedimentary-basin capacity could be exhausted by 2200 just to maintain net-zero.
• Overall: even under optimistic scaling, CDR is unlikely to deliver more than a few tenths of a degree of reversal this century.

Only one conclusion follows. CDR is needed in addition to emissions cuts, not instead of them. And it can contribute credibly to a return below 1.5°C only if peak warming stays well below 2°C. Beyond roughly 1.8°C, a decline to 1.5°C within this century becomes increasingly difficult.

Three phases, one schedule

The report divides the global response into three interlocking phases:

1. Immediate response — as temperatures approach and then exceed 1.5°C: slow warming quickly through deep emissions cuts, especially of methane and other short-lived climate pollutants, alongside urgent adaptation protecting the most vulnerable people and ecosystems.
2. Coping and containment — as temperatures peak: deep, sustained decarbonization to at least net zero, plus societal resilience while managing severe impacts.
3. Long-term resilience — as temperatures decline and stabilize: sustained net-negative CO₂ emissions, and lasting adaptation where irreversible limits have been reached.

In practice these phases will coexist across regions. And the report insists that mitigation and adaptation cannot be separated. Many interventions serve both — expanding urban tree canopy, for instance, reduces heat-related illness and death while cutting the need for energy-intensive cooling.

Where waste management enters the picture

This is the part that speaks most directly to the waste sector. Methane is responsible for around 0.5°C of current global warming, and cutting it early can significantly lower peak warming while delivering immediate air quality and health benefits.

Among the low-cost methane abatement options the report names the oil and gas sector — but alongside it, specifically:

• reducing food loss and waste,
• waste segregation,
• methane capture from landfills.

High-leverage measures could deliver up to 41 billion tonnes of CO₂-equivalent in annual reductions by 2035 at under USD 200/tCO₂e, with about half of that potential below USD 20/tCO₂e.

There is a further, more striking finding: agriculture and waste are the next frontier for methane mitigation. Most fossil-derived methane can largely be eliminated by 2050 at relatively low cost under stringent policy. What remains after that comes mainly from agriculture and waste — terrain that is harder technically, culturally and socially, and that has received disproportionately little targeted mitigation policy. The report classes it explicitly as hard-to-abate.

Translated into practice: separate collection, diverting organic waste from landfill, landfill gas recovery and cutting food waste are not “soft” environmental topics but measurable levers on peak temperature. The kind of work this site has covered for 13 years now appears in a UN report as part of a global temperature budget.

Equity: responsibility and exposure are not evenly shared

A recurring theme is that countries with greater historical responsibility and greater capability should act hardest and fastest. Countries disproportionately affected — particularly small island developing states, some of which face partial or complete submersion — must be genuine participants in global decision-making.

The document also argues that the legacy consequences of overshoot raise questions of justice, power and political legitimacy that reach beyond what current climate governance can handle. When a community has to relocate, or an agricultural system is reconfigured for higher temperatures and then has to be reconfigured again, these are institutional and intergenerational problems, not technical ones.

What to take away

The report is not a prescription but, in its own words, a foundation for sustained research, learning and decision-making. Its practical message is sharp:

• Crossing 1.5°C is settled. How high the peak goes and how long the overshoot lasts is not. Both depend on what happens this decade.
• Every tenth of a degree and every year counts. Five years of delay adds 0.1°C to the peak, and every tenth avoided spares lives, ecosystems and economic loss.
• Waiting for a technological rescue is not a strategy. Carbon removal is necessary but can claw back at most a few tenths of a degree this century. The bulk of the work sits on the emissions side.
• Methane is the fastest lever. And a large share of it is a waste management and food systems question — meaning there is work to do at municipal, utility, business and household level.

Inger Andersen, UNEP Executive Director, closes her foreword by noting that this is not the future we sought, and that a return to 1.5°C is not assured. But limiting the magnitude, duration and consequences of overshoot, while keeping the possibility of return alive, is the best remaining option.

Frequently Asked Questions About Global Temperature Rise

When will global temperature rise cross 1.5°C?

Within the next few years, according to the UNEP report. Human-induced warming currently stands at around 1.4°C and is rising at roughly 0.25°C per decade, so on trend it could reach 1.5°C by the end of this decade. The World Meteorological Organization puts a three-in-four chance that the 2026–2030 five-year mean already exceeds that level.

What does an overshoot, peak and decline pathway mean?

It means the 1.5°C goal must now be approached from above. Temperature first crosses the threshold, then peaks, then falls back below 1.5°C by the end of the century. The report calls this not a desirable scenario but the best remaining option. How high the peak goes and how long the overshoot lasts is decided this decade.

How much of the global carbon budget is left?

Only about 130 billion tonnes of CO₂ from 2026 onwards for a 50 per cent chance of holding 1.5°C. Fossil fuels and industry alone emitted 40 billion tonnes in 2024, so at that rate the budget is exhausted in roughly three years. The report notes that every five years of high emissions adds 0.1°C to peak warming.

Can carbon dioxide removal solve the problem?

Not on its own. Novel carbon dioxide removal currently accounts for less than 0.1 per cent of conventional removal, and at today’s scale of afforestation it would take over 100 years to claw back 0.1°C. Even under optimistic scaling, only a few tenths of a degree can be reversed this century. CDR is needed in addition to emissions cuts, not instead of them.

What role does waste management play in climate targets?

Methane is responsible for around 0.5°C of current warming, and the report names cutting food waste, waste segregation and landfill methane capture among the most cost-effective abatement options. It also identifies agriculture and waste as the next frontier for methane mitigation after 2050, once most fossil-derived methane has been eliminated.

Is the damage reversible if we return below 1.5°C?

Only partly. The report states that even with a successful return, many losses will be permanent: sea-level rise, species extinctions and ecosystem regime shifts continue well past the temperature peak. Many communities will have relocated or changed livelihoods by then, and some adaptation limits will have been crossed irreversibly.

Source: United Nations Environment Programme (2026). Limiting Overshoot: Navigating exceedance of 1.5°C and pathways towards return. Nairobi. ISBN 978-92-807-4301-2. DOI: https://doi.org/10.59117/20.500.11822/49857 · Report available at: https://www.unep.org/resources/limiting-overshoot-navigating-exceedance