UNEP says a 1.5C overshoot is now unavoidable and peaks look like 1.8C at best

The United Nations Environment Programme said on 2 September that global temperature will pass 1.5C above pre-industrial levels “within a few years” and that the exceedance is “unavoidable.” The best case in the new assessment peaks near 1.8C this century. Under policies already in force, the median projection is about 2.6C by 2100.

UNEP executive director Inger Andersen, briefing on 1 September, put the political line in one sentence: “Obviously, yes, we have climate procrastinated.” Long-term warming is now cited at about 1.4C, with individual years already spiking above 1.5C. 2024 was the first calendar year in which every month sat over the Paris mark. The UN had still treated that as a spike, not a breach, until a multi-year average crossed the line. That distinction is now being retired.

What the report asks governments to do instead

The paper shifts the official task from “keep 1.5 alive” to “limit the overshoot.” Bringing the thermometer back below 1.5C is described as possible but highly uncertain. It would take steep cuts in current emissions plus carbon dioxide removal, including new forests and engineered capture. UNEP said removal is “critical” and also said it is not a substitute for cutting the flow.

The overshoot is expected to last several decades. In the most favourable path, temperatures could ease toward 1.6C by 2100 after a 1.8C peak. Every extra year above 1.5C, the authors write, raises the chance of losses that do not reverse when the number later falls: ice sheets, permafrost, coral reefs, glaciers.

That is the change in official language. Glasgow in 2021 ran on the slogan “keep 1.5C alive.” Last year’s conference in Brazil closed with a line about keeping 1.5 “in reach.” Simon Stiell, the UN climate lead, used similar wording there. The new UNEP text tells the same system that the target year has moved from prevention to damage control.

What “unavoidable” does and does not mean

It does not mean every national pledge is worthless. The 1.8C peak is the path if those pledges are actually built. The 2.6C figure is the path if they are not. The gap between the two numbers is the remaining policy lever. It does mean that the legal and diplomatic architecture built around a 1.5C ceiling now has to explain an overshoot that the secretariat itself calls certain.

Climate-vulnerable states had already treated 1.5C as a survival line, not a preference. The UNEP admission lands as confirmation of a forecast they have been making in negotiations for years. The operational question for the next conference is narrower: how long the overshoot lasts, and whether carbon removal is treated as a budget line or as a slogan.

Andersen’s phrase will be quoted. The numbers that will be used in finance ministries are 1.8 and 2.6. One is the ceiling if promises are kept. The other is the path if they are only filed.