Earth is set to cross 1.5°C — does the climate clock stop there? The UN has a plan for what happens if temperatures overshoot the crucial threshold

For years, limiting global warming to 1.5°C was treated as one of the most important goals in the fight against climate change. A new United Nations assessment now says the world is unlikely to avoid crossing that threshold.

The finding does not mean the climate battle is over. Instead, it marks a difficult shift in strategy.

The United Nations Environment Programme (UNEP), in its new Limiting Overshoot report, says the focus must increasingly turn to how far temperatures rise above 1.5°C, how long that overshoot lasts and whether warming can eventually be reversed.


That means the next phase of climate action will not simply be about preventing 1.5°C warming. It will be about limiting the damage after the threshold is crossed and bringing global temperatures down as quickly as possible.

Earth is already close to the 1.5°C threshold

The 1.5°C figure refers to the increase in Earth's long-term average temperature compared with the pre-industrial period.

Global temperatures have already moved close to that level. Annual averages have temporarily exceeded 1.5°C in recent years, although the Paris Agreement target is assessed using a longer-term warming average rather than a single hot year.

According to UNEP, that longer-term threshold is now expected to be crossed within the next few years.

The distinction matters because a single year above 1.5°C does not mean the Paris temperature goal has technically been breached. The concern is that the underlying warming trend is continuing upward.

What happens when the world goes above 1.5°C?

Crossing 1.5°C would not produce a sudden moment when Earth's climate dramatically changes overnight.

Instead, risks would generally increase as global temperatures rise.

A warmer planet means a greater likelihood of intense heatwaves, heavier rainfall, flooding, wildfires and other climate-related extremes. Communities already exposed to extreme weather are likely to face greater pressure as temperatures climb.

The effects would also extend beyond weather events.

Rising temperatures can accelerate glacier loss, place additional stress on freshwater supplies and threaten ecosystems that are already struggling with environmental change.

For farmers, changing temperatures and rainfall patterns can make food production more difficult, while coastal regions face increasing risks from rising seas.

Every fraction of a degree will matter

One of the central messages of the UNEP assessment is that passing 1.5°C should not be interpreted as a reason to give up on climate action.

The difference between 1.6°C, 1.8°C and 2°C of warming matters.

The higher temperatures climb, the more severe many climate risks become. Limiting the peak could therefore prevent some of the additional damage that would occur under a higher-warming scenario.

UNEP describes the emerging challenge as an “overshoot, peak and decline” pathway.

Under this approach, the goal would be to keep the period above 1.5°C as short as possible before reducing global temperatures.

The best-case scenario still means a warmer planet

Even if countries deliver on their existing climate pledges and longer-term commitments, the outlook remains difficult.

UNEP's most optimistic scenario puts the eventual warming peak at around 1.8°C before temperatures begin to decline.

That would still represent a substantial departure from the 1.5°C goal, but it would be considerably less damaging than allowing warming to continue unchecked.

The situation looks much worse under policies that remain largely unchanged.

On the current policy trajectory, global warming could reach a median estimate of about 2.6°C by 2100, according to the assessment.

The gap between those scenarios highlights why stronger emissions reductions could have enormous consequences for the climate later this century.

Some climate damage cannot simply be reversed

One of the most troubling aspects of temperature overshoot is that lowering global temperatures later would not necessarily restore everything that was lost.

Some consequences of climate change unfold over very long timescales.

Sea levels, for example, respond slowly to warming and can continue rising even after global temperatures stop increasing. Ecosystems and species lost because of climate change may not return simply because temperatures eventually decline.

The report also highlights concerns surrounding potential climate tipping points.

These include instability in major ice sheets, changes affecting the Amazon rainforest and disruption of the Atlantic Meridional Overturning Circulation, or AMOC.

Scientists continue to study the precise risks and thresholds associated with these systems, but the concern is that some changes could become difficult or impossible to reverse once critical conditions are reached.

Cutting fossil fuel emissions remains the first priority

Bringing temperatures down after an overshoot would require much more than simply slowing the growth of emissions.

UNEP emphasizes the need for rapid and deep reductions in greenhouse gas emissions, including a faster shift away from fossil fuels and substantial cuts in methane emissions.

Reaching net-zero emissions as quickly as possible would be essential.

But if humanity wants global temperatures to decline rather than merely stabilize, emissions would eventually need to fall below the amount of greenhouse gases being removed from the atmosphere.

That is where the concept of net-negative emissions comes in.

Why carbon removal could become more important

Carbon dioxide removal could play a role in bringing temperatures down after an overshoot.

This could include natural approaches such as restoring forests as well as technological methods such as direct air capture, which seeks to extract carbon dioxide directly from the atmosphere.

However, UNEP makes an important distinction: carbon removal cannot be used as an excuse to delay emissions cuts.

Removing carbon from the atmosphere is difficult, expensive and limited in scale. Even under ambitious deployment, carbon removal by itself would only be capable of reducing global temperatures by a fraction of a degree over this century.

The priority therefore remains straightforward: prevent as much greenhouse gas from entering the atmosphere as possible in the first place.

The climate clock does not stop at 1.5°C

The biggest change in the UN's assessment is perhaps the way the 1.5°C threshold is viewed.

For years, the number was often presented as a line humanity had to avoid crossing. The emerging reality is more complicated.

If the world does cross the threshold, every tenth of a degree avoided beyond it could still mean fewer risks, less environmental damage and greater protection for vulnerable populations.

The task, therefore, is not to treat 1.5°C as a lost cause.

It is to prevent a temporary overshoot from becoming a much larger and longer-lasting one.

The choices governments make now will determine whether warming peaks close to the threshold or continues toward far more dangerous levels.

Crossing 1.5°C may become unavoidable, but how high Earth ultimately warms is still not predetermined.