Why the UNEP 1.5°C overshoot report must be an urgent call to action on climate change

The United Nations Environment Programme (UNEP) has warned us that the global temperature will rise above 1.5°C, likely within the next few years, to levels that will worsen extreme weather impacts and intensify the risks of climate change. This is why Greenpeace is demanding that governments urgently respond by rapidly transitioning away from fossil fuels and ending forest destruction to minimise the threat.

Despite this temporary overshoot, the global agreed commitment remains limiting warming to 1.5°C, as outlined in the Paris Agreement and upheld by the International Court of Justice and adopted at the UN General Assembly.

The UNEP's new report 'Limiting Overshoot' outlines a pathway called "overshoot, peak and decline" to minimise and adapt to the impacts of an exceedance and an eventual return to 1.5°C. But even in the best case scenario where governments fully implement and exceed their current and future climate action plans, the UNEP states that our temperature rise will still hit 1.8°C before declining.

The UNEP stresses there are "no good outcomes if we remain above 1.5°C" and that we must focus on making the overshoot as small and short as possible. This will be determined by decisions taken today - rapid climate action across all sectors is "both necessary and feasible" to hold warming as close to 1.5°C by 2100.

With a symbolic red line between the village of Lützerath and the Garzweiler opencast lignite mine in North Rhine-Westphalia, Greenpeace activists are protesting against the destruction of the village by the coal company RWE.

What does an overshoot of 1.5°C actually mean?

In 2015, at the UN climate conference COP21 in Paris, close to 200 governments committed to efforts aimed at limiting global warming to 1.5°C and well within 2°C by 2100.

While the average global temperatures rose above target for the first time in 2024 - hitting 1.6°C above the pre-industrial period - this did not signify a long-term breach of the 1.5°C limit. One year is only a single indicator and what matters is the long-term trend - measured as a temperature increase over decades, not individual months or years.

The term 'overshoot', however, is increasingly being used to describe future temperature trends that temporarily exceed 1.5°C and are followed by future declines. Overshoot, peak and decline pathways are part of the new set of global emissions scenarios which will provide the basis for upcoming climate research reports from the Intergovernmental Panel on Climate Change (IPCC), the UN's climate science panel.

What does the UNEP report say about avoiding a 1.5°C overshoot?

The UNEP said global action to cut greenhouse gas emissions had been too slow to stop temperatures rising more than 1.5°C in "the next few years".

In terms of the planetary carbon budget, only about 130 Gt of additional CO₂ can be emitted from 2026 onwards to have even a 50% chance of limiting global warming to 1.5°C. To stay within this budget, CO₂ emissions would need to decline steadily from 2025 levels to zero in just over six years, leaving us with a huge emissions gap between current levels and what is needed.

So, after decades of "insufficient action", the UNEP outlined three challenges to limiting temperature overshoot:

• Reducing emissions and addressing impacts
• Limiting peak warming and managing climate risks
• Sustaining the decline in temperatures and scaling up adaptation efforts

The UNEP called for a global response that includes the three interconnected phases. An immediate response for slowing temperature rise, involving deep emission cuts and urgent measures to protect vulnerable populations. Secondly, a coping and containment phase focusing to boost climate resilience needs, followed by a third phase that focuses on building long-term resilience with net-negative emissions.

What's required, it added, was multilateral cooperation, climate finance and effective implementation of government policies to accelerate the transition away from fossil fuels and to expand renewable energies, cut methane pollution and protect land, forest and oceans.

What are the consequences of a 1.5°C overshoot?

The UNEP said that by delaying action we might lose the chance to return to 1.5°C and "face an unprecedented, damaged world". The impacts of a 1.5°C overshoot would be wide and varied, affecting ecosystems, human systems and economic systems.

The repeated heatwaves and wildfires among the so-called natural disasters in 2026 are also the types of impacts we've been warned about. A potential world of 1.5°C overshoot will see these types of disasters become more likely and potentially more severe in years to come.

Cryosphere impacts such as Arctic sea ice and habitat loss, glacial loss, permafrost thaw and degradation will be on the frontline and these impacts will affect ecosystems and downstream communities dependent on seasonal melt water.

The Blomstrandbreen glacier in NY Alesund, Svalbard.

Loss of biodiversity in marine and terrestrial fronts from land use change and ocean acidification will trickle down to human health, food and water security as cities and infrastructure come under "increasing strain" from extreme events and other impacts.

The UNEP also warned that some Small Island Developing States (SIDS) and low-lying coastal cities could become partially or completely submerged due to sea level rise. This could put continuity of their statehood itself in question.

All of these, among others, will mean that societies have to adjust constantly, raising issues of justice, power, and political legitimacy.

How close are we to the 1.5°C overshoot threshold?

While the WMO has warned it's very likely the global temperature will temporarily exceed 1.5°C for at least one year between 2026 and 2030, it has also said that it's likely the 2026-2030 five-year average will exceed 1.5°C.

Now, the UNEP said human-induced global warming is nearing 1.4°C, and global temperatures have been increasing at about 0.25°C per decade (with some recent studies showing an even faster rate).

As per the IPCC, every five years of high emissions adds 0.1°C to peak warming. Based on these trends, global warming could reach 1.5°C within a few years - around the end of this decade.

Will 1.5°C overshoot trigger irreversible tipping points?

There is a chance some impacts from a 1.5°C overshoot will be irreversible even if global temperatures eventually decline. The risk of tipping points increases the higher global temperatures reach, and the longer we stay above 1.5°C so it's important to restrict this rise as much as possible.

Irreversible changes include the potential destabilisation (i.e. melting and collapse) of the major West Antarctic and Greenland ice sheets and degradation of the Amazon rainforest, and disruption of the Atlantic Meridional Overturning Circulation (AMOC) - the system of ocean currents which help regulate the climate by moving warm surface water north and cold deep water south.

These are changes that "would reshape the world forever" and may emerge abruptly or accumulate over time, the UNEP warned. A fall in global temperature may also co-exist, for example, with a continuation of impacts - continued sea level rise, ocean warming, cryosphere losses and regional changes in rainfall, drought and weather extremes.

During a field activity with Kayapó leaders, Greenpeace Brazil launched a global campaign in defense of the Amazon, which joins forces with other organizations worldwide.

Placing equity and justice at the core of the global response to climate change

The UNEP report strongly recognised that equity and justice must be a central element of strategies to protect vulnerable people from climate change and to create a just transition for communities and workforces as part of efforts aimed at securing a liveable future for all.

Ultimately, developed countries have an historical responsibility and capability to act the "hardest and fastest". They must ensure that a just transition away from fossil fuels allows all communities to access the benefits of renewable energy and that no one is disadvantaged through the transition.

As Greenpeace International explains in its policy briefing, a just transition is more than simply swapping coal, oil and gas for renewables. It is an opportunity to transform energy, transport, industrial and other systems so they are more secure and affordable, reduce inequality, protect ecosystems and shift power from elites and multi-billion-dollar corporations to people.

What climate mitigation actions need to take place, and how important is adaptation?

While the UNEP report emphasised an urgent need for climate action to limit the overshoot, it recognised that impacts are unavoidable and that a combination of mitigation (climate action) and adaptation will be needed.

Mitigation and adaptation are "fundamentally interconnected", the UNEP said, adding that mitigation will determine the scale and duration of future climate risks, and adaptation remains essential because impacts are already happening and additional warming is unavoidable.

Mitigation determines the journey and the destination, and adaptation determines who gets there. There should be commitments on finance, durable solidarity and inclusive governance built well before peak warming, rather than waiting to be improvised under crisis conditions.

A long fire line burns along a pine forest under a column of dark smoke during a wildfire in Marcheprime in Gironde, France.

If we overshoot 1.5°C, how can we get back to that limit?

Net-zero - where CO₂ emissions are balanced by CO₂ removals - is required to halt warming, along with deep reductions in methane and other short lived climate pollutants. It is essential that early climate action is taken to limit the peak temperature rise because the higher the temperature rises, the greater amount of CO₂ needs to be removed from the atmosphere.

Deep cuts in methane are also vital because it contributes about 0.5°C of current global warming. While UNEP said there are challenges in tackling methane emissions, it's clear we cannot cool the planet while industrial livestock production continues to expand unchecked, driving superheating methane emissions, deforestation, drinking water pollution, and extinction.

According to the UNEP's analysis, some level of carbon dioxide removal (CDR) will also be necessary. However, most CDR strategies remain highly uncertain when it comes to effectiveness, scalability, permanence, durability, potential adverse impacts and social acceptability.

What needs to be done now to avoid or limit a 1.5°C overshoot?

On the road to the UN General Assembly in September and the UN climate conference COP31 in November, governments must acknowledge this report and signal their intent to accelerate a just transition. The 1.5°C limit is a legal, political and moral obligation, and what matters now is what we do today and tomorrow because every fraction of a degree matters.

Essential actions to take now are:

• Immediate and profound emissions cuts as part of a Just Transition away from fossil fuels are urgently needed,
• Protecting the oceans and forest
• Protecting the most vulnerable and those least responsible for climate change

A stable climate in the future requires change today!

Jasper Inventor is Deputy Programme Director at Greenpeace International.
Dr. Jerry Jose is Senior Scientist at the Greenpeace International Science Unit (University of Exeter, UK).