The 1.5°C Global Warming Threshold Is Slipping Away: What Does UNEP Say Happens Next?

The 1.5°C Global Warming Threshold Is Slipping Away: What Does UNEP Say Happens Next?

KAKALI DAS

For more than two decades, the world has been trying to stay away from a number: 1.5 degrees Celsius.

It was never just a number. It represented a boundary that scientists, policymakers and climate campaigners repeatedly warned the world not to cross. Beyond it, the risks of irreversible damage to ecosystems, livelihoods and human societies would increase sharply.

Countries came together, negotiated agreements, announced targets and promised to reduce emissions. The idea was to keep global warming below 1.5 degrees Celsius above pre industrial levels and, in doing so, avoid the worst consequences of climate change.

But that carefully drawn line is now becoming increasingly difficult to protect.

The latest assessment from the United Nations Environment Programme (UNEP) suggests that a breach of 1.5 degrees Celsius is becoming unavoidable. The world is moving towards what scientists describe as an overshoot, a period in which global temperatures rise above the 1.5 degree threshold before potentially declining again.

The word “overshoot” may sound reassuring. It suggests that crossing the line does not necessarily mean staying there forever. Temperatures could eventually come down if humanity manages to reduce greenhouse gas emissions dramatically and remove large amounts of carbon dioxide from the atmosphere.

But there is a catch.

The longer the world remains above 1.5 degrees Celsius, the greater the damage could become. And some of that damage may never be reversed, even if global temperatures eventually fall.

That is what makes the present moment so important. The question is no longer only whether the world can prevent 1.5 degrees Celsius from being crossed. It is about what happens after the crossing, how high temperatures rise, how long they stay there and how much damage humanity can prevent along the way.

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The safest pathway that the world once hoped to follow is already slipping away. What lies ahead is likely to be more difficult than what governments had originally planned for.

The range of possible futures is becoming increasingly clear. Under the best possible circumstances, with countries making the strongest efforts available, warming could potentially be limited to around 1.8 degrees Celsius. Under a much worse scenario, where climate action slows down or political commitment weakens, global temperatures could exceed 2 degrees Celsius.

The difference between these futures is not simply a matter of statistics. It represents a difference in the intensity of heat waves, pressure on water and food systems, biodiversity loss, damage to infrastructure and economic disruption.

There is another important part of this picture: time.

Imagine global temperatures rise above 1.5 degrees Celsius and eventually begin to decline. That decline would not happen overnight. It could take decades. During those decades, ecosystems, communities and economies would continue to operate in a warmer world.

A shorter overshoot would mean less time for these pressures to accumulate. A longer overshoot could mean much more severe and widespread consequences.

And even when temperatures eventually come down, the world would not necessarily return to where it was before.

Some damage can be reversed. Some cannot.

An ecosystem that has collapsed may not simply rebuild itself because global temperatures fall later. Species that become extinct cannot be brought back. Communities that lose their homes and livelihoods cannot always recover what they have lost. Climate impacts can accumulate even when the global temperature itself begins to decline.

The objective, therefore, is not to pretend that nothing can be done because 1.5 degrees Celsius may be breached. The objective is to make the overshoot as small and as short as possible.

That will require a significant change in the way the world thinks about emissions.

For years, net zero has been the central goal. The basic idea is that the amount of greenhouse gases released into the atmosphere should eventually be balanced by the amount removed from it.

But an overshoot scenario demands more. The world will eventually have to move towards net negative emissions, meaning that more carbon dioxide is removed from the atmosphere than is being emitted.

This is where carbon dioxide removal, or CDR, becomes increasingly important. Carbon dioxide removal refers to methods of taking carbon dioxide out of the atmosphere and storing it through natural or technological processes.

But CDR cannot become a substitute for cutting emissions. The world cannot continue releasing huge quantities of greenhouse gases and assume that future carbon removal technologies will solve the problem. Emissions reductions and carbon dioxide removal have to work together.

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The more rapidly emissions fall, and the greater the amount of carbon dioxide that can safely and effectively be removed, the greater the possibility of limiting the duration of the overshoot.

Yet this brings the discussion back to an uncomfortable question.

Why are we having this conversation at all?

The world did not suddenly discover climate change. The warning has been around for decades. Scientists have repeatedly explained the consequences of continued greenhouse gas emissions. Governments have known about the risks. International negotiations have taken place for years.

And still, emissions continue to rise.

One of the clearest reasons can be found in something that surrounds almost every part of modern life: fossil fuels.

Coal, oil and gas remain deeply embedded in global economies and industrial systems. They power electricity generation, transport, manufacturing and a wide range of economic activities. Renewable energy has grown rapidly, but the global energy system has not yet moved away from fossil fuels at the speed required.

The result is visible in the numbers.

Global greenhouse gas emissions reached more than 57.7 gigatonnes in 2024, an increase of around 2.4 percent from the previous year.

Behind that number lies a familiar contradiction. The world is talking about reducing emissions while continuing to build economic systems that depend heavily on the fuels responsible for those emissions.

Climate policy has struggled with the same contradiction.

Governments have announced targets and submitted climate plans, but the combined effect of existing policies remains far from the pathway required to limit warming to 1.5 degrees Celsius. Even if current policies are fully implemented, UNEP has indicated that the world could still be heading towards around 2.8 degrees Celsius of warming by 2100.

That is a considerable gap between ambition and reality.

The history of climate negotiations shows just how long this gap has existed.

The Kyoto Protocol, adopted in 1997, established binding emission reduction targets for developed countries. It was an important step, but its coverage was limited because developing countries were not subject to the same binding targets.

Then came the Copenhagen climate conference in 2009. The 2 degree Celsius goal was recognised, while 1.5 degrees Celsius was increasingly understood as the safer objective because of the severe and potentially irreversible damage associated with higher warming.

In 2015, the Paris Agreement brought the 1.5 degree Celsius goal to the centre of global climate policy. Countries agreed to keep the rise in global average temperature well below 2 degrees Celsius while pursuing efforts to limit it to 1.5 degrees Celsius.

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Nationally determined contributions, or NDCs, became one of the central mechanisms of the agreement. Each country would determine its own climate commitments and strengthen them over time.

It was an approach designed to bring countries together while recognising their different economic and national circumstances.

But it also exposed one of the fundamental difficulties of climate politics.

Every country has its own development priorities.

Governments want economic growth, jobs, energy security and improved living standards. Developing countries, in particular, argue that they need the resources to develop while also dealing with a crisis that they did not create to the same extent as wealthy industrialised nations.

The result is a difficult balancing act between development and environmental protection.

Even countries that have made progress towards their climate commitments cannot solve the problem alone. Climate change is cumulative and global. The atmosphere does not distinguish between emissions from one country and emissions from another.

This is why national progress, although important, does not automatically translate into global progress.

The problem becomes even more difficult when finance enters the picture.

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A developing country may want to move away from coal, expand renewable energy, improve public transport, strengthen its electricity grid and protect vulnerable communities from climate impacts. But each of those transitions requires money, technology and institutional capacity.

The Glasgow climate conference in 2021 brought this challenge into sharp focus. Countries strengthened their commitments for action by 2030 and agreed to work towards reducing unabated coal use. But questions remained over how developing countries would finance the transition.

The climate crisis, therefore, is also a crisis of inequality.

The countries and communities that are most vulnerable are often not those that have contributed the most to historical emissions. This is particularly visible across the Global South.

The Global South broadly refers to countries that have historically experienced lower levels of economic development and, in many cases, colonial exploitation. Many of these countries now face high exposure to climate impacts while having fewer resources to adapt.

For millions of people, climate change is not an abstract discussion about global temperature targets. It is a question of whether crops will survive the season, whether fishing will remain possible, whether drinking water will be available, whether homes will withstand floods and whether livelihoods can continue.

Agriculture and fisheries are particularly vulnerable because they depend directly on natural systems. Rising temperatures, changing rainfall patterns, floods, droughts and other extreme events can quickly become economic crises for communities that depend on these sectors.

Lower adaptive capacity makes the problem worse.

A wealthy country may be able to spend billions on flood protection, heat management, infrastructure or disaster recovery. A poorer country may not have the same financial space.

This is where climate change can become development reversal.

Years of progress can be wiped away by a single major disaster. Repeated disasters can make recovery increasingly difficult. Governments that should be investing in education, healthcare and infrastructure may instead have to spend more and more on rebuilding after climate related events.

And these impacts are no longer distant possibilities.

Across different parts of the world, the warning signs are already visible. Europe has experienced severe heat waves. Assam has faced devastating floods. Nepal has experienced flooding and extreme weather. Brazil and parts of Africa have also faced major climate related disasters.

The geography may be different, but the underlying story is increasingly familiar: heat, water, food, ecosystems, livelihoods and economies are becoming connected through a changing climate.

The world is therefore entering a difficult period. The breach of 1.5 degrees Celsius, if it becomes established, will not mark the end of climate action. It will mark a new phase of it.

The target may no longer be simply to prevent the crossing. The task will be to limit how far temperatures go beyond it, how long they remain there and how much irreversible damage occurs during that time.

But perhaps the most uncomfortable lesson is that much of this was foreseeable.

The world had the scientific evidence. It had the conferences. It had the agreements. It had the targets.

What it did not have was enough action.

For more than two decades, governments have repeatedly promised to reduce emissions. Yet fossil fuels remain deeply embedded in the global economy. Greenhouse gas emissions continue to rise. Climate policies remain insufficient. Developing countries continue to struggle with finance and technology gaps, while political commitment in wealthier countries remains uneven.

The question now is not simply whether the world failed to protect the 1.5 degree Celsius threshold.

The larger question is who will pay for that failure.

The costs will not be distributed equally.

Some countries will have greater financial capacity to adapt. Others will face rising debt as they rebuild after disasters. Some communities will lose their homes. Farmers may lose crops. Fishers may lose access to productive waters. Ecosystems may cross points from which recovery is impossible.

The people who contributed least to the problem may end up paying some of its highest costs.

That is why the conversation around 1.5 degrees Celsius cannot be reduced to a debate about temperature targets. Behind the number are questions of responsibility, finance, development and justice.

There is still a choice in front of the world.

The crossing of 1.5 degrees Celsius does not mean that every future outcome has already been decided. There is a vast difference between a short overshoot and a prolonged period of much higher warming. There is a difference between 1.8 degrees and more than 2 degrees. There is a difference between rapid emission reductions and continued dependence on fossil fuels.

Every fraction of a degree still matters.Every year of delayed action matters. Every tonne of greenhouse gas emissions avoided matters.

The world may be losing the possibility of keeping 1.5 degrees Celsius permanently within reach. But it has not lost the ability to decide what happens next.

The challenge is now to reduce emissions as rapidly as possible, move away from fossil fuels, expand renewable energy, strengthen climate adaptation, close the finance gap and responsibly develop carbon dioxide removal.

The longer the world waits, the longer the overshoot could last and the more damage could become permanent.

The real story of 1.5 degrees Celsius, then, is not simply about a line that humanity may cross.It is about what humanity chooses to do after crossing it.

For years, the question was whether we could prevent the threshold from being breached.Now the question is harder.

How much higher will we allow the temperature to go, how long will we allow it to stay there, and who will bear the cost of our delay?

Those are no longer questions for the future.They are questions for today.

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