Governments have failed to limit climate warming to 1.5°C. What now?

A sobering new UN report confirms that we can no longer avoid overshooting 1.5°C of warming, considered by scientists to be a dangerous threshold. The authors stress that we must aim to return below this level before 2100, and lay out recommendations for accelerating mitigation and adaptation efforts.

A sobering summer

This summer once again broke new heat records and gave the world a taste of what a climate apocalypse might look like. Back-to-back heatwaves in Europe are estimated to have caused at least 35,000 excess deaths. Flash floods in Nepal following the collapse of a Himalayan glacier on August 26 have so far resulted in more than 1,000 confirmed deaths. In July, more than 100 million Americans were under dangerous air quality warnings due to smoke from wildfires burning across Canada.

This year made it especially clear that nowhere is safe from the climate crisis, yet world leaders are still failing to mount an appropriate response.

The new report

Limiting Overshoot: Navigating exceedance of 1.5°C and pathways towards return, a new report by the United Nations Environment Programme (UNEP), underscores this failure, explaining that we will likely exceed 1.5°C of warming relative to pre-industrial levels by 2030.

The report states:

“The world must get onto an ‘overshoot, peak and decline’ pathway that holds temperature rise to the lowest level possible, then brings it down by the end of the century, all while taking adaptation actions that reduce vulnerability to the current or expected impacts of climate change. This is by no means an acceptable or preferred pathway; it is simply the best remaining option.”

Note: At Population Connection, we generally use the term ‘overshoot’ in reference to ecological overshoot, defined as using up natural resources at a faster rate than they can be regenerated. This UNEP report uses overshoot to describe a multidecadal exceedance of a specified global warming level, in this case, 1.5°C.

A decade of failure

Governments agreed to limit warming to “well below 2°C” and ideally to no more than 1.5°C under the landmark 2015 Paris Agreement, which was at the time hailed as a huge international policy victory. Unfortunately, 11 years later, global greenhouse gas emissions are still increasing, and human-caused global warming is now already close to 1.4°C (based on a 20-year average) above pre-industrial levels. The past 11 years have been the warmest ever recorded, and in 2024, global mean temperatures were as much as 1.55°C higher than the pre-industrial average.

If we continue on current trends, the remaining carbon budget for limiting warming to 1.5°C would be exhausted in three years, while staying within this budget would require reaching zero global CO₂ emissions in just over six years.

The UNEP report warns that current policies put us on track for median global warming of around 2.6°C by 2100. Even under one of their most optimistic scenarios, which assumes full implementation of all current government emissions pledges as well as long-term net zero targets, peak warming would reach around 1.8°C.

Despite the inevitability of overshoot, the authors emphasize that the goal must still be to limit warming to 1.5°C, but that it must now be “approached from above while the world adapts to intensifying climate impacts.” They stress,

“Every fraction of a degree avoided and every year by which overshoot is shortened will save lives, protect ecosystems and reduce economic losses.”

According to the Intergovernmental Panel on Climate Change (IPCC), the global scientific authority on climate change, every additional five years of sustained high emissions adds approximately 0.1°C to peak warming.

The harsh reality of a warmer world

Further warming will cause more extreme weather events, biodiversity and ecosystem loss, and sea-level rise, while human health and food and water security will also be increasingly compromised. At the same time, the risk of triggering catastrophic tipping points is growing. These are large-scale, irreversible changes that would reshape the world forever, such as the collapse of the West Antarctic and Greenland ice sheets, the shut-down of the Atlantic Meridional Overturning Circulation (AMOC), and a massive dieback of the Amazon rainforest.

Many of these impacts would in turn accelerate warming, causing a disastrous runaway effect. For example, the loss of surface ice, which reflects sunlight back into space, increases Earth’s absorption of warming solar radiation, while the collapse of major forests like the Amazon and widespread melting of permafrost would release billions of tons of carbon dioxide into the atmosphere.

The report repeatedly highlights that the urgency to act is greater than ever before. Ramping up mitigation efforts is critical to lessen the scale and duration of climate overshoot and impacts, while accelerating adaptation is required to limit loss of lives and livelihoods under existing levels of warming as well as unavoidable additional temperature increases.

Prolonged failure to act risks undermining both mitigation and adaptation efforts because funding will increasingly be diverted towards disaster relief, creating a vicious feedback loop.

Carbon removal required

Cutting emissions alone will no longer cut it — governments’ delay and lack of ambition mean that the only way we can now achieve a return to below 1.5°C is by actively removing carbon from the atmosphere. The report explains that there are two forms of carbon dioxide removal (CDR): conventional, such as afforestation and ecosystem restoration (sometimes called “nature-based solutions”), and novel, which includes carbon capture and storage technologies. Conventional removal is vastly preferable because novel methods have not yet been developed at a meaningful scale, are far more expensive, and carry a high risk of unintended negative consequences.

While CDR will be required to fix the 1.5°C overshoot, the authors warn that warming will take many decades to reverse. The report urges governments to still prioritize rapidly reducing emissions and to avoid over-relying on CDR, as even optimistic CDR scaling will likely not be able to deliver more than a few tenths of a degree of temperature decline this century.

Early intervention is key:

“In a warmer future, nature’s removal and carbon retention capacity will likely be eroded, while competition between sustainable development goals and CDR can limit the feasibility of land-intensive mitigation strategies.”

Indeed, CDR requires vast amounts of land, which would then become unavailable for other uses, such as farming. But demand for agricultural land will continue to increase as human populations and consumption levels grow.

Population action is climate action

This is where the report falls short. It doesn’t acknowledge that continuing on our current population growth trajectory will make it increasingly difficult to minimize and end climate overshoot — our global population of 8.3 billion is projected to grow by another two billion people or so before the end of the century.

Most of that growth will occur in the regions with the lowest per capita consumption, but the cumulative effect, combined with rapid industrialization in emerging economies, will be massive. According to the IPCC,

“Globally, GDP per capita and population growth remained the strongest drivers of CO₂ emissions from fossil fuel combustion in the last decade.”

Unfortunately, the welcome trend of declining poverty in low-income regions also translates into increases in demand for food (including the most environmentally problematic ones like meat and dairy), energy, and resources.

Ending population growth as quickly as possible by removing barriers to family planning and girls’ education is also key for climate adaptation. A report by Population Institute published in July showed that populations in the 80 countries most vulnerable to climate change impacts are growing twice to three times as fast as the global average. This means more lives exposed to disasters and more pressure on already limited resources, fragile infrastructure, and overstretched services.

Advancing gender equality and improving access to reproductive health services is critical from a human rights perspective, and incredibly urgent from a climate crisis perspective.