September 2, 2026

expert reaction to UNEP report on overshooting 1.5C

experts comment on a United Nations Environment Programme report on overshooting 1.5C

Prof Richard Betts, Chair in Climate Impacts at the University of Exeter, said:

“Global warming will cross 1.5C in the next few years, so we now need to work hard to limit the damage. We urgently need to increase adaptation and resilience, especially to protect the most vulnerable people and ecosystems, and it remains critical that we bring emissions to net zero to limit warming to as little as possible above 1.5C and give us a chance of lowering temperatures again. Actively removing carbon from the atmosphere will also be needed, but crucially this is as well as reducing emissions, not instead.”

Quotes gathered by the Spanish SMC:

Raffaele Bernardello, a researcher with the Climate Variability and Change group at the Barcelona Supercomputing Centre (BSC), says:

“This report explicitly acknowledges the inevitability of crossing the 1.5 C warming limit, set by the Paris agreement, within the next few years. At the same time, the report stresses how the duration and intensity of a so-called overshoot period must be limited to reduce risks of harm to humans, ecosystems, infrastructure and economies. Every fraction of a degree and every year above 1.5 C matters and both should be minimized. The report delineates three interconnected phases that should drive an overshoot peak and decline pathway. These are immediate response, coping and containment, and long-term resilience and they would coexist across regions and timescales. The report stresses the urgency of planning mitigation and adaptation as interconnected dimensions of the same problem rather than sequential stages.

“The report sounds once again the alarm about the urgency of rapid action to reduce the most severe impacts of climate change and it provides a detailed account of what is required and what are the potential consequences of further delaying global coordinated action.”

He has not declared any conflicts of interest.

Ernesto Rodríguez, senior state meteorologist and president of the Spanish Meteorological Association, says:

“We are approaching an observed increase in the global average temperature of 1.5 °C compared with the pre-industrial period, as set out in the Paris Agreement as a policy objective — not to exceed that 1.5 °C temperature rise — in order to avoid the undesirable consequences of current climate change. According to estimates by the World Meteorological Organisation (WMO), this 1.5 ºC rise could be reached as early as this decade. Once this limit has been exceeded (overshooting), in order to continue to maintain the 1.5 ºC warming target, a strategy would need to be devised that asymptotically approaches this limit from above the trend line, rather than from below as was initially envisaged. This strategy must be based on swift, collective and global action to reverse the trend in global temperature and achieve the 1.5 °C target by the end of the 21st century.

“The current report, based on the IPCC’s findings, paints a picture that remains both feasible and hopeful, provided that the overshoot of the 1.5 °C limit does not exceed a few tenths of a degree (0.2–0.3 °C) and is limited in duration. To reverse the temperature trend, the ultimate goal of net-zero greenhouse gas (GHG) emissions would need to be revised and treated as an interim target on the path to net-negative emissions, leading to the removal of GHGs from the atmosphere. This will only be achieved through the large-scale implementation of methods for removing or eliminating atmospheric CO₂, whether based on reforestation, afforestation (planting trees in areas where there has historically been a forest), ecosystem restoration, or on unconventional techniques such as, for example, bioenergy generation combined with carbon capture and storage. Of course, the large-scale removal of atmospheric CO₂ is in addition to urgent mitigation – which involves phasing out the use of fossil fuels and replacing them with renewable energy sources – and to adaptation, which is particularly necessary in regions and communities where the negative effects of climate change are already being felt.

“In short, it is not so much a question of changing the long-term target itself of 1.5 °C warming compared with the pre-industrial period, but rather of approaching it asymptotically from above the global temperature trend curve through ambitious policies for urgent mitigation and the widespread deployment of a mix of techniques for removing atmospheric CO₂. The use of techniques to remove atmospheric CO₂ must never be seen as a substitute for the urgent reduction of GHG emissions, but rather as supplementary to this reduction; otherwise, it would amount to passing the problem on to future generations”.

He has not declared any conflicts of interest.

Quotes gathered by the New Zealand SMC:

Andy Reisinger, Honorary Associate Professor, Australian National University, and lead author of the report’s chapter on mitigation, comments:

“This is the first report by a United Nations agency that says unambiguously that we will cross 1.5°C in the next few years, given insufficient actions to reduce greenhouse gas emissions.

“It’s a wake-up call to governments and industry to confront this reality, but not a reason to give up on 1.5°C as a long-term goal. The failure to reduce emissions has increasingly dangerous and disruptive consequences around the world, in the form of significant heat-related deaths, flooding, disruption to food production and economies, ice loss in mountain and polar regions, and repeated mass bleaching of coral reefs. These losses and damages will escalate further and often land hardest on the shoulders of those least responsible for those mounting risks.

“Adapting to climate change clearly must become a greater focus, but there are limits to how much adaptation can prevent. At the same time as dealing with increasing climate-related disasters, the world therefore needs to accelerate efforts to reduce emissions of all greenhouse gases and reach at least net-zero CO₂ emissions globally by mid-century.

“We know how to and can still do this. This would halt global warming as close to 1.5°C as is still possible and keep at least some of the risks manageable. More importantly, the report emphasizes that the long-term goal remains to return to 1.5°C, as indeed governments reaffirmed only last year. Bringing global warming back down will be challenging and complex but is possible, provided that governments and industry begin to think and act beyond current net-zero targets.

“As the report says, this is by no means an acceptable or preferred path to take, but is by now simply the best remaining option.”

Conflict of interest statement: “I’m an author of several parts of the report but have received no funding for this work. I’m a member of He Pou A Rangi, New Zealand’s Climate Change Commission, but my input to the report and my comments reflect my personal views and insights only.”

Dr Nicholas Cradock-Henry, Principal Social Scientist, Earth Sciences New Zealand, comments:

“The evidence is clear; it is now almost certain the world will warm past 1.5°C, requiring transformational changes to dramatically reduce global greenhouse emissions, and adapt to the inevitable adverse consequences. While sobering, UNEP’s report on limiting overshoot (which will complement forthcoming outputs from the IPCC’s 7^th Assessment, with a Special Report on Cities due early 2027, followed by reports from Working Groups 1-3, through to 2029), represents climate science at its best; weighing the breadth and depth of scientific literature; providing clear-eyed assessment; and delivering policy-relevant information for decision-makers. The scientists have done their work.

“This departure from historical climate baselines will manifest through changes in temperature, rainfall, frequency and severity of extremes that will exceed the capability and capacity of many social and economic systems to cope. Agriculture and food security, water availability, human health and livelihoods, will be impacted. Furthermore, these effects will not be evenly distributed, falling disproportionately on marginalised, Indigenous, and vulnerable populations worldwide who possess the least capacity to cope.

“For Aotearoa New Zealand, the report provides another reminder of our own exposure, and need for greater resilience.

“First, as a globally connected trading nation, international supply chain shocks, shifting marine ecosystems, and geopolitical tensions will be exacerbated. This will have material effects on our economy.

“Second, we must incorporate overshoot into adaptation planning, now. Prudent risk management dictates that we cannot afford to dismiss tail-risk extremes. Rather, we must account for the compounding and cascading impacts of changing hazards to safeguard our long-term agricultural productivity and interconnected infrastructure.

“Finally, we must act. We will not be unaffected. This will require a coordinated, all-of-society approach to respond immediately, acknowledge the true scale of the challenge, and mobilise a comprehensive response. We must simultaneously reduce emissions and accelerate adaptation, cope with and contain unavoidable losses, and embed resilience as a national priority.

“Resilience is not a luxury; it is a necessity we can no longer afford to ignore. It is essential for safeguarding wellbeing and securing a sustainable, prosperous, and equitable future for all.”

Conflict of interest statement: “Dr Cradock-Henry is the Programme Lead of the Endeavour Fund for the ‘Accelerating Adaptation to Climate Change’ programme (2025–2030). He is a Lead Author for Working Group II of the Intergovernmental Panel on Climate Change (IPCC) Seventh Assessment Report.”

Dr Sam Dean, Chief Scientist – Future Climate, Earth Sciences New Zealand, comments:

“As this report emphasises, in the next few years the Earth will exceed the warming threshold within the Paris agreement of 1.5°C above preindustrial. It is also looking unlikely that we will be able to stay below 2°C given our global progress to date on reducing emissions in the face of growing economic production. This report considers what an overshoot looks like, one where we manage to return back to our current warming level by 2100.  The likely impacts on ecosystems, hazards and societal health are outlined; with these being both complex and confronting. Practically, climate change will infiltrate and impact our lives on an ever more regular basis, almost certainly throwing in a few surprises along the way.
 
“The report also highlights the levels of co-ordinated international mitigation effort that would be required to limit the overshoot to 70 years (with a peak of 1.7°C), including the significant negative emissions that will be needed beyond carbon-zero. In this context, it is important to recognise that net zero carbon is unlikely to represent the end point of our mitigation journey, but rather an early milestone on the path to restoring global temperatures. While we can remain hopeful about the future, we must consider what the unique consequences of climate change will be and how we best prepare for them.”

Conflict of interest statement: “Dr Dean is the Chief Scientist for Future Climate at Earth Sciences New Zealand. He has worked extensively on the projections of climate change impacts on Aotearoa New Zealand and was a contributing author for Working Group II of the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report.”

Dr Scott Nodder, Principal Scientist at Earth Sciences NZ, comments:

“The Limiting Overshoot report is a timely reinforcement of the importance of responding appropriately to the climate crisis by reducing greenhouse gas emissions.

“The report also considers Carbon Dioxide Removal (CDR) techniques, such as afforestation and bioenergy with carbon capture and storage, as mitigation approaches to limit the exceedance of the 1.5°C planetary threshold. The IPCC states that CDR is necessary to mop up legacy carbon and offset the hard-to-abate emissions of transport and cement production. CDR technologies, however, should not be viewed as an ‘easy’ option to negate our obligations to drastically reduce, if not eliminate, greenhouse gas emissions, especially if we are to meet net-zero by 2050. This is reflected in the UNEP report, which is explicit in outlining the socio-economic and environmental consequences if this aim is not achieved.

“The oceans are a large reservoir of carbon (~60 times greater than the atmosphere) with potential for increased removal by marine CDR (mCDR). These techniques involve enhancing natural chemical (e.g., ocean alkalinity enhancement) and biological (e.g., ocean nutrient fertilization, macroalgae growth and burial) processes.

“However, research and development of mCDR lags terrestrial CDR, reflecting the difficulty of evaluating effectiveness, risks and permanence in a highly dynamic ocean. Ecosystem response to mCDR deployment at scale is currently uncertain. In addition, robust baselines and monitoring and verification techniques are needed to confirm additional carbon removal, and there is a lack of governance and societal understanding for mCDR. Even if the benefits outweigh the risks, it is unlikely that mCDR could be deployed at scale for at least a decade, and consequently it is not an immediate solution to the 1.5°C overshoot.”
 
Conflict of interest statement: “Scott Nodder co-leads an MBIE Endeavour Fund Research Programme using natural analogues to assess mCDR.”

Declared interests

Richard Betts was involved in the writing of the report.

All others have their declaration listed below their quote.