Background

The Earth's climate responds to many factors, including temperature. It is changing at speeds that are unprecedented in the past thousands of years. It is occurring as a result of human emissions of greenhouse gases, deforestation, and reductions in the Earth's heat reflectivity (e.g. through loss of ice cover) which lead to global warming. Greenhouse gas emissions are the main source of global warming, and subsequently, of climate change.

Climate change is one of the most significant sources of environmental risks. Climate risks include:

• increased intensity and frequency of extreme weather events.

• these risks lead to loss of ice sheets, glaciers, freshwater, forest cover, biodiversity - also leading to ocean acidification, reduced ocean currents, and extreme heat in some regions

• in turn, these changes threaten food security and physical health and safety globally due to: hydric stress, droughts, extreme heatwaves, high wet bulb temperatures, ecosystem damage, altered precipitations, cyclones

• all of the above translates to increased mortality from heat, food and water scarcity, disease, and armed conflicts, as well as economic disruption through inflation, supply chain disruptions, infrastructure damage and worker health disruptions.

To mitigate these risks, 197 countries have endorsed the Paris Agreement which sets a target limiting net global warming to 1.5°C above pre-industrial levels. 1.5°C is an essential target because after 1.5°C, tipping points and cascading effects become increasingly severe and uncertain: the severity of risks is non-linear and every fraction of a degree counts. This has led some climate and risk experts to consider a risk of 50% GDP contraction and 4 billion casualties between now and 2090. Using lower risk analyses, 1.5°C still marks the boundary between low-risks on one hand, and non-linear, uncertain and extreme climate risks on the other hand.

Briefing - communicating about global targets

1.5°C is a legal and moral obligation that must be protected at all costs 

• The recent International Court of Justice Advisory Opinion confirms 1.5°C by the end of the century as the agreed primary temperature goal under the Paris Agreement. 1.5°C is a line in the sand for unacceptable impacts, an “ethical and moral boundary” crucial to the survival of the most vulnerable. 

• Every fraction of warming matters: each tenth of a degree avoided saves lives, livelihoods, ecosystems and money. The choices we make now will define our future.

Reframing the debate: 1.5°C as a guardrail not a cliff

• 1.5°C remains our target, and we must limit the size and duration of any overshoot. Communications must avoid binary fatalism (“1.5°C is dead”) and instead emphasise agency: “how quickly can we course correct?”.

  
  

• Talking about 1.5°C using a safety and health frame resonates better with publics and leaders: every increment of warming makes our societies more unsafe, unfair, and uncertain.

Progress is real—but too slow

• Thanks to Paris Agreement commitments helping to actively bend the curve down, warming pathways have fallen from ~4°C of projected warming by 2100 to around 3°C. The vast majority of countries have prepared  climate plans that contribute to closing the emissions and adaptation gaps. Full implementation of these plans, including net zero, LTS, and NDCs targets – a best case scenario –  would reduce that to ~1.9°C of warming.

  
  

• Renewables now generate more than one-third of global electricity. They are “cheaper than new fossils in 90% of the world and the cheapest source of bulk electricity generation”. But adding this additional capacity to the grid is not enough—we must also commit to stop fossil fuel use (and displace existing fossil fuel infrastructure).

  
  

• Yet emissions are still rising. If they are not reduced rapidly, we are likely to temporarily exceed 1.5°C before 2030. This reinforces the case for urgent action, and the need for new, credible NDCs, with near-term, measurable, sectoral targets for renewables, energy efficiency, EVs, and deforestation, which will show concretely how we will close the outstanding 29.4Gt CO2eq gap to stay within the 1.5°C limit.

Overshoot is not a plan

• It is not possible to overdramatise the risks of overshoot. Many of these risks are irreversible—regardless of further efforts—and beyond the limits of what we can adapt to. They could occur at 2°C of warming or less, including particularly the triggering of dangerous tipping points such as ice sheet collapse, coral reef die off, and the slowdown of Atlantic Ocean currents. Everything must be done to avoid these, as well as the serious risks of irreversible ecosystem damage, deadly heat and drought (affecting upwards of 2.3 billion people annually), and increased strain on food systems—including disruptions to agricultural productivity and supply chains.

  
  

• Temporary breaches of 1.5°C do not undo the Paris Agreement goal, which is defined over long-term average temperatures, but they do strongly challenge it. We will need to consider net negative emissions to correct any overshoot and bring temperatures back down by 2100. Scaled deployment of carbon dioxide removal (CDR) can help, but it cannot substitute for fast fossil fuel phase-out. Scientists estimate that CDR can only absorb around 0.2°C of warming, and even that will represent a huge implementation challenge. Nor does it tackle the underlying cause of climate change.

  
  

• The most effective and cheapest way to minimise overshoot is rapid emissions cuts now—and the less we will need to deploy CDR and other expensive and untested technologies in the future.

  
  

There is much to be done this decade

• The science is clear on what is needed: peak global emissions before 2025 to avoid overshoot; cut CO₂ 48% by 2030 (vs 2019 levels) and reach net zero by the 2050s; reduce methane by 45% by 2050 (IPCC WG3 SPM).

  
  

• Countries can do their part by following up on the COP28 commitments to transition away from fossil fuels, triple renewables and double efficiency by 2030, halt and reverse deforestation by 2030, and electrify vehicles by 2035 in developed economies.

  
  

• Finance and cooperation will be key both to support delivery of emission reduction objectives  and to close the adaptation and Loss and Damage finance gaps—especially for SIDS and LDCs already facing the loss of their territories to sea-level rise and/or ever growing costs in the face of intensifying climate impacts.

Useful Resources

• Communicating on 1.5 °C: A Toolkit for Climate Scientists – Grantham Institute, Imperial College London

  • A guide designed for scientists to effectively communicate the urgency and nuances of the 1.5 °C limit to wider audiences. Offers messaging frameworks and advice on navigating public debates.

    
    

• Latest Science on the 1.5 °C Limit of the Paris Agreement – Climate Analytics, 2025

  • A briefing that outlines the legal significance of the 1.5 °C goal, the science backing it, and the pathways required to avoid overshoot. Emphasises the need for rapid mitigation and policy alignment.

    
    

• The 1.5 °C Limit and Risks of Overshoot – Climate Analytics, 2024

  • Examines the consequences of a temporary overshoot—what is reversible, what isn’t, and how even small breaches raise risks in vulnerable regions. Highlights adaptation limits and the growing finance gap.

    
    

• 1,5 °C to Stay Alive: Why We Need the 1.5 °C Limit – Germanwatch, 2025

  • A policy brief explaining why the 1.5 °C limit matters—not just scientifically, but in terms of human security, equity, and climate justice. Puts the target in a geopolitical and ethical perspective.

    
    

• The pursuit of 1.5°C endures as a legal and ethical imperative in a changing world – SCIENCE, 2025

  • This scholarly research details why the 1.5 °C threshold under the Paris Agreement remains legally and politically significant, showing that every fraction of a degree matters and that obligations strengthen before, during, and after any breach.

    
    

• Guest Post: Why 2024’s Global Temperatures Were Unprecedented, but not Surprising – Carbon Brief, 2025

  • Guest post on the Indicators of Global Climate Change, which provides a good snapshot of the state of play on physical science / the planet. Produced using the same methodology as the IPCC WG1.

    
    

• Overconfidence in Climate Overshoot – Nature, 2024

  • This academic article examines overshoot pathways and concludes that technical, economic and sustainability considerations limit the possibilities for carbon dioxide removal deployment, and that temperature decline after overshoot is not achievable within the timescales expected today.

    
    

• Over-reliance on land for carbon dioxide removal in net-zero climate pledges – Nature, 2024

  • This study examines the heavy reliance on land for carbon dioxide removal in net-zero pledges - how much land is needed, where, and when. It highlights a gap between governments’ expectations and the realistic role of land in climate mitigation, calling for greater transparency in land use plans.

    
    

• A Prudent Planetary Limit for Geologic Carbon Storage – Nature, 2025

  • This article argues that the storage potential of geological carbon storage is not unlimited. Only stringent near-term gross emissions reductions can lower the risk of breaching this limit before the year 2200.

    
    

• Global Tipping Points Report – Exeter, 2023

  • The report is an authoritative assessment of the risks and opportunities of both negative and positive tipping points in the Earth system and society. An update is due this year.