Latest science on the 1.5°C limit of the Paris Agreement

The 1.5°C limit is the enduring, legally significant temperature goal of the Paris Agreement, and along the requirement to achieve net zero greenhouse gas emissions in the second half of the century, sets the legal framework for understanding the level of ambition Parties have committed to under the Paris Agreement.  This limit is often seen as key to the survival of the most vulnerable countries and is grounded in robust scientific evidence.

The 1.5°C limit and net zero goals of the Paris Agreement  are designed to be operationalised to provide guidance – based on the best available science – to show emission reduction rates needed to avoid and/or limit overshoot, and as well the required rollout rate for renewable energy, electric vehicles, energy efficiency, methane reductions and many other aspects of energy and climate policy.

Established to avoid the most dangerous impacts of climate change, particularly for the most vulnerable countries, the 1.5°C threshold represents an ethical and moral boundary. Since its adoption in 2015, the science underpinning the necessity of this limit has only grown more conclusive. Exceeding it would significantly increase the likelihood of severe, widespread, and irreversible, impacts.

 In 2024, global annual average temperature exceeded 1.5°C above pre-industrial levels, marking the warmest year on record. This record temperature reflects a combination of increasing anthropogenic greenhouse gas emissions, reduced air pollution, and short-term natural variability including El Niño. It’s important to note that the Paris Agreement 1.5°C limit refers to long-term human-induced warming assessed over 20- to 30-year periods above pre-industrial time. By that definition, this limit has not yet been reached.

However, current trends show that we are rapidly nearing this limit. Already, climate impacts are intensifying across regions and sectors, with disproportionate effects on vulnerable populations. These include extreme heat, droughts, floods, and biodiversity loss – many of which are now being observed at higher frequency and severity.

Every increment of warming increases the probability and intensity of climate-related hazards. Exceeding 1.5°C will substantially and adversely affect food security, water availability, public health, and infrastructure – especially in regions with limited adaptive capacity. Global warming beyond 1.5°C will significantly increase the risk of ecosystem collapse and accelerate biodiversity loss, increasing species extinction and the disruption of critical ecological functions that support life on Earth.

Without substantial reductions in global emissions by 2030, sustained and high overshoot of the 1.5°C limit will become inevitable. Overshoot is defined as temporarily exceeding the 1.5°C limit before returning below level as quickly as possible.

If emissions are reduced quickly enough, then overshoot can be limited and  the dangers of carbon cycle and other earth system feedbacks that could amplify warming strictly limited.

The science is clear: rescuing 1.5°C means taking urgent actions that limit the likelihood, magnitude, and duration of overshoot. Immediate and sustained reduction in emission across all sectors, rapid phase-out of fossil fuels, global net-zero CO₂ around 2050—followed by net-zero GHGs by the 2070s with net negative emissions thereafter.  Achieving net zero by the 2070s is critical to reducing warming significantly below 1.5oC by 2100 - the extent of net negative CO2 emissions will determine how far warming drops by 2100.

Achieving net negative CO2 emissions through the scaled deployment of carbon dioxide removal is essential to bring temperatures down from peak levels to well below 1.5°C by 2100, thereby reducing long-term risks such as ice sheet tipping points, ocean acidification, and deoxygenation, and giving coral reefs a chance of recovery. Maintaining +1.5°C global warming would lead to long-term multi-metre sea level rise as well as the risk of abrupt sea level rise from destabilisation of the Western Antarctic ice sheet and parts of the East Antarctic ice sheet.

While early and decisive action can significantly reduce future damages, it cannot eliminate them entirely. If warming exceeds 1.5°C, we increase the likelihood of crossing critical tipping points. The coming years will determine whether we can avoid the most damaging impacts of climate change or face a future marked by the escalating risk of irreversible ice loss, shifts in ocean circulation, and collapse of ecosystems.

In emission terms what is needed includes deep GHG reductions for 2030 and 2035 NDCs and Global net-zero CO2 by ~2050 to halt warming and strictly limit any overshoot. We will need to focus on the fastest possible phase out of fossil fuels, and plan for rapid technological carbon dioxide removal for decades after deep GHG reductions. Achieving net zero GHGs by the 2070s would ensure warming drops from peak levels, reducing risks in ice sheet tipping points, ocean acidification and deoxygenation, to give coral reefs a chance at recovery.

The solutions are clear. It is established that it is technologically and economically feasible to make the rapid changes needed, and the main barriers to this are political.

This document provides a comprehensive overview of what the science is saying now about 1.5°C – what it means, what is at stake, and what actions are needed to limit the risks of overshoot and safeguard a liveable future