The National Emergency Briefing on climate November 2025

Background

Many of us have heated a saucepan of milk on a hob at its lowest setting to warm it slowly to body temperature (37°C) for our baby or child. We know that turning a hob to “9” or “High” will warm it quicker, but even on a gas hob we also know that, even if the gas is turned off before the milk reaches 37°C, it is very difficult to prevent it from overheating. With an electric hob or a heavy metal-lidded pan, it is virtually impossible to judge accurately. Consequently, the milk may start to boil or even boil over, because simply turning the dial to zero does not stop stored excess heat energy in the hob and pan from continuing to transfer to the milk for several minutes and before it will start to cool back to the intended temperature.

The Earth is similar, but the consequences are already far more serious than spilt milk and far more complicated with multiple processes, some interdependent, that either reduce or increase the rate of warming and that operate on instantaneous to geological timescales. Some may switch, or tip, from negative forcing effects that had maintained the past equilibrium to positive effects that accelerate divergence away from it. 

Climate stability only occurs when the incoming solar power (at a global 24hr average of 340W/m², mostly arriving as visible light) is balanced by energy radiated back into space, mainly as heat and infra-red light. Atmospheric aerosols (clouds) and ice reflect some incoming solar energy, while greenhouse gases (GHGs) such as CO₂, methane and water vapor trap infra-red, heat energy (Cloudy nights are warmer than clear ones.).

Anthropogenic emissions are small (2-3%) relative to natural fluxes, but they are the entire source of the net atmospheric increase, as natural emissions are normally balanced by natural sinks. Anthropogenic GHGs come from burning fossil fuels (70%), agriculture (20%), land-use change (6%) and industrial and waste processes (4%).

Prior to 1850, the Earth experienced around 10,000 years of climate stability. All GHG emissions from respiration, decay and volcanism were balanced by sequestration through chemical weathering, photosynthesis and ocean uptake, a natural “Net Zero”, or Goldilocks state, that was “just right” for humans, our crops, livestock and evolved global ecosystems.

Since the 19th century, anthropogenic CO₂ has accumulated in the atmosphere, rising from 280 parts per million (ppm) to 426 ppm by December 2025. Other greenhouse gases increase this warming effect, to an equivalent of around 542–545 ppm CO₂-equivalent. In recent decades cloud cover (including pollution-derived aerosols) and ice cover have both declined, reducing their net cooling or negative forcing effect.

The result is that Earth now retains approximately 2.5–3 W/m² more energy than in pre-industrial times. To put this in context, raising the temperature of 1 millilitre of water by 2°C in one second requires about 8 watts of power—seemingly trivial. However, spread across the Earth’s surface area of 5.1 × 10¹⁴ m², this excess represents an additional ~10¹⁵ watts of continuous heating. Over 24 hours, that is equivalent to the energy released by over one million Hiroshima-scale nuclear explosions every day.

Most of this excess heat is absorbed by the oceans, contributing significantly to observed sea-level rise through thermal expansion and ice melt, while the remainder has raised global mean surface temperature by approximately 1.5°C above pre-industrial levels. This is widely regarded as the upper safe limit for our post-glacial ecosystem. Exceeding it is akin to feeding a baby hot milk…so not good.

Had global emissions as was agreed, begun falling from 2015, we might have avoided this outcome. Instead, anthropogenic emissions have continued to rise, reaching approximately 54 billion tonnes CO₂-equivalent in 2024, increasing atmospheric CO₂ by a record 3.7 ppm that year.

Like the pan left on a hot hob, even turning emissions to zero today will not stop further warming. As explained by Hansen et al in their “Global Warming in the Pipeline” paper, global temperature lags behind changes in greenhouse gas concentrations and cloud/ice feedbacks, with around 40% of warming occurring within a decade and around 60% unfolds over a century or more, unless greenhouse gases are actively removed through residual natural sequestration processes, as-yet undeveloped Carbon Capture and Storage technologies and solar radiation management that are collectively capable of reducing incoming solar power by at least 3–4 W/m² to limit future warming but by substantially more to halt let alone reverse the current warming trend.

The Earth’s atmosphere is already 1.5°C warmer. Without urgent action, it will reach 2°C in the 2030s. It may reach 3°C by 2050, at which point a rise to 4°C by 2100 becomes probable as one or more tipping points are passed for global processes and their feedbacks switch from reducing to increasing warming, even if or after “Net Zero” is eventually achieved. e.g. On loss of sea and land surface ice cover, that had reduced incoming solar power by reflecting it away into space energy, it is replaced by dark surfaces that retain it as heat so further increasing the global energy imbalance.  The accumulated excess greenhouse gases in the atmosphere and oceans will persist for centuries, keeping the planet in energy imbalance unless net-negative emissions are achieved at comparable scales to current rates of their emission.

The National Emergency Briefing

On 27 November 2025, a National Emergency Briefing addressed nine critical aspects of the unfolding consequences of our collective failure to prevent, and now reverse, the Earth’s energy imbalance by taking a holistic, wide ranging but UK centric approach.

Presentations were delivered to Parliamentarians by leading experts in their respective fields:

1. Nature – Professor Nathalie Seddon, Founding Director, Nature-based Solutions Initiative & The Agile Initiative, University of Oxford

2. Climate – Professor Kevin Anderson, Professor of Energy and Climate Change, Universities of Manchester, Uppsala and Bergen

3. Tipping Points – Professor Tim Lenton, Founding Director, Global Systems Institute, University of Exeter

4. Weather Extremes – Professor Hayley Fowler, Founding Director, Nature-based Solutions Initiative & The Agile Initiative, University of Oxford

5. Food Security – Professor Paul Behrens, British Academy Global Professor and expert in food system transformation

6. Health – Professor Hugh Montgomery, Director, Centre for Human Health, University College London

7. National Security – Lieutenant General Richard Nugee CB CVO CBE (Retired)

8. Economics – Angela Francis, policy expert in green economics

9. Energy Transition – Tessa Khan, energy transition expert

The presentations may be viewed at:  https://www.nebriefing.org/  . and a film will be released in early 2026. 

While their conclusions outline unvarnished and potentially catastrophic consequences, they also detail remaining opportunities for meaningful individual and collective action at national or international levels that would mitigate and limit the severity of our transition to a significantly hotter world than our civilisation has developed under.  This will persist for centuries and result in substantial sea level rise of at best one-meter, significant areas that will cease to be habitable or support food production, resulting in mass migration and adaption to residual available food supplies. Global Solar radiation management in the absence of action may prove to be the only effective, feasible and timely method of last resort. 

At worst the long-term impacts of not restoring the Earth’s energy imbalance will include the transition of existing tropical rain forest to savanna, increased rate of and potentially complete loss of terrestrial ice sheets with possibility of ice free poles, the melt waters stalling oceanic thermohaline currents responsible for heat transfer from equatorial to higher latitudes, halting both oxygen transfer to the ocean depths and reciprocal nutrient upwelling in addition to the immediate impacts of flooding followed by droughts to the world’s cereal growing regions and a cascade of other impacts, none pleasant.  All of these will take place over the next centuries if unchecked and culminate in the Earth more closely resembling the Eocene, 50 million years ago. However, the Eocene’s Thermal Maximum developed over millions of years as a result of GHG release from sustained regional volcanism whereas our emission of equivalent quantities has been achieved in under 200 years, a thousand times faster, and so denies the time required for evolutionary adaption by most existing species triggering extinction rates not experienced since the end of the Jurassic or Permian eras,