Professor Gerald Mills presented “London’s Climate Futures: Beyond the Envelope,” in a session hosted by CIBSE Resilient Cities Group. A physical geographer at University College Dublin, Mills specialises in urban climatology, is a former president of the International Association for Urban Climates, works with the World Meteorological Organization, and is a review editor for the forthcoming IPCC Special Report on Cities and Climate Change. The webinar set out to connect global climate science with the practical realities of how cities are planned, built and managed, moving deliberately from the planetary scale down to streets, buildings and neighbourhoods.
Mills began by grounding the discussion in the global picture: rising atmospheric carbon dioxide, the strengthening greenhouse gas effect, and the planet’s growing energy imbalance. He explained how a tiny concentration of CO₂ in the atmosphere exerts an outsized influence on longwave radiation, driving warming that is now clearly visible in global temperature and ocean heat content records.
The Paris Agreement’s 1.5°C goal was framed not as an abstract target but as a threshold beyond which the climate system shifts into conditions societies are not designed for, especially once more intense heatwaves, heavy rainfall, drought and sea level rise are factored in. Against this backdrop, he emphasised that cities, though occupying only a small fraction of the Earth’s surface, are responsible for roughly 70% of global anthropogenic CO₂ emissions and therefore sit at the heart of both the problem and its solutions.
A central theme of the talk was the need to hold two climate stories together: the global climate that is changing because of human activity, and the urban climate that arises from how cities are built, paved, heated, cooled and inhabited. Mills described how urban form – impermeable surfaces, dense construction, rough building geometry, and high energy use – creates distinct local climates that drive urban heat islands, altered hydrology, poor air quality and increased flood risk.
At the same time, cities remain embedded in a background climate defined by latitude, proximity to oceans and topography, which is itself shifting under global warming. The challenge for planners, engineers and designers is to understand how local interventions at building, neighbourhood and city scales aggregate into wider atmospheric impacts, and how global change will in turn reshape the conditions inside cities.
Turning specifically to London, Mills used local climate projections, greenhouse gas inventories and urban form classifications to show how uneven both risk and responsibility are across the capital. Projections for London point clearly towards warmer conditions, more frequent and intense heatwaves, wetter winters, drier summers, and associated water stress and flood risks.
Mapping local climate zones revealed that the most built-up central districts experience the strongest urban heat island effects, while residential energy performance data showed large areas of poorly performing housing stock, with many dwellings far below the EPC standards that cities now aspire to. London’s emissions profile – broadly divided between domestic, commercial/industrial, and transport sectors – underscores the scale of the retrofit and system change needed, from improving building fabric and heating systems at scale to transforming mobility and power supply.
The closing discussion focused on what this means for adaptation, mitigation and the way we think about urban climate action. Mills argued that zero-carbon city goals speak primarily to mitigation – reducing emissions that occur within city boundaries and eventually tackling hard-to-measure emissions that occur outside city boundaries – while the inevitability of further warming means cities must also invest heavily in adaptation and climate resilience. He stressed that popular measures such as urban greening and tree planting play an important role in cooling and comfort but cannot offset more than a tiny fraction of London’s annual emissions, making systemic changes in energy use and urban form unavoidable.
Key take-home messages included the need to view the city as an interconnected system rather than a collection of isolated projects, to better integrate indoor and outdoor climates in models and decisions, and to build a stronger scientific and monitoring infrastructure – including routine urban CO₂ measurements – so that London can not only plan for its climate future but track whether its actions are genuinely making a difference.
You can find the presentation HERE and watch the recording HERE