Key climate terms

This glossary provides plain-English definitions of the key terms behind the City of London's work on net zero, climate resilience, and sustainable growth. Terms are listed alphabetically for ease of reference, followed by a dedicated section explaining how emissions are measured and categorised.

Adaptation refers to actions that help reduce vulnerability to the current or expected impacts of climate change like weather extremes and hazards, sea-level rise, biodiversity loss, or food and water insecurity.

Air pollution is the presence of substances in the air that are harmful to humans, other living beings, or the environment. Pollutants can be gases, like ozone or nitrogen oxides, or small particles like soot and dust. Both outdoor and indoor air can be polluted.

Air quality refers to the measure of how clean or polluted the air is, which includes the presence of solid particles and gaseous pollutants. Good air quality means the air is clear with minimal pollutants, while poor air quality contains high levels of harmful substances that can affect health and the environment.

Biodiversity refers to the variety of life on Earth or in a particular place - from the diversity of environments where plants and animals live, to the range of species found within them, and the genetic variation within each species. It underpins healthy, resilient natural systems and provides essential benefits, from clean air and water, to food, materials and wellbeing.

BREEAM (Building Research Establishment Environmental Assessment Method) is a sustainability assessment method for planning projects, infrastructure and buildings. It assesses an asset’s environmental, social and economic sustainability performance.

Capital goods are physical, human-made assets (things like buildings, machinery and equipment) that organisations use to produce goods or deliver services. Unlike raw materials or energy, they are not used up in the process; instead, they are the long-lasting tools that keep businesses and economies running and growing.

Carbon footprint is a measure of the amount of greenhouses gasses released into the atmosphere as a result of the activities of a particular individual, organisation, or community. All gases are converted into a single comparable figure, carbon dioxide equivalent, to give an overall picture of impact.

Carbon removal / sequestration is the deliberate process of taking greenhouse gasses out of the atmosphere and storing them securely often through natural means, such as planting trees, to reduce the concentration in the atmosphere and help limit climate change.

Circular economy refers to an economic system that is designed from the outset to keep resources in use for as long as possible - through reuse, repair and remanufacturing - rather than disposing of them. It moves away from the traditional "make, use, throw away" approach by building longevity and recovery into products and materials from the start.

Climate action refers to the steps taken by individuals, organisations, communities and governments to reduce greenhouse gas emissions and adapt to the effects of a changing climate. It encompasses everything from policy and investment decisions to everyday behaviours and built environment changes.

Climate change refers to long-term shifts in global temperatures and weather patterns driven primarily by human activity. The burning of fossil fuels, deforestation and industrial processes release greenhouse gases that trap heat in the atmosphere, leading to rising temperatures, more extreme weather events, rising sea levels and disruption to natural systems across the planet.

Climate resilience is the capacity of ecosystems, societies, and organisations to anticipate, prepare for and respond to climate risks and hazards such as extreme heat or flooding. A climate-resilient society effectively copes with and manages the impacts of climate change while preventing those impacts from worsening.

Decarbonisation is the process of reducing and ultimately eliminating the greenhouse gas emissions, particularly carbon dioxide (CO2) that drive climate change. This means transitioning away from fossil fuels and other high-emission activities across energy, transport, industry and construction, towards cleaner alternatives that release little or no carbon into the atmosphere.

Ecosystem services are the many benefits that nature provides to people. These services support human wellbeing by providing essentials such as food and water, support mental and physical wellbeing, and perform vital functions like regulating the climate, filtering pollutants and reducing the impact of extreme weather events.

Embodied carbon refers to all the greenhouse gas (GHG) emissions produced across the entire life cycle of a product or material, including raw material extraction, transport, manufacturing, construction, maintenance, and end-of-life. It captures all GHGs released throughout the supply chain.

EPC (Energy Performance Certificate) is an official document that rates how energy-efficient a property is, on a scale from A (most efficient) to G (least efficient). It also provides estimated energy costs and highlights key features affecting the property's energy performance, such as insulation and heating systems.

Green corridors are planned networks of natural vegetation designed to act as pathways or links in the landscape. They connect isolated green spaces like parks, forests, and wetlands into a cohesive system. By connecting these spaces, they allow wildlife to move freely through both urban and rural landscapes, supporting biodiversity and the health of natural environments.

Green economy is an economic system that seeks to grow and create prosperity without depleting natural resources or damaging the environment. Instead of depleting natural resources or polluting the environment to drive growth, it focuses on clean energy, sustainable industries and smarter use of resources - creating jobs and prosperity in ways that protect the planet for the long term.

Green infrastructure is a planned network of natural and semi-natural spaces - such as trees, parks, green roofs, and green walls – that work together to make urban areas more sustainable. These features help manage rainwater, reduce heat, improve air quality, and create healthier, more resilient cities.

Greenhouse gases (GHGs) are the emissions responsible for global warming. These include methane, nitrous oxide, carbon dioxide, and fluorinated gases amongst others.

Gross emissions refer to the total amount of greenhouse gases emitted into the atmosphere over a specific period.

Just transition is the fair and inclusive shift towards a low-carbon economy, one that safeguards human rights, promotes sustainable development, reduces poverty, and supports the creation of decent work. It aims to ensure that the wide-ranging benefits of a green economy are equally shared, while also addressing the social and economic challenges faced by those most at risk of losing out whether they be countries, industries, communities, workers, or consumers.

ktCO₂ is the unit of measurement for GHG emissions. It standardises greenhouse gases into units of kilotonnes of carbon dioxide equivalent (ktCO₂e)

Low-carbon economy is one structured around energy sources and industries that produce little or no greenhouse gas emissions. This means moving away from fossil fuels like coal, oil and gas, towards renewable alternatives such as solar, wind and hydroelectric power. It supports economic growth and social progress while promoting energy efficiency across industries, transport, and buildings.

Mitigation involves actions that addresses the root causes of man-made climate change – primarily by reducing greenhouse gas emissions or removing them from the atmosphere. This includes decreasing emissions from energy production and consumption, by improving energy efficiency or transitioning from fossil fuels to renewable energy, changes in land use, and enhancing carbon sinks, for example, by restoring forests. These measures are designed to slow, and ultimately halt, the rise in global average temperatures driving changes in Earth’s climate.

Net emissions refer to the balance between the total amount of greenhouse gases (GHGs) released into the atmosphere and the amount removed.

Net zero is achieved when human-caused greenhouse gas emissions are balanced by human efforts to remove the same quantity of emissions from the atmosphere over a specified period (Science Based Targets initiative (SBTi)). N.B. Further guidance on the definition of net zero and its guiding principles are due later in 2026 from the SBTi.

Offsets is a mechanism that allows individuals, businesses, and organisations to compensate for their greenhouse gas emissions by funding projects that reduce or remove emissions elsewhere.

Retrofit is the process of upgrading existing buildings with new or modified features and technology to improve their sustainability, including energy efficiency and climate resilience.

Science-based / Paris-aligned GHG emissions reduction targets are considered “science-based” if they are in line with what the latest climate science says is necessary to meet the goals of the Paris Agreement (2015) - to limit global warming to well below 2°C above pre-industrial levels and pursue efforts to limit warming to 1.5°C.

Scopes of emissions categorise greenhouse gas emissions by their source and the level of ownership an entity has over them. They are grouped into three categories. More information on what this means for an organisation and city is at the bottom of the page.

SuDS  (Sustainable Drainage Systems) are a range of sustainable measures for surface water management which reduce the amount, flow or rate of surface water discharge into sewers.

Sustainable finance refers to the process of integrating environmental, social and governance (ESG) considerations into investment decisions in the financial sector, leading to more long-term investments in sustainable economic activities and projects.

Urban greening is a process of adding green infrastructure in an urban area. Due to the morphology and density of the built environment in The City, green roofs, green or living walls, street trees, and techniques such as soft landscaping, are the most appropriate elements of green infrastructure.

Urban Greening Factor refers to a model to assist boroughs and developers in determining the appropriate provision of urban greening for new developments.

Urban Heat Island Effect sees dense urban areas experiencing hotter temperatures due to the absorption and slow release of heat from buildings.

Whole life carbon refers to the total carbon emissions associated with a product, structure, or building over its entire lifespan. This includes emissions from raw material extraction, manufacturing, transportation, use, maintenance, and eventual disposal.