Why the vocabulary matters
News about energy and climate leans on a compact set of technical words. Some are used loosely, some mean slightly different things depending on who is speaking, and a few are easy to mix up. This glossary gives short, neutral definitions of the terms beginners meet most often. It is general information, not advice, and it does not speak for any company or organization.
Definitions are grouped by theme. Where a term has its own detailed explanation elsewhere on this site, the entry here stays brief.
Climate basics
Greenhouse gases. Gases in the atmosphere that trap heat. Carbon dioxide, methane and nitrous oxide are the best known. Human activities, including burning fossil fuels, farming and land clearing, add to their concentrations.
Emissions. The release of greenhouse gases into the atmosphere. Totals are usually given in tons of “carbon dioxide equivalent,” a way of expressing different gases on a common scale.
Global warming and climate change. Global warming refers to the long-term rise in average surface temperatures. Climate change is broader and includes shifts in rainfall, sea level and the frequency of some extreme weather. Scientists describe these changes with ranges and confidence levels, and estimates vary between studies.
Mitigation and adaptation. Mitigation means reducing emissions or removing greenhouse gases from the air. Adaptation means adjusting to the effects already happening or expected, for example by building flood defenses.
Carbon sink. Anything that absorbs more carbon than it releases, such as forests, soils and oceans.
Counting emissions
Carbon footprint. An estimate of the greenhouse gases linked to a person, product or organization. Different methods draw the boundary in different places, so figures are not always comparable.
Scope 1, 2 and 3. Categories used in corporate reporting. Scope 1 covers direct emissions, Scope 2 covers emissions from purchased electricity or heat, and Scope 3 covers everything else along the value chain, which is often the largest and hardest part to measure.
Life cycle assessment. A method that tallies impacts from raw materials through use and disposal. Results depend on assumptions, so two studies of the same product can differ.
Carbon offset. A credit meant to represent a reduction or removal of emissions elsewhere, which a buyer uses to compensate for their own. Quality and permanence are debated.
Targets and policy
Net zero. A state in which emissions put into the atmosphere are balanced by emissions removed. It does not mean zero emissions. Many governments and organizations have announced net zero targets, and the dates, scope and methods differ widely.
Decarbonization. The process of reducing the carbon intensity of an activity, such as power generation, transport or heating.
Energy transition. The gradual shift from one mix of energy sources to another, currently often described as a move away from fossil fuels. It unfolds at different speeds in different places.
Carbon pricing. A policy that puts a price on emissions, either through a tax or through a trading system with a cap on total emissions. Supporters and critics disagree about the right level and design.
Climate agreements. International arrangements in which countries set goals for limiting emissions. Commitments are generally set by each country and compliance relies largely on political pressure.
Energy sources and technology
Fossil fuels. Coal, oil and natural gas, formed from ancient organic matter. Burning them releases carbon dioxide.
Renewable energy. Energy from sources that are replenished naturally on a human timescale, such as sunlight, wind, flowing water and heat from the earth. Renewable does not automatically mean free of environmental impact.
Energy mix. The combination of sources a country, region or company uses to meet its energy needs.
Primary and final energy. Primary energy is the raw energy in fuels and natural flows. Final energy is what reaches the consumer, for example electricity at a socket. Some energy is lost in conversion, which is why the two numbers differ.
Carbon capture. Technology that separates carbon dioxide from industrial exhaust or from the air so it can be stored or used. Costs, energy needs and long-term storage are active areas of study.
Hydrogen fuel. Hydrogen used as a fuel or industrial input. Its climate impact depends on how it is made, and “green,” “blue” and “gray” are informal labels for different production routes.
Energy storage. Ways of holding energy for later, from batteries to pumped water. Storage helps balance supply and demand when output from sources like wind and solar varies.
Power system terms
Electricity grid. The connected network of power plants, high-voltage lines, substations and local wires that delivers electricity.
Capacity and capacity factor. Capacity is the maximum output a plant can produce. Capacity factor compares what it actually produced over time with that maximum, which is why a wind farm and a gas plant of equal capacity can deliver different amounts of energy.
Baseload and peak demand. Baseload is the minimum level of demand present most of the time. Peak demand is the highest level, often in the evening or during extreme weather.
Grid resilience. The ability of the power system to withstand disruptions and recover quickly.
Energy efficiency. Getting the same service, such as light or warmth, with less energy.
Social and security terms
Energy security. Having reliable and affordable access to energy, a goal with trade-offs between cost, supply diversity and emissions.
Energy access. Whether households can obtain reliable, affordable modern energy for lighting, cooking and heating. Large numbers of people still lack reliable electricity or clean cooking fuels, though estimates are revised and vary by source.
Just transition. The idea that moving away from carbon-intensive industries should consider the workers and communities affected.
Units you will see
Watt and kilowatt-hour. A watt is a rate of power. A kilowatt-hour is an amount of energy: one kilowatt used for one hour. A household bill is usually measured in kilowatt-hours. Mixing up the two is one of the most common mistakes in reading energy figures.
Ton. Emissions are often reported in metric tons, which is slightly more than a US short ton. Check which is meant.
How to use this glossary
Treat definitions as starting points. Words such as “clean,” “green” and “sustainable” have no single agreed meaning, and the same figure can be presented differently depending on what is included. When a report matters to you, look for what it counts, what it leaves out, and what assumptions sit behind its numbers.