Climate Change Glossary: Definitions of Key Terms
Confused by all of the climate terms out there and not sure what lingo to use? Our climate change glossary is designed to help you sort through all the jargon and demystify some of those technical sounding terms. Search below for definitions of the top terms you need to know when talking about climate change, carbon emissions, and climate action.
Climate Change
Climate Change: Refers to a long-term change in the average weather conditions of a place. Beyond changing temperatures, climate change can also alter precipitation patterns and increase the frequency and intensity of droughts, floods, hurricanes, and other extreme weather events. While some climate change occurs naturally, the current change in the global climate is happening at an unprecedented rate due to rising levels of greenhouse gases.
Global Warming: Though this term is often used interchangeably with “climate change,” global warming refers only to the rise in the Earth’s surface temperature. In other words, global warming is one aspect of climate change.
Emissions and Measurement
Greenhouse Gases (GHGs): Gases such as carbon dioxide, methane, nitrous oxide, and fluorinated gases that act like “greenhouses” by trapping heat in the atmosphere. As such, they play an important role in keeping the planet at a livable temperature. While greenhouse gases are produced naturally, the amount of these gases that blanket the planet has skyrocketed since the Industrial Revolution.
Carbon Footprint: When you add up all of the greenhouse gas emissions (GHGs) that you produce – that’s your carbon footprint. A carbon footprint is usually expressed in metric tons (MT) of carbon dioxide equivalent (CO2e). Tools such as carbon footprint calculators or methodologies such as the GHG Protocol can be used to calculate a company or individual’s carbon footprint.
This article explores some of the activities that contribute to tourism’s carbon footprint.
Carbon Dioxide Equivalent ( CO2e): Along with carbon dioxide, there are other greenhouse gases, such as methane, and nitrous oxide, that also contribute to global warming. When measuring a carbon footprint, it is important to account for all of these GHGs; however, the challenge is that they each have a different effect on the climate. Carbon dioxide equivalent, abbreviated as CO2e, is a common unit for measuring greenhouse gases so they can be reported in a single combined footprint. It represents the amount of carbon dioxide that would have the equivalent global warming impact as another greenhouse gas, when measured over a 100-year timescale. For example, one metric ton of methane would be equal to 25 metric tons of CO2e, because it has a global warming potential 25 times that of CO2.
Metric Ton (MT): Also known as a tonne, a metric ton is a unit of mass equal to 1,000 kilograms or 2204.62 pounds. It is the standard unit used for reporting CO2e emissions. This should not be confused with a US ton, which is a unit of mass equal to 2,000 pounds or approximately 907.19 kilograms.
Scope 1, 2, and 3 Emissions: A carbon footprint can be broken down into three different scopes, or classes of emissions sources, as identified by the GHG Protocol, which provides the world’s most widely used greenhouse gas accounting standards.
- Scope 1 Emissions: Direct emissions from fuel combustion in owned equipment such as furnaces, boilers, vehicles, etc. Scope 1 also includes any fugitive emissions such hydrofluorocarbons (HFCs) released by refrigeration and air conditioning systems.
- Scope 2 Emissions: Indirect emissions from the electricity, steam, heat, or cooling an individual or company purchases from a utility provider.
- Scope 3 Emissions: All other indirect emissions that are associated with an individual or company’s activities. Scope 3 emissions are produced by assets that are not owned by the individual or company. This includes emissions generated across the supply chain from the procurement of goods/services, employee travel and commuting, and waste disposal.
Carbon Sink: a natural or artificial reservoir which absorbs and stores more carbon from the atmosphere than it releases. Examples of natural carbon sinks include trees, mangroves and other plants, as well as soils and oceans; whereas artificial carbon sinks include man-made sinks such as carbon capture and storage technologies.
Climate Targets and Action
Science-Based Targets: Emissions reduction targets that are in line with what the latest climate science deems necessary to meet the Paris Agreement goal of limiting global warming to 1.5°C above pre-industrial levels.
Climate Mitigation: Taking action to address the root causes of climate change by preventing or reducing the release of greenhouse gas emissions into the atmosphere.
Climate Adaptation: Taking action to adjust to the changing climate in order to minimize harm from the inevitable impacts of climate change, such as rising sea levels, drought, tropical storms, etc. Examples of climate adaptation strategies include restoring coastal buffer zones, planting climate-resilient crops, reusing greywater, and fortifying buildings and infrastructure.
Carbon Neutral:
Carbon Neutral: A state in which greenhouse gas emissions are reduced as much as currently possible and balanced by an equivalent amount removed or offset, resulting in no net addition to atmospheric CO2. (UNFCCC)
Our recommendation: “Carbon neutral” has become increasingly confusing to consumers, with differing opinions about the role carbon offsets should play in supporting the claim. We recommend moving away from the term and instead communicating that you are working toward net zero as a future goal. See Net Zero below for guidance on setting and communicating a credible target.
Regulatory note (EU): From 27 September 2026, the EU’s Empowering Consumers Directive (EmpCo, Directive (EU) 2024/825) prohibits marketing a product as “carbon neutral,” “climate neutral,” or similar to EU consumers if the claim is based on offsetting emissions outside the product’s value chain.
Net Zero: A company reaches net zero when it has cut its greenhouse gas emissions as much as possible — typically by 90% or more — across all three scopes and removes whatever small amount remains by permanently capturing it from the atmosphere (for example, through reforestation or carbon capture technology). The goal is that emissions and removals balance out, leaving no net addition to the atmosphere.
In practice, “net zero” is most commonly used as a forward-looking commitment that businesses state they are working towards.
Companies are increasingly expected to start building up the removals well before their net-zero target date, rather than leaving it all to the last minute. New guidance from the Science Based Targets initiative (SBTi), expected to take effect from 2028, will require companies to begin phasing in removals from 2035 onward.
Regulatory note (EU): From September 2026, EU rules (the Empowering Consumers Directive) mean a company can only claim “net zero by [year]” if it is backed by a publicly available plan showing how it will actually get there. Progress must also be regularly verified by a third-party expert. A vague promise isn’t enough.
Absolute Zero / Zero Emissions: A stricter standard than net zero. Absolute zero means an organization produces no greenhouse gas emissions at all, not even a small residual amount to offset or remove. There’s no reliance on carbon capture, offsets, or removals; every source of emissions has been eliminated entirely.
In practice, this is extremely difficult to achieve for most businesses. Some sectors, like aviation or heavy industry, may never realistically reach it. This is why “net zero” — cutting emissions as much as possible and dealing with the small remainder through removals — is the more common and achievable target.
Regulatory note: Because absolute zero doesn’t involve any offsetting, it isn’t directly affected by EmpCo’s restrictions on offset-based claims. However, if a company claims “zero emissions” or “absolute zero” without it being literally true (i.e., they still have some emissions, even if small), this would fall under EmpCo’s general ban on unsubstantiated or misleading environmental claims.
Climate Positive: A state where an organization goes beyond balancing its emissions by removing more carbon from the atmosphere than it emits, creating a net benefit for the climate rather than just a neutral impact. This goes a step further than net zero.
A word of caution: unlike “net zero,” there’s no single agreed definition or standard behind “climate positive.” Different organizations use it in different ways, and it’s sometimes used interchangeably with “carbon negative” or, confusingly, “carbon positive” — a term which means the opposite: emitting more carbon than is removed. Because of this inconsistency, we recommend avoiding using “climate positive” or “carbon positive” unless you clearly explain alongside the claim what you mean, what’s being measured, and how the claim is calculated.
Regulatory note (EU): Like “carbon neutral,” under the EmpCo Directive, “climate positive” cannot be used for a product based on offsetting emissions outside the value chain, and any such claim must be backed by verifiable evidence.
Carbon Offsets
Beyond Value Chain Mitigation (BVCM): Actions companies take to reduce or remove greenhouse gas emissions outside their own operations and value chain. This often includes funding verified carbon offset projects. It helps accelerate global climate action but does not replace reducing emissions within a company’s own operations and value chain.
Carbon Offsets (Climate Contributions): Carbon offsets are a way for individuals and businesses to collectively fund climate projects around the world that avoid new greenhouse gas emissions or remove existing greenhouse gases from the atmosphere. They allow you to support climate solutions at a larger scale and do more to address climate change than you could through your own travels or business operations alone. To qualify as carbon offsets, both the projects and the emissions reductions or removals they generate must be independently verified under a recognized standard.
There are different types of carbon offset projects located around the world. Their activities may include building wind farms, protecting forests, restoring mangroves, installing waste-to-energy systems, or sequestering carbon in soil. These projects often create benefits that go beyond emissions reductions, supporting local communities and safeguarding natural biodiversity.
The term climate contributions is increasingly used instead of carbon offsets to emphasize that these investments support climate action beyond your own footprint, rather than canceling it out.
More details on how carbon offsets work.
Carbon Credit: When you buy carbon offsets, you are essentially purchasing a certain number of carbon credits. Each carbon credit represents 1 metric ton of CO2e removed or averted from the atmosphere. So to fund a reduction equivalent to 10 metric tons, you would need to purchase 10 carbon credits.
Each carbon offset project issues a certain number of carbon credits that corresponds to the total amount of carbon emissions that will be reduced during its lifespan. When you purchase carbon credits, the funds are distributed to the project, making the continuation of its activities economically feasible.
Carbon credits are a tradable commodity. When an individual or a business purchases a carbon credit, it must be permanently retired from the market to ensure that someone else can’t also buy it. When you invest in climate action with Sustainable Travel International, we take care of purchasing the carbon credits for you and making sure they are consequently retired.
While many companies purchase carbon credits voluntarily (this is known as the voluntary carbon market), some companies are legally required to purchase carbon credits in order to meet international and national regulatory targets (this is known as the compliance carbon market).
Carbon Offset Project Developer: The individual or organization who oversees the coordination and implementation of a carbon offset project.
Carbon Credit Standards: A standard is a set of criteria against which carbon offset projects’ environmental and social co-benefits can be certified or verified. In the voluntary markets, a number of competing standard organizations have emerged with the intent of increasing credibility in the marketplace.
You can learn more about the different carbon credit standards on our quality assurance page.
Carbon Credit Registries: A registry is a database that issues carbon credits for verified projects and tracks the ownership, sale, and retirement of these credits. Each carbon credit is given a unique serial number to track its ownership throughout its lifetime. A carbon credit can change ownership multiple times; however, if the buyer wants to claim the credit, then it must be permanently retired on the registry so it can’t be resold. As such, registries are important to minimize the risk of double-counting.
