Base year for the carbon footprint

Introduction

The base year is a fundamental concept in corporate carbon accounting (CCF) and refers to the reference year against which all subsequent emissions calculations and reduction targets for a company are measured. Without a clearly defined base year, it is impossible to track progress in climate management or to transparently demonstrate the effectiveness of measures. The base year plays a key role, particularly in the context of SBTi targets, CSRD disclosure requirements, and investor communication.

Importance in climate management

The choice of a base year is not merely a formal decision; it shapes the entire logic of the climate strategy. A company that carefully selects its base year can:

• reliably measure its emission trends over time,
• establish science-based climate targets (e.g., in accordance with the SBTi) using a robust baseline and
• Ensure comparability for stakeholders, whether for internal management or external reporting.
  

It is particularly crucial for investors, regulatory authorities, and customers that progress be reported relative to a recognized, stable baseline year. Without this benchmark, emissions reductions remain arbitrary and difficult to verify. The GHG Protocol and the Science Based Targets initiative (SBTi) therefore require companies to establish a baseline year when setting ambitious climate targets.

Criteria for selecting the base year

A base year should always be chosen so that it is both reliable and representative. Several criteria are key in this regard:

• Data availability: The base year can serve as a solid starting point only if complete, valid, and verified emissions data are available for it.
• Representativeness: The base year should reflect a “normal” fiscal year. Years with exceptional one-time events—such as a pandemic, mergers, or production shutdowns—skew the comparison and should be avoided.
• Long-term traceability: The selected year should remain consistent over time. Changes to the base year—known as rebaselining—are appropriate only in exceptional cases (e.g., acquisitions or changes in methodology) and should be transparently documented.
  

These criteria ensure that the base year is not merely a statistical figure, but serves as a credible foundation for strategic decision-making in climate management.

Typical use cases

The base year is used in many contexts of climate management. It is most commonly used in corporate carbon footprint (CCF) calculations, where it serves as the starting point for reduction pathways. Companies regularly report on their progress by comparing current emissions to the base year.

Furthermore, the base year is a key tool in stakeholder communication: investors, business partners, and customers expect clear and transparent progress reports that show emission reductions relative to a specified year. It also plays an important role in sustainability management, as internal key performance indicators (KPIs)—such as emissions per revenue or per employee—are often measured relative to the base year.

Relevance for Businesses

The choice of a base year is not merely a methodological decision; it also has a strategic dimension. It plays a decisive role in how ambitious the set targets are perceived to be. A company that chooses a year with exceptionally high emissions as its base year risks being accused of greenwashing, because reductions appear easier to achieve in comparison.

At the same time, the base year is of great importance for internal management: it makes it possible to quantify successes and failures, communicate progress, and consistently align actions with long-term reduction targets. For companies subject to CSRD reporting requirements, the transparent presentation of the base year is a crucial part of the mandatory disclosures.

Relationship to Standards and Regulations

Several international standards and legal frameworks explicitly address the significance of the base year:

• The GHG Protocol requires that a base year be clearly defined and documented.
• The Science Based Targets initiative (SBTi) requires the use of a base year that enables the setting of science-based and verifiable targets.
• Under ESRS E1 of the CSRD, transparency regarding methods and base years is required.
• ISO 14064 also sets out clear guidelines for selecting and adjusting base years.
  

Practical Tips for Navigating the Foundation Year

Companies should not only select their base year but also document their choice with a clear rationale. Internal approval by sustainability or controlling departments is advisable to ensure that any subsequent adjustments can be transparently justified. In addition, a regular review process is recommended to assess whether rebasing is necessary—for example, in the event of acquisitions, changes in organizational boundaries, or new scientifically recognized emission factors that affect more than approximately 5% of the total corporate carbon footprint.

Companies should also develop a clear rebasing policy early on. This policy specifies when, why, and how a base year may be adjusted—for example, in the event of methodological changes or structural changes within the company.

Related Links

• GHG Protocol – Mitigation Goals
• SBTi – Target Validation Criteria