Base Year
A base year is the reference year against which an organization measures its greenhouse gas emission reduction progress. It establishes the starting-point emissions level from which percentage reductions are calculated, and it must be recalculated when significant structural changes (mergers, acquisitions, divestitures) occur.
The base year anchors all reduction targets and progress claims. If a company sets a target to reduce emissions 42% by 2030, the base year inventory is the number from which that 42% is measured. SBTi requires base years to be no earlier than 2015 and recommends the most recent year with reliable data.
Base year recalculation is triggered by structural changes that would distort year-over-year comparisons: mergers and acquisitions, divestitures, changes in calculation methodology, discovery of significant data errors, or changes in reporting boundary (e.g., adding a Scope 3 category). The GHG Protocol specifies that organizations should establish a base year recalculation policy with a significance threshold (typically 5–10%).
Proper base year management requires: maintaining detailed records of the original base year inventory, documenting the recalculation policy, applying recalculations consistently, and communicating changes transparently to stakeholders.
Carbon accounting platforms that maintain historical data with full audit trails make base year recalculation manageable. Gravity preserves all historical calculations, factor selections, and source data, enabling accurate recalculation when structural changes occur.
Frequently asked questions
What is a base year in carbon accounting? +
A base year is the reference year against which emission reduction progress is measured. For example, a “42% reduction by 2030 from a 2020 base year” means cutting emissions to 58% of the 2020 level. SBTi requires base years no earlier than 2015.
When should you recalculate the base year? +
Recalculate when significant structural changes occur: mergers, acquisitions, divestitures, methodology changes, major data corrections, or reporting boundary changes. The GHG Protocol recommends a significance threshold of 5–10%.
Related terms
Carbon Accounting
Carbon accounting is the systematic process of measuring, recording, and reporting the greenhouse gas (GHG) emissions produced by an organization, product, or activity. It follows standardized methodologies — most commonly the GHG Protocol — to quantify emissions across Scope 1 (direct), Scope 2 (purchased energy), and Scope 3 (value chain) categories, producing an auditable inventory that underpins disclosure, reduction planning, and regulatory compliance.
SBTi (Science Based Targets initiative)
The Science Based Targets initiative (SBTi) is a partnership between CDP, WRI, the UN Global Compact, and WWF that defines and validates corporate greenhouse gas reduction targets consistent with the Paris Agreement goal of limiting warming to 1.5°C above pre-industrial levels.
GHG Protocol
The GHG Protocol is the world's most widely used greenhouse gas accounting standard. Developed by the World Resources Institute (WRI) and the World Business Council for Sustainable Development (WBCSD), it provides frameworks for organizations, cities, and countries to measure and manage their emissions across three scopes.
Net Zero
Net zero means reducing greenhouse gas emissions as close to zero as possible, with any remaining residual emissions balanced by an equivalent amount of carbon removal from the atmosphere. The SBTi Corporate Net-Zero Standard requires at least 90–95% absolute emission reductions before carbon removals can be used.