R to S

REC (Renewable Energy Certificate)

In India, one REC represents 1 megawatt-hour of electricity generated from renewable sources and fed into the grid, under the Central Electricity Regulatory Commission (CERC) REC Regulations, 2022. RECs prove a claim about renewable electricity; they are not carbon credits. Some technologies get a multiplier, so one certificate may not always equal exactly 1 MWh.

Registry

An electronic database that issues, tracks, transfers and retires credits, each with a unique serial number. A registry helps make sure that one credit is sold and used only once.

Removal

Taking greenhouse gases out of the atmosphere and storing them, for example in growing trees, soils or underground storage. A removal is different from a reduction or avoided emission, which only stops new gas from going up.

Residual emissions

The emissions a company or country still has after it has cut everything it reasonably can. Under net-zero standards, only these leftover emissions should be balanced with removals.

Retirement

Permanently cancelling a carbon credit in a registry, so that it cannot be sold again, when someone uses it for a claim. A credit that has not been retired should not be counted.

Reversal

When stored carbon goes back into the air, for example when a forest that earned credits burns down. Programmes use buffer pools or replacement rules to deal with reversals.

SBTi (Science Based Targets initiative)

An organisation that checks whether company emission targets match what climate science says is needed. Its Corporate Net-Zero Standard was first published in 2021; Version 2.0 was published in June 2026, with validations under it from 1 February 2027.

Scope 1 emissions

Direct emissions from sources a company owns or controls, such as fuel burned in its boilers, generators and vehicles, or gases released by its processes (GHG Protocol Corporate Standard, 2004).

Scope 2 emissions

Indirect emissions from the electricity, steam, heat or cooling a company buys. The GHG Protocol Scope 2 Guidance (2015) asks for two figures: one "location-based", using the grid average, and one "market-based", reflecting contracts and certificates the company holds.

Scope 3 emissions

All other indirect emissions in a company's value chain, both upstream (purchased goods, transport, business travel) and downstream (use and disposal of sold products). The GHG Protocol Scope 3 Standard (2011) sorts them into 15 categories, and they are often the largest share.

Sequestration

The process of capturing carbon and storing it, for example when trees take in CO2 through photosynthesis and lock it in wood and roots. How much a tree sequesters varies widely with species, age, site and care.

Sink

Anything that takes in more carbon than it releases, such as a growing forest, healthy soil or the ocean. India's NDC for 2031-2035 aims for a carbon sink of 3.5 to 4.0 billion tonnes CO2e through forest and tree cover by 2035 compared with 2005.