Emission Reduction Unit

The Emission reduction unit (ERU) is a trading unit under the Kyoto Protocol representing a reduction of greenhouse gases under the Joint Implementation mechanism, where it represents one tonne of CO₂ equivalent reduced.

To allow comparison between the different effects of gases on the environment, scientists have defined multipliers for gases that compare their greenhouse potency (global warming potential) relative to that of carbon dioxide.

One example of a Joint Implementation project resulting in an emission reduction unit, is the production of biogases by landfill sites. These gases consist of mainly methane which escapes to the atmosphere if it is not collected. The main reason for dealing with methane is that it has a 100-year global warming potential multiplier of 25 compared to carbon dioxide (i.e. has 25 times the greenhouse potency). Collection of methane is usually accompanied by its combustion. Burning one tonne of methane produces nearly 3 tonnes of CO₂, thus reducing its greenhouse effect by (25-3=22) ERU.