Emission Reduction Unit

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Emission reduction unit (ERU) refers to the reduction of greenhouse gases, particularly under Joint Implementation, where it represents one tonne of CO2 equivalent reduced.

It is well known that emission of carbon dioxide is the main cause of global warming (via the greenhouse effect). However other gases also play a role in atmospheric warming. For instance, older refrigerators and air conditioners used chlorofluorocarbons (CFCs), which are often more potent greenhouse gases than carbon dioxide.

To allow comparison between the different effect 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.

Regarding emission reduction units, one example 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 multiplier of 21 compared to carbon dioxide (i.e. has 21 times the greenhouse potency). Collection of methane is usually accompanied by its combustion. Although burning methane produces carbon dioxide, its greenhouse effect is reduced by 20 ERU (i.e. 21 times carbon dioxide to 1 times carbon dioxide).