How CO2e calculations work

CO2e - Methods of Calculation

Human activities don't just emit carbon dioxide (CO2) but also a variety of other greenhouse gases that heat up the atmosphere.

Emission accounting largely happens in carbon dioxide equivalents (CO2e) (opens in a new tab), so a way of converting the other gases into CO2e is needed. This is done by assigning each gas (referred to as "constituent gases" here) a Global Warming Potential (opens in a new tab) (GWP), which in essence means "how many kg of CO2 would one kg of this gas correspond to." You can read more about emission factors and GWP in our introduction to emission factors.

As models and data have improved, our best guess of the Global Warming Potential of the different gases have changed. The calculation methods that used for these GWP are the IPCC (opens in a new tab)'s Assessment Reports. The Assessment Reports are generally shortened to "AR", so the "4th Assessment Report" becomes "AR4"

The last three Assessment Reports released were:

  • AR4 (2007)
  • AR5 (2014)
  • AR6 (2021)

At Climatiq we aggregate data from a wide variety of sources that use different calculation methods. We will always inform you what calculation method our calculated CO2e is based on. Take the following example of a response from the /estimate endpoint:

"co2e": 0.31875,
"co2e_unit": "kg",
"co2e_calculation_method": "ar4",
"co2e_calculation_origin": "source",
"constituent_gases": {
"co2e_total": 0.31875,
"co2e_other": null,
"co2": null,
"ch4": null,
"n2o": null
//... more

You will see a co2e_calculation_method field, and calculation_origin field. You can see that this particular estimate is calculated with the methodology from the 4th Assessment Report (ar4), and that the CO2e has been calculated by the source.

Climatiq-calculated CO2e

Not all CO2e values are calculated by the source - some are calculated by Climatiq. We do this if we have enough data to provide it and the source has not provided it pre-calculated (for example, emission factors from the US Environmental Protection Agency)

An example, if the source:

  • Specifies all constituent gases used for their calculations
  • Uses those gases based on the ar4 calculation method to calculate a co2e

Then Climatiq has enough data to also calculate CO2e with the help of the ar5 method. You can make an estimation with the following parameters to get the more recent AR5 numbers:

// /estimate endpoint
"emission_factor": {
"activity_id": "some-activity-id",
"calculation_method": "ar5"
"parameters": {
"distance": 10,
"money_unit": "km"

And you will get the following response back

"co2e": 2.9658171172938,
"co2e_unit": "kg",
"co2e_calculation_method": "ar5",
"co2e_calculation_origin": "climatiq",
"constituent_gases": {
"co2e_total": null,
"co2e_other": null,
"co2": 2.9328720167999998,
"ch4": 0.1180605261,
"n2o": 0.11184681419999999
// ... other fields

The key differences here are that the co2e_calculation_method has switched to ar5, and the co2e_calculation_origin has gone from source to climatiq


Climatiq tries to stay as close to the sources as possible.

This means that we will always default to providing the CO2e emission factor provided by the source, preferring the most recent calculation method if the source provides more than one.

If you want to make your own choice about which calculation methodology to use, Climatiq allows you to define calculation_method in all endpoints that accept a Selector.

Possible Returned Calculation Method Values

The co2e_calculation_method field is a standard part of Climatiq's API responses. Below is a table that describes potential values for this field across Climatiq endpoints.

Due to the need for backwards compatibility, there are multiple values that mean the same. You should check the documentation of the endpoint to see which version it uses or ensure your applications can recognize and handle both versions of each value.

Endpoints will always list the values it might return. Climatiq might add new values as a non-breaking change, e.g. when a new Assessment Report is released. Your application should not treat this list as exhaustive.

DescriptionOlder valueNewer value
CO2 equivalents calculated over a 100-year timespan using the 4th IPCC Assessment Report (AR4).ar4ipcc_ar4_gwp100
CO2 equivalents calculated over a 100-year timespan using the 5th IPCC Assessment Report (AR5).ar5ipcc_ar5_gwp100
CO2 equivalents calculated over a 100-year timespan using the 6th IPCC Assessment Report (AR6).ar6ipcc_ar6_gwp100
CO2 equivalents calculated over a 100-year timespan using a combination of different IPCC Assessment Reports. This is used when multiple emission factors are involved and they do not align under a single report.mixedipcc_mixed_gwp100