Improving Commons Carbon Calculations

Starting in February, Commons is updating our carbon weights annually to align with the Supply Chain Greenhouse Gas Emission Factors from the US Environmental Protection Agency (EPA).

In the past few years, the EPA has begun to release annual updates to this dataset. The latest update was in April 2023. Switching from our current dataset to the US EPA’s factors will enable Commons carbon calculations to be more up-to-date and easier to update each year.

With the switch to the EPA’s new GHG factors, Commons users’ footprint estimates will reflect the most recent data, and they can expect to see a decrease in their emissions calculations due to updated accounting practices and systemic emissions reductions over the past decade. 

Read on to learn more about how Commons calculates carbon footprints and the implication of the update to our carbon datasets.

Commons’ Carbon Data Sources

The US Environmentally-Extended Input-Output (US EEIO) model is a national-level dataset from the EPA that's a foundational data source for Common’s carbon footprint calculations

The US EEIO combines macroeconomic data with the US’s National Greenhouse Gas Inventories to provide a per-dollar estimate of carbon emissions across 411 US industry sectors, like apparel and furniture. 

These estimates include “upstream” carbon impacts, such as emissions from raw material extraction, transportation, and manufacturing. Unlike other Life Cycle Assessment (LCA) methods, the US EEIO model does not account for the environmental impacts of the construction of fixed capital assets. Fixed capital assets are things like buildings, machinery, and software, which companies use to produce their goods and services.

To make up for the absence of capital assets impacts from the EEIO model, Commons has historically used an innovative dataset from Yale called the Capital-Inclusive Footprint Tool for the United States (CIFT-US) to construct the carbon weights we use to estimate the emissions from your spending. CIFT-US builds upon the USEEIO by integrating the environmental impacts from fixed capital assets into the calculation of the environmental footprints of goods and services. However, Yale no longer actively maintains this dataset.

As part of our switch to US EPA’s annual factors, Commons will no longer use CIFT. While this will mean that capital asset emissions are no longer included in Commons' carbon impact calculations, Commons can now use the most recent available data to inform consumer choices.

Why We’re Updating Our Carbon Weights

The switch to the EPA’s regularly updated Supply Chain GHG Factors will enable the Commons team to calculate users’ footprints more accurately based on the latest data available. The most recent data was released in 2023, based on 2021 dollars and 2019 greenhouse gas emissions. Users’ emission data from all past and future transactions will be updated using this dataset.

We’re updating the calculations for past transactions because there are notable shifts in the calculations — more on that below. By recalculating all transactions using the EPA’s factors, users can reliably compare their entire carbon history.

In the future, we anticipate making periodic updates to the dataset as the US EPA data is revised, resulting in much smaller differences year over year. 

How New Carbon Weights Will Affect Carbon Calculations

As a result of this data update, we project that the average Commons user’s footprint estimate will decrease by about 20%. There are two key drivers of this decrease: 

1. Systemic decarbonization over time

Commons’ current dataset uses the EEIO’s GHG data from 2013. Over the past ten years, the U.S. has reduced its annual emissions from about 5.5B tons to 5.0B tons, and annual per-capita emissions have decreased from about 17.5 to 15.5 tons. 

These emissions reductions are a result of systemic decarbonization efforts like energy efficiency and the adoption of renewables. Because the new EPA dataset uses GHG data from 2019, it will better reflect these decarbonization efforts. Over time as we update to the EPA’s latest data, more systemic decarbonization will be reflected in the user calculations.

2. Excluding fixed capital assets from consumer calculations 

As mentioned above, our previous dataset used CIFT to account for the emissions of fixed capital assets (like companies’ machinery and software) in consumers’ footprints. The EPA’s factors exclude the emissions of fixed capital assets, as is the industry standard. 

Our switch to EPA’s annual factors will remove the allocation of fixed capital asset emissions from users’ footprints.

The Commons carbon team is excited about how the EPA’s annual GHG factors will give users access to more timely, accurate carbon accounting. 

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