Article · February 2022 doi: 10. 1016/j joule

Figure 2 | Estimated global carbon footprint of the Bitcoin network, as of August 2021

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Figure 2 | Estimated global carbon footprint of the Bitcoin network, as of August 2021.

The country-level emission factors used to calculate the carbon footprint are based on data from 2019 due to the limited availability of more recent data
Data and sources can be found in Supplemental Data Sheet 1. Since mining pool data from the CCAF represents a limited share of 44% of total Bitcoin mining activity, this limitation introduces uncertainties in estimating emissions. One-off events, such as the 2021 mining crackdown in China or the internet outage in Kazakhstan in 2022, provide empirical insights that can be used to validate the representativeness of the pool data. Before the mining crackdown in China in May 2021, pool data suggested 44% of the total Bitcoin mining activity was taking place in China. Shortly after the crackdown, at the beginning of July, the hashrate of the entire Bitcoin network had decreased by 45% (see Supplemental Data Sheet 17) compared to May 2021. For Kazakhstan, pool data suggested 18% of total Bitcoin mining activity was taking place in the country as of August 2021, while the internet outage at the start of January 2022 resulted in an immediate decrease of 15% in the network hashrate.
Therefore, estimated mining locations based on mining pool data from the CCAF

4 can serve as a proxy for the actual mining locations, even though it may over or underestimate mining activity in certain countries. The mining pool data likely overestimates the share of Bitcoin’s global computational power located in Ireland and Germany. This is because miners can disguise their activities with virtual private networks
(VPNs) and other proxy services if they reside in countries hostile to crypto mining. The CCAF noted that there is little evidence of large mining operations within German and Irish borders. Germany and Ireland both have relatively clean electricity sources compared to other Bitcoin mining locations. Excluding and redistributing the share of Bitcoin's total global computational power located in Germany and Ireland would increase the average emission factor by 3% to 573.51 gCO
/kWh (see Supplemental Data Sheet 6). The average emission factor would likely increase further if a breakdown of mining activities in Canada was considered. Such a specification is currently not available, but it is known that the Black Rock Petroleum Company announced the deployment of up to 1 million Bitcoin mining machines on gas- producing sites in Alberta in July 2021. With a carbon intensity of 790 gCO
/kWh, the emission factor for Alberta is much higher than the Canadian average of 130 gCO
/kWh. Moreover, Quebec—which relies almost exclusively on renewable electricity sources—already limited the power available to crypto miners to 688 megawatts in 2019. Furthermore, emission factors remain a key source of uncertainty in estimates of cryptocurrency emissions.
As there is often a time lag of one to two years until emission factors are published, emission factors over 2019 were used as a proxy for 2021 emission factors. This might slightly over- or underestimate the actual emission factors in 2021. There was, however, no clear upward or downward trend in emission factors over the last two years. The carbon intensity of global power generation grew in 2021 after a decline in 2020 due to surging electricity demand.

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