Bitcoin’s Mining Footprint

2 four mining pools BTC.com, Poolin, ViaBTC, and Foundry USA. Collectively, they represent 44% of total Bitcoin mining activity as of October Mining pools combine the computational power of connected mining devices. By joining pools and sharing rewards, miners can stabilize their revenue stream. In the process, they reveal their IP address, which can be used to establish their location. By matching the estimated mining location data to the carbon intensity of electricity generation at the location, it is possible to visualize how the electricity mix that fuels the Bitcoin network may have evolved. To this end, we considered a global breakdown of mining activities per country and a specification of mining activities within the United States obtained from the CCAF and Foundry USA, respectively.
6
Figure 1 shows that the use of renewable electricity sources may have declined following the mining crackdown in China. We estimate that the share of renewable electricity sources that fuel the Bitcoin network may have decreased from an average of 41.6% into in August 2021.
Figure 1 | Estimated electricity mix that fueled the Bitcoin network from September 2019 to August 2021. The country- level electricity mixes used to calculate the overall electricity mix for the Bitcoin network are based on 2019 data due to the limited availability of more recent data. Data and sources can be found in Supplemental Data Sheet 2.
A possible explanation for this decline is that the Bitcoin network no longer had access to hydropower from the Chinese provinces of Sichuan and Yunnan. Before the crackdown in China, miners seasonally relocated to these provinces to take advantage of their abundant hydropower. After the wet season, they migrated back to coal-dependent provinces, such as Xinjiang and Inner Mongolia. Many miners were previously located in China the seasonal fluctuation can be observed in Figure 1. After the mining crackdown in China, miners primarily migrated to other countries such as Kazakhstan and the United States. Consequently, the share of natural gas in the electricity mix nearly doubled from
15% to 30.8% according to our calculations, and the emission factor of coal-fired power generation potentially increased due to higher-emitting plants in Kazakhstan compared to China. Therefore, the average carbon intensity of electricity consumed by the Bitcoin network may have increased from
478.27 gCO
2
/kWh on average into gCO
2
/kWh in August 2021. Notably, the potential shift from coal resources in China to coal resources in Kazakhstan may have had a major impact on the average carbon intensity of electricity consumed by the Bitcoin network. While

3 the emission factor for coal-generated electricity in China is inline with the global average, the Eurasia region (which includes Kazakhstan) has performed significantly worse (see Supplemental Data Sheet
15). For instance, Kazakhstan mainly burns hard coal, which has the highest carbon content of all coal types. Moreover, it operates numerous subcritical coal-fired power plants—the least efficient form of coal-fired generation. Based on average emission factors (557.76 gCO
2
/kWh) and the Bitcoin network's estimated electric load demand (13.39 GW as of August 2021), we estimate that Bitcoin mining maybe responsible for 65.4 megatonnes of CO
2
(MtCO
2
) per year. Figure 2 depicts the estimated global carbon footprint of Bitcoin mining, which is comparable to country-level emissions in Greece (56.6 MtCO
2
in 2019) and represents
0.19% of global emissions.

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