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Abstract

In the Spring of 2021, the mining crackdown in China shook up global Bitcoin mining activity. We show that this crackdown may have reduced the use of renewable electricity sources for Bitcoin mining, resulting in increased carbon intensity of mining activities. We estimate that Bitcoin mining may beresponsible for 65.4 MtCO2 annually, which is comparable to country-level emissions in Greece.
Commentary:
Revisiting Bitcoin’s Carbon Footprint
Alex De Vries,
1
,
2
,* Ulrich Gallersdörfer,
3
,
4
Lena Klaaßen,4,
5
Christian Stoll,4,
6
,
7
Joule Volume 6, Issue 13, P498-502, March 16, 2022. DOI: https://doi.org/10.1016/j.joule.2022.02.005
Abstract
In the Spring of 2021, the mining crackdown in China shook up global Bitcoin mining activity. We
show that this crackdown may have reduced the use of renewable electricity sources for Bitcoin mining,
resulting in increased carbon intensity of mining activities. We estimate that Bitcoin mining may be
responsible for 65.4 MtCO2 annually, which is comparable to country-level emissions in Greece.
1
School of Business and Economics, Vrije Universiteit Amsterdam, The Netherlands
2
Founder of Digiconomist, Almere, The Netherlands
3
TUM Software Engineering for Business Information Systems, Department of Informatics, Technical University
of Munich, Germany
4
CCRI Crypto Carbon Ratings Institute, Dingolfing, Germany
5
Climate Finance and Policy Group, Department of Humanities, Social and Political Sciences, ETH Zurich,
Switzerland
6
MIT Center for Energy and Environmental Policy Research, Massachusetts Institute of Technology, Cambridge,
MA 02139, USA
7
TUM School of Management, Technical University of Munich, Germany
*Correspondence: alex@digiconomist.net
1
Introduction
Although Bitcoin's stature in mainstream finance has grown, its environmental impact remains
uncertain. The increasing attention paid to climate risks and carbon emissions1 has triggered a heated
debate about the sources of electricity used to mine Bitcoin. There are widespread estimates of the share
of renewable electricity sources in the electricity mix that powers Bitcoin mining (see Supplemental
Data Sheet 18), ranging from 39% (according to a survey by the Cambridge Centre for Alternative
Finance or CCAF) to over 58% (according to an industry initiative called the Bitcoin Mining Council)
and even 73% (according to digital assets service provider Coinshares).
Mining is the process of adding new blocks to the Bitcoin blockchain to validate transactions. It involves
a process of trial-and-error that resembles a competitive numeric guessing game in which a correct
guess completes a block and only the winner obtains rewards in the form of both newly minted
Bitcoins and transaction fees. The Bitcoin software automatically adjusts the difficulty of guessing a
correct number to maintain a constant time of 10 minutes between the creation of new blocks. In May
2021, approximately 2.9 million specialized hardware devices worldwide competed in this game,
generating 160 quintillion guesses per second2 and consuming approximately 13 gigawatts (GW) of
electricity (see Supplemental Data Sheet 10 and 11).
In the Spring of 2021, the mining crackdown in China shook up global Bitcoin mining activity. Inner
Mongolia became the first Chinese province to cite environmental concerns as justification for banning
crypto mining in March 2021.3 Between May and June 2021, crypto mining bans were issued in other
Chinese provinces such as Sichuan and Xinjiang, which had historically been hotspots for Bitcoin
mining.4 By the end of June 2021, the crackdown eliminated crypto mining activities within China,
which previously hosted the majority of Bitcoin miners.
In this commentary, we show that this mining crackdown may have increased the carbon intensity of
Bitcoin mining. Based on mining locations and regional carbon emission factors, we found that the
carbon intensity of Bitcoin mining may have increased by 17% in August 2021 compared to the 2020
average. This potential increase highlights the need for stakeholders in the crypto industry to accelerate
the development of strategies to overcome investors' environmental, social, and governance (ESG)
concerns.
Bitcoin’s Mining Footprint
The carbon footprint of Bitcoin mining can be estimated based on electricity sources used by miners.
Previous research outlined different methods for approximating mining locations.4 Based on one of these
approaches, the CCAF regularly generates a map that shows the global distribution of miners (see
Supplemental Data Sheet 8). It is based on Internet Protocol (IP) address information collected from
2
four “mining pools”: BTC.com, Poolin, ViaBTC, and Foundry USA. Collectively, they represent 44%
of total Bitcoin mining activity as of October 2021.5 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% in 2020 to 25.1% 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 gCO2/kWh on average in 2020 to 557.76 gCO2/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 in line 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 plantsthe least efficient form of
coal-fired generation.
Based on average emission factors (557.76 gCO2/kWh) and the Bitcoin network's estimated electric load
demand (13.39 GW as of August 2021), we estimate that Bitcoin mining may be responsible for 65.4
megatonnes of CO2 (MtCO2) per year. Figure 2 depicts the estimated global carbon footprint of Bitcoin
mining, which is comparable to country-level emissions in Greece (56.6 MtCO2 in 2019) and represents
0.19% of global emissions.
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.7 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 gCO2/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 gCO2/kWh, the emission factor
for Alberta is much higher than the Canadian average of 130 gCO2/kWh. Moreover, Quebecwhich
relies almost exclusively on renewable electricity sourcesalready 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.8 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.9
Stranded Fossil Assets Revival
The use of marginal emission factors over average emission factors could have a more significant impact
on the estimates of cryptocurrency emissions. Marginal emissions reflect the change in emissions as a
result of a change to the electric load on a grid. Mining activities increase power demand, which activates
additional electricity generation resources. For example, in New York State, stranded fossil assets (i.e.
assets that can no longer generate an economic return) have been reactivated to power Bitcoin mining
operations. Environmentalists have warned that 30 fossil-fueled power plants in New York State could
be resurrected for mining operations.10 Average emission factors do not properly capture this impact.
As the majority of New York State’s power originates from low-carbon sources, applying average
emission factors therefore underestimates the emissions related to Bitcoin mining in this example.
5
Another U.S. example can be found in Kentucky, which grants tax breaks to attract Bitcoin miners and
thus saves coal companies and creates new jobs.11 According to our calculations, this has led Kentucky
to become the highest-emitting American state in the Bitcoin network (see Figure 3). In addition,
Pennsylvania subsidizes mining company Stronghold Digital Mining to burn coal refuse. Stronghold
Digital Mining has expansion plans and aims to attain a 5% share in the Bitcoin network through this
electricity source12 (Pennsylvania currently represents 0.04% of the global Bitcoin network). However,
to account for cause-effect relationships in detailed electricity system modeling it would be required to
know exact mining locations and load information, but this data is currently unavailable. The estimates
in this commentary were made using average emission factors rather than marginal emission factors.
Figure 3 | Estimated carbon footprint of the Bitcoin network in the United States, as of August 2021. The emission factors
used to calculate the carbon footprint are based on 2019 data due to the limited availability of more recent data. Data and
sources can be found in Supplemental Data Sheet 1.
In the short term, reactivating or prolonging the lifetime of stranded fossil fuel plants or assets to serve
the additional load required by crypto mining operations is likely to continue. Recent attempts to utilize
flare gas in Russia and the United States are other examples of how Bitcoin mining may generate revenue
for companies active in the fossil fuel industry. From an environmental perspective, however, flare gas
utilization to generate electricity results in the same amount of carbon emissions as flaring. For instance,
in the United States, the Environmental Protection Agency requires a minimum flare combustion
efficiency of 98%. Therefore, flare gas utilization projects would only yield climate benefits if the
electricity generated from them replaces electricity generated from higher carbon fuels such as coal or
if they reduce waste gases from venting and leakage.
Conclusion
The decreasing usage of renewable electricity sources for Bitcoin mining following the crackdown in
China highlights the need for stakeholders in the crypto industry to accelerate efforts to decarbonize the
6
industry. Some Bitcoin stakeholders had already signed the Crypto Climate Accord, a private sector-led
initiative launched in April 2021 that represents a commitment to increase the use of renewable
electricity to 100% by 2030. Such commitments may need to be strengthened with compliance
mechanisms to support their credibility.
However, even if the Bitcoin mining industry manages to increase the use of renewable electricity, the
use of the latter for Bitcoin mining is not without its own controversy. In November 2021, the Swedish
Financial Supervisory Authority and Environmental Protection Agency called for a ban on
cryptocurrency mining over concerns that the use of renewable electricity for mining could delay the
energy transition of essential services.13 Furthermore, research on Bitcoin mining has shed light on a
variety of ESG issues.14 While they do not significantly contribute to the carbon emissions generated by
the Bitcoin network, issues such as electronic waste generation cannot immediately be addressed merely
by increasing the use of renewable electricity.
A rapid solution to Bitcoin’s carbon footprint is not within sight. While other blockchain systems rely
on more energy-efficient consensus mechanisms, the likelihood of changing the proof of work
mechanism in Bitcoin is negligible due to its enormous complexity. Even Ethereum, which established
a goal to switch from proof of work to proof of stake since its inception six years ago, still has not fully
migrated to the more energy-efficient alternative. While Bitcoin accounts for roughly two thirds15 of the
total energy demand of all cryptocurrencies, however, more energy-efficient consensus mechanisms
have also elicited environmental concerns. For cryptocurrencies to succeed in mainstream finance, users,
investors and other stakeholders must collectively shift incentives towards the use of more renewable
electricity sources in networks to overcome environmental issues. If this transition succeeds,
cryptocurrencies may provide valuable lessons for other industries and processes that face similar
environmental issues.
References
1. Klaaßen, L., and Stoll, C. (2021). Harmonizing corporate carbon footprints. Nat Commun 12, 6149.
2. de Vries, A., and Stoll, C. (2021). Bitcoin’s growing e-waste problem. Resources, Conservation and
Recycling 175, 105901.
3. Forkast (2021). China’s crypto miners make hard choices to meet climate goals.
https://forkast.news/chinas-crypto-miners-climate/.
4. Stoll, C., Klaaßen, L., and Gallersdörfer, U. (2019). The Carbon Footprint of Bitcoin. Joule 3, 1647
1661.
5. The Block (2022). Latest data shows the US now leads with 35% of Bitcoin’s hash rate.
https://www.theblockcrypto.com/post/120372/us-lead-bitcoin-hash-rate-cambridge.
6. CNBC (2021). New York and Texas are winning the war to attract bitcoin miners.
https://www.cnbc.com/2021/10/09/war-to-attract-bitcoin-miners-pits-texas-against-new-york-
kentucky.html.
7. CNBC (2022). Kazakhstan’s deadly protests hit bitcoin, as the world’s second-biggest mining hub
shuts down. https://www.cnbc.com/2022/01/06/kazakhstan-bitcoin-mining-shuts-down-amid-fatal-
protests.html.
8. Masanet, E., Shehabi, A., Lei, N., Vranken, H., Koomey, J., and Malmodin, J. (2019). Implausible
projections overestimate near-term Bitcoin CO2 emissions. Nat. Clim. Chang. 9, 653654.
9. IEA (2022). Surging electricity demand is putting power systems under strain around the world.
https://www.iea.org/news/surging-electricity-demand-is-putting-power-systems-under-strain-
around-the-world.
10. Associated Press (2021). Bitcoin-mining power plant raises ire of environmentalists.
https://abcnews.go.com/US/wireStory/bitcoin-mining-power-plant-raises-ire-environmentalists-
80618790.
11. Lexington Herald Leader (2021). KY lawmakers want tax breaks for cryptocurrency mining.
But will this create jobs? https://www.kentucky.com/news/politics-
government/article249485805.html.
12. Fortune (2021). New IPO demonstrates why Bitcoin mining is the most stupendously profitable
business on the planet right now. https://fortune.com/2021/10/20/new-ipo-demonstrates-why-
bitcoin-mining-is-the-most-stupendously-profitable-business-on-the-planet-right-now/.
13. Finansinspektionen (2021). Crypto-assets are a threat to the climate transition energy-
intensive mining should be banned. https://www.fi.se/en/published/presentations/2021/crypto-
assets-are-a-threat-to-the-climate-transition--energy-intensive-mining-should-be-banned/.
14. de Vries, A., Gallersdörfer, U., Klaaßen, L., and Stoll, C. (2021). The true costs of digital
currencies: Exploring impact beyond energy use. One Earth 4, 786789.
15. Gallersdörfer, U., Klaaßen, L., and Stoll, C. (2020). Energy Consumption of Cryptocurrencies
Beyond Bitcoin. Joule 4, 18431846.
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China's crypto miners make hard choices to meet climate goals
  • K Le
Le, K. (2021). China's crypto miners make hard choices to meet climate goals. https://forkast.news/chinas-crypto-minersclimate/.
Latest data shows the US now leads with 35% of Bitcoin's hash rate
  • W Zhao
Zhao, W. (2022). Latest data shows the US now leads with 35% of Bitcoin's hash rate. https://www.theblockcrypto.com/post/ 120372/us-lead-bitcoin-hash-ratecambridge.
New York and Texas are winning the war to attract bitcoin miners
CNBC (2021). New York and Texas are winning the war to attract bitcoin miners. https://www.cnbc.com/2021/10/09/war-to-attract-bitcoin-miners-pits-texas-against-new-yorkkentucky.html.
Kazakhstan's deadly protests hit bitcoin, as the world's second-biggest mining hub shuts down
CNBC (2022). Kazakhstan's deadly protests hit bitcoin, as the world's second-biggest mining hub shuts down. https://www.cnbc.com/2022/01/06/kazakhstan-bitcoin-mining-shuts-down-amid-fatalprotests.html.