Chapter 32 Exercises: The Environmental Debate: Energy, E-Waste, and Sustainability

Exercise 1: Energy Consumption Contextualization (Apply)

Using the CBECI best estimate of ~150 TWh/year for Bitcoin:

(a) Calculate Bitcoin's energy consumption as a percentage of global electricity consumption (~28,000 TWh/year as of 2025). Express your answer to two decimal places.

(b) The average US household consumes approximately 10,500 kWh per year. How many US households could be powered by Bitcoin's annual energy consumption? Show your work.

(c) Critically evaluate the comparison you just made in part (b). Why is "number of households that could be powered" a potentially misleading framing? Consider whether the energy Bitcoin consumes would actually be available to those households if mining ceased.

Expected outcome: Part (a) should yield approximately 0.54%. Part (b) should yield approximately 14.3 million households. Part (c) should discuss the difference between baseload energy, the geographic distribution of mining, stranded energy, and the fact that "could power X homes" implies a direct substitutability that does not exist in real energy markets.

Exercise 2: Carbon Footprint Estimation (Analyze)

Suppose the following simplified model of Bitcoin mining geography and energy mix:

(a) Calculate the weighted average carbon intensity of Bitcoin mining (in g CO2/kWh).

(b) Using the total energy consumption of 150 TWh/year and your weighted average from (a), estimate Bitcoin's annual CO2 emissions in million tonnes.

(c) Discuss how the "Other/Unknown" category — which you assigned the global grid average — could significantly change your estimate. What would the total CO2 estimate be if "Other/Unknown" were entirely coal (900 g CO2/kWh)? What if it were entirely hydro (30 g CO2/kWh)?

(d) Explain why the uncertainty in the "Other/Unknown" category is not just a data inconvenience but a fundamental limitation of all Bitcoin carbon footprint estimates.

Exercise 3: The Energy Per Transaction Debate (Evaluate)

A journalist writes the following in an article: "Each Bitcoin transaction consumes 1,360 kWh of electricity — enough to power the average American home for 47 days. Meanwhile, a Visa transaction uses just 0.002 kWh. Bitcoin is literally a million times worse for the environment than conventional payments."

(a) Identify at least four specific errors, misleading framings, or missing context in this statement.

(b) Rewrite the comparison in a way that is technically accurate and intellectually honest, while still conveying the genuine scale of Bitcoin's energy consumption.

(c) Now steelman the journalist's core point. Even after correcting the technical inaccuracies, is there a legitimate environmental concern embedded in the original claim? Articulate it precisely.

Exercise 4: The Stranded Energy Thesis (Analyze)

Crusoe Energy Systems deploys Bitcoin mining containers at oil well sites to consume natural gas that would otherwise be flared (burned without generating useful energy) or vented (released directly as methane into the atmosphere).

(a) Methane has approximately 80x the global warming potential (GWP) of CO2 over a 20-year timeframe. If a well site vents 1,000 cubic meters of methane per day, and Crusoe's mining operation instead burns that methane to generate electricity for mining (producing CO2 instead of releasing CH4), calculate the net reduction in CO2-equivalent emissions per day. Assume: 1 m3 of methane = 0.68 kg, and combustion converts each kg of CH4 into 2.75 kg of CO2.

(b) Does this calculation mean that Bitcoin mining at flared gas sites is environmentally beneficial (net positive for the climate)? Or merely less harmful than the alternative? Articulate the distinction carefully.

(c) What percentage of total Bitcoin mining currently operates at flared gas sites? Is the stranded energy argument representative of Bitcoin mining as a whole, or is it an edge case being used to justify the broader industry's energy consumption?

(d) Propose a policy framework that would maximize Bitcoin mining's use of stranded energy while discouraging mining that consumes grid electricity from fossil fuel sources. What incentives and penalties would you include?

Exercise 5: Proof of Stake Energy Comparison (Apply)

(a) Ethereum's pre-Merge energy consumption was approximately 85 TWh/year. Post-Merge, it is approximately 0.01 TWh/year. Calculate: - The absolute energy savings in TWh - The percentage reduction - The equivalent number of US households that could be powered by the saved energy (using 10,500 kWh/year per household)

(b) If Bitcoin hypothetically achieved the same percentage energy reduction by switching to Proof of Stake, what would its new annual energy consumption be? Express in both TWh and kWh.

(c) Bitcoin maximalists argue that this hypothetical is irrelevant because Proof of Stake provides a fundamentally different (and inferior) security model to Proof of Work. Summarize their argument in two to three sentences, then evaluate whether the security trade-off justifies the energy difference. Clearly state the values assumptions underlying your evaluation.

Exercise 6: E-Waste Lifecycle Analysis (Analyze)

An Antminer S21 ASIC miner weighs approximately 15 kg and has an estimated economically useful lifespan of 3-5 years (after which it is no longer profitable to operate due to newer, more efficient hardware).

(a) If the Bitcoin network has approximately 3.5 million active ASIC units with an average lifespan of 4 years, estimate the annual e-waste generated in tonnes.

(b) Compare this to the global annual e-waste generation of approximately 62 million tonnes (2022 UN estimate). What percentage does Bitcoin ASIC waste represent?

(c) Why is the Bitcoin ASIC e-waste problem qualitatively different from general consumer electronics e-waste? Consider the following factors: - Repurposability of the hardware - Geographic distribution of the waste - Composition of the waste - Regulatory coverage

(d) Propose two concrete engineering solutions that could reduce ASIC e-waste by at least 50% without reducing mining efficiency. Explain the trade-offs of each solution.

Exercise 7: Mining Geography Simulation (Create)

Using the carbon_calculator.py script provided with this chapter (or designing your own calculation):

(a) Model three scenarios for Bitcoin mining's geographic distribution in 2030: - Scenario A (Green Shift): 70% of hashrate in regions with <100 g CO2/kWh, 20% in moderate regions (100-400 g CO2/kWh), 10% in high-carbon regions (>400 g CO2/kWh) - Scenario B (Status Quo): Current distribution remains roughly unchanged - Scenario C (Race to the Bottom): Mining migrates to the cheapest electricity regardless of carbon intensity: 15% low-carbon, 35% moderate, 50% high-carbon

(b) For each scenario, estimate the annual CO2 emissions (in Mt) assuming total energy consumption of 180 TWh (projected growth).

(c) What policy interventions could shift the trajectory from Scenario C toward Scenario A? Be specific about which governmental bodies would implement which policies.

Exercise 8: The Value Question (Evaluate)

This is the culminating exercise. It requires you to synthesize the data from the entire chapter and make a reasoned judgment.

(a) Articulate the strongest possible argument that Bitcoin's energy consumption is justified. Use specific data from this chapter. Your argument should be strong enough that a reasonable environmentalist would need to pause and consider it seriously.

(b) Articulate the strongest possible argument that Bitcoin's energy consumption is unjustified. Use specific data from this chapter. Your argument should be strong enough that a reasonable Bitcoin advocate would need to pause and consider it seriously.

(c) State your own position. Which argument do you find more persuasive, and why? Identify the specific values assumptions and empirical claims underlying your position.

(d) What single piece of evidence or data point, if it existed, would change your mind? (If nothing could change your mind, acknowledge that your position is not evidence-based but values-based, and explain why you hold those values.)

Exercise 9: Blockchain for Sustainability — Critical Assessment (Evaluate)

Choose one of the following blockchain-for-sustainability use cases: - Carbon credit tokenization (e.g., Toucan Protocol, KlimaDAO) - Renewable Energy Certificate tracking (e.g., Energy Web Foundation) - Supply chain provenance for ESG compliance (e.g., Circulor, IBM Food Trust)

(a) Research the current status of the project you chose (use information from this chapter and any additional sources). Is it operational and at scale, or still in pilot/proof-of-concept phase?

(b) Identify the specific problem the blockchain component solves. Could the same problem be solved by a centralized database with cryptographic audit trails? If so, what (if anything) does the blockchain add?

(c) Calculate or estimate the environmental cost of the blockchain platform itself (energy consumption of the underlying chain, hardware requirements for nodes). Compare this to the environmental benefit claimed by the application.

(d) Deliver a verdict: Does the net environmental impact of this blockchain application justify its existence? Support your conclusion with specific evidence.

Exercise 10: Debate Preparation (Create)

Your class is holding a structured debate with the motion: "This house believes that Proof of Work mining should be banned in countries that have committed to net-zero emissions targets."

(a) Prepare a 3-minute opening statement for the proposition (in favor of the ban). Include at least three data points from this chapter and anticipate the strongest counterargument.

(b) Prepare a 3-minute opening statement for the opposition (against the ban). Include at least three data points from this chapter and anticipate the strongest counterargument.

(c) Regardless of which side you personally agree with, identify the single strongest argument from the side you disagree with. Explain why it is strong and how you would respond to it in a rebuttal.