CO2 reduction strategies comparison

Common strategies and common sense in carbon dioxide reduction

Please note, this is a work in progress. I will continue to update as I get time!

A cost-benefit comparison of some things that you can do to stop global warming

1. Introduction

1.1 Motivation

Have you ever been to a restaurant that didn’t put the prices on its menu?

There are many things we can do to help the environment, and help stop global warming. Here’s something that’s more difficult: to decide what the best ways are, what the most cost-effective ways are, instead of going in blind. Lacking good data, there’s that uneasy feeling, as if we just sat down to order at a restaurant that chose not to list the prices.

I couldn’t find a reasonable cost-benefit analysis of many of the actions we could take. So I’m going to try to do the calculations myself.

The main metric will be dollars spent per tonne of CO₂ saved; I will also calculate the dollar cost for the average person (in a first-world country) to reduce their CO₂ consumption down to the annual CO₂ budget, if we were to use that strategy alone.

There will be other actions that we can take that do not fit into this analytical framework of dollars/tCO₂, but we can still try to quantify how much CO₂ they save, to help us decide whether the actions are worth taking or not.

This is not intended to be a discussion of cutting edge research. Instead, the point is to focus on actions that can be taken by most of us.

1.2 Disclaimer

Here are my credentials for this task: I don’t have any.

Don’t take my word for anything. I’ll try to show my calculations, so if there are any mistakes it should be easy to point them out. All corrections and suggestions gratefully accepted.

1.3 The ideas I looked at

Here’s a list of some of the possible actions that were considered.

Hybrid cars
Electric cars
Buying a smaller car
Heat-sink (“geothermal”) AC/heating
Tankless water heaters
Rooftop solar panels
Green electricity from the power grid
Saving forests or planting trees
Carbon offsets
Carbon capture
Biofuels
LED bulbs
House insulation
Energy efficient appliances
A vegetarian diet
Local food
Cycling instead of driving
Flying less often

2. Summary

(In case you have dinner cooking on the stove and don’t want to read too much further.)

This table summarizes the results, so you don’t have to read the details below if you don’t want to. For each strategy, it provides the following information:

cost, using two different metrics: (a) dollars per tonne of CO2, and (b) the amount it would cost to go from the average US person to bring their CO2 consumption down to a sustainable carbon budget
cost or savings using other measures, for strategies that don’t fit the $/tCO2 metric
additional benefits and drawbacks that can’t be quantified easily

S. No.	Strategy	Savings	Other benefits and drawbacks
1	Hybrid cars: in this case, hybrid Civic vs. regular Civic	$100/tCO₂, 3 months carbon budget / $100	Hybrid batteries use rare-earth metals, have environmental consequences
2	Toyota Highlander, hybrid vs regular	$800/tCO₂, 12 days carbon budget / $100	Hybrid batteries use rare-earth metals, have environmental consequences

3. Some useful numerical values

Parameter	Value	References	Comments
CO₂ budget per person	Approximately 3 tonnes per person	link	In most plans, the carbon budget starts higher and gradually drops. 3 tonnes per person is a very rough approximation of the midpoint of this process. This is the combined emissions from personal spending on housing, travel, food, products and services.
CO₂ produced per capita, per year	Approximately 16 tonnes per person, per year (USA)	link	For comparison, approx 5 tonnes per person per year (China), 1 tonne per person per year (India)
Effect of carbon taxes	A tax of $25/tCO₂ would add 21 cents per gallon to the price of gasoline, 1.2 cents per kW-hour for electricity from non-renewable sources.	link	Please note that carbon taxes have severe flaws as way of remediating damage due to global warming. See chapter 4 of this article, or also this discussion: link
CO₂ emission per unit of electricity	4.5 × 10^-4 tonnes/kW-hour	link	This calculation does not include line losses, or other gases such as methane. These are not significant at the level of accuracy that we will be working with.
CO₂ per liter of gasoline burned	2.2 × 10^-3 tonnes CO₂ per liter	link	8.9 × 10^-3 tonnes CO₂ per gallon
CO₂ to carbon conversion	3.7 tonnes of CO₂ = 1 tonne of C	Ratio of the atomic weight of CO₂ to the atomic weight of C	Some sources give the carbon budget, while others give the CO₂ budget. This is useful in converting between them. We will use CO₂ for all calculations.
CO₂ per kilometer of air travel	0.2 kg CO₂ per mile (!)	link

4. Why should we care?

Obviously, this section is more personal and less quantitative. And it’s not the purpose of this article to get into details of the enormous effects of global warming on people and the environment. There’s already plenty of research about that, for example here and here and here and here and here.

However, I would like to point out is that pure economic analyses of the costs of global warming are inadequate; and that levying carbon taxes as a way of solving the problem can also be inadequate. A lot of the analyses of the effects of global warming actually understate the moral imperative to combat it, especially by residents of first-world nations.

There are huge non-economic affects of global warming, such as habitat loss and species extinction.
Global warming is not just shunting money from poorer regions to wealthier ones. It’s shunting money from the victims of global warming to the agents of global warming.
Related to the previous point, the financial estimates of the harm done are not commensurate with the actual devastation. For example, take someone who gets two meals a day: if they are deprived of one of these meals, this gets counted as just a dollar or two of harm, but the actual damage would be considerable.
The people who are harmed do not have the choice whether or not to accept the change to their lives. For example, they may be forced to move from a land where they have lived for many generations, or abandon the only livelihood they know how to make; this is a fundamental uprooting that most of them would prefer not to do, whether or not they are compensated for it.
Borders are not open. Climate change may lead to some areas being less habitable and other areas more, with a smaller net effect. However, people who are badly affected do not have the choice to move to other places, even if they wanted to.
The money collected by carbon taxes is not distributed to the people who are most harmed by the affects of global warming. In particular, the tax money goes to the government where the economic activity happens, but the harmful effects are felt worldwide, and predominantly in regions with lower economic activity. So even with a carbon tax, there is a net effect of shunting money from poorer regions to wealthier ones.
The numbers actually used as carbon taxes in practice are influenced heavily by political factors separate from the actual social cost of the carbon. In particular, it cannot be set more than can be accepted by the politicans and populace.
The carbon tax is considered by many politicians to have repercussions on the economy, and is set lower than the expected social cost of carbon in order to take these repercussions into account.
Once the changes from global warming have been effected, they can last a very long time, accumulating damage. Therefore, actual prevention is much more valuable than remediation.
The estimates of the cost of global warming that carbon taxes are based on, are calculated by discounting future costs. That is, something that would harm a future generation $100, is given a cost of, say, $50, as it is assumed that we do not care as much about affects in the future. The moral hazards of this should be obvious.

5. Calculations for individual cases

5.1 Hybrid cars and other fuel-efficient cars:

5.1.1 Honda Civic vs. Honda Civic Hybrid

Assume that the fuel efficiency of a hybrid car (such as a Toyota Prius or a Honda Civic hybrid) is 50 miles/gallon $\approx$ 20 km/liter of gasoline, and that a gasoline-driven Honda Civic gets 35 miles/gallon, which is about 14 km/liter.

There are a couple of different ways of calculating this. We’ll do it both ways to see if they agree with each other as a sanity check. The first is by using “true cost of ownership” from Kelly Blue Book (kbb.com) or Edmunds (edmunds.com) to determine the costs, while the second is by simply using the upfront costs. The first method aims to be more accurate, while at the same time has more assumptions built into it.

5.1.1.1 Calculation using “true cost of ownership”

We will do the calculations for a distance driven of 75,000 miles, which is 120,000 km. (The reason for choosing this particular number is that Edmunds calculates the total cost of ownership over this distance.)

Over this distance, the car will use approximately $120,000 km/(20 km/liter) = 6,000 liters$ of gasoline. This translates into $6 \times 10^3 \times 2.2 \times 10^{-3}$ tonnes of CO₂ over the lifetime of the vehicle, or 13.2 tonnes of CO₂.

For a conventional car, the number of tonnes of CO₂ over the calculation period of the car would be $(120,000 km \div 14 km/liter) \times 2.2 \times 10^{-3} tCO_2/liter$ = 19 tonnes of CO₂.

Therefore, the savings of gasoline over 120,000 km are 6 tonnes of CO₂.

To find the dollar cost for that savings in gasoline, we will use the Edmunds total cost of ownership. For that distance (5 years at 15,000 miles per year), the total cost of ownership for the Honda Civic is $32,000, while that for a Honda Civic Hybrid is $33,300.

Therefore, the cost per tonne of CO₂ is (33,300 – 32,000)/6 = $200/tonne of CO₂.

5.1.1.2 Calculation using direct costs

Assume that the life of the car is 150,000 mi or 250,000 km.

Number of tonnes of CO₂ over this lifetime for a regular car: $250,000 \times 2.2 \times 10^{-3} \div 14$ = 40 tCO₂.

For a hybrid, by the same calculations, this number is 27.5 tCO₂. So the difference is approximately 12 tCO₂.

From Edmunds.com, we estimate the extra cost of a hybrid at $5,000. We will assume that the price of gas is $3/gallon.

Over the full lifetime of 150,000 miles, the gasoline car will use 150,000/35 = 4300 gallons of gasoline. The hybrid will use 150,000/50 =3000 gallons.

The savings in gas will recoup 1300 * 3 = $3900 dollars of the difference in cost. The savings in CO₂ emissions will be $1300 \times 8.9 \times 10^{-3} \approx 12 tonnes$ .

By this calculation, the efficiency of buying a hybrid is $(5000-3900) \div 12 \approx$ 100/tCO₂$. These calculations are very sensitive to the difference in price; if it were $6000 rather than $5000 the answer would be approximately $200/tCO₂.

5.1.2 Toyota Highlander vs Toyota Highlander Hybrid

This cost per tonne is very sensitive to the gas mileage of the cars. It makes sense to repeat this calculation for a “typical” SUV. We choose the Toyota Highlander.

mileage	total cost of ownership (120,000 km)	tonnes of CO_{2 (120,000 km)}
Toyota Highlander	18/24 mpg	$41,903	33 tonnes CO₂
Toyota Highlander Hybrid	28 mpg	$49,878	23 tonnes CO₂

This gives a cost per tonne of CO₂ of (50,000-42,000)/(33-23) = $800/tCO₂. Note that if we use Kelley instead of Edmunds, it is $600/tCO₂.

5.1.3 Drawbacks other than CO₂ emissions

There are significant drawbacks to hybrid and electrical cars that are not reflected here: batteries can be pretty messy and energy intensive to manufacture. By most analyses, this extra cost to manufacture is not large compared to the savings from the added energy efficiency ([4], [5]).

5.2 Electric cars

For electric cars, there are two important cases to consider: the electrity can come from fossil fuels, or it can come from renewable (carbon-neutral) sources.

The carbon cost of an electric car comes from two parts: the cost to manufacture, and the carbon cost of the electricity. For hybrid and gasoline cars, the second cost dominates, but for electric cars both have to be taken into consideration ([4], [5]). Note that if the manufacturer derives its electricity from renewable sources, that part also vanishes, but we assume that this is not the case.

5.2.1 Charging from fossil fuel sources

The ratings for US electric cars are given in MPGe, or miles per gasoline equivalent: the distance travelled for a charge of electricity equivalent to the energy of one gallon of gasoline. This amount of energy is 33.7 kW-hours.

Remember that carbon cost of electricity is $6.9 \times 10^{-4}$ tonnes of CO₂ per kW-hour.

We will choose the Nissan Leaf as a representative for electric cars. For this vehicle, the fuel economy is 114 MPGe, or 30 kW-hours/100 mi.

For this vehicle, the Edmunds True Cost to Own for the standard 5 year/15,000 miles per year situation is $23,000. This takes into account a tax credit of $7,500. The Kelley Blue Book estimate of the total cost of ownership is $35,835, which is $28,000 if you consider the tax credit. We will choose a value of $25,000.

It’s tough to decide what exactly to compare this to. We’ll choose a Honda Civic as the closest equivalent. As mentioned above, the Edmunds True Cost to Own is $32,000, and it emits 19 tonnes of CO₂ over the calculation period.

For the Nissan Leaf, the amount of CO₂ emissions to travel 75,000 miles is $75,000 miles * 0.3 kW-hours/mile * 6.9 * 10^{-4} tCO_2/kw-hour$ . This is 15.75 tonnes of CO₂.

So the Nissan Leaf gets 114 miles per energy equivalent of a gallon of gasoline, while the Honda Civic Hybrid gets 45 miles per gallon of gasoline, yet the Nissan Leaf creates approximately the same CO₂ emissions per mile. This was certainly a surprise. Presumably this has to do with the inefficiencies of burning fossils fuels and converting to electricity — or the numbers used from the EPA, for CO₂ emitted per gallon of gasoline and per kW-hour of electricity, may be inaccurate. Also note that this disagrees with the numbers from the reference [5], but I don’t know how they obtain their numbers.

(As a check of this rather startling conclusion, note that one gallon of gasoline is equivalent to 33.7 kW-hours of electricity. So the amount of CO₂ emissions per 1MW-hour of gasoline is 8.9 kg CO₂/gallon * 1 gallon/33.7 kW-hours * 1000 kW-hours/1MW-hour * 1 tonne/1000 kg = 0.26 tonnes/MW-hour. But the value used for electricity is 0.69 tonnes/MW-hour. I do not have an explanation why electricity is so much more expensive other than inefficiencies of generation and conversion.)

Therefore, over a 75,000 mile ownership, the Nissan Leaf saves $7,000 and also saves approximately 3 tonnes of carbon dioxide. If the $7,500 tax credit is taken away, owning a Nissan Leaf has an efficiency of $500/3 = $166/tCO₂. Again, this number is extremely sensitive to the estimate of the total cost of ownership, and also the cost of the car we’re comparing it with, so this number does not have a high degree of significance. It does, however, seem robust to say that the price of the car is competitive with comparable cars, and will save a few tonnes of CO₂.

5.2.2 Charging from renewable sources

Of course, the electricity used for recharging the electric car batteries may be obtained from renewable sources. In this case, the only emissions are those used in producing the car and battery. The above reference provides a value of 8.8 tCO₂ for this, which is approximately 3 tCO₂ more than for a gasoline powered car.

However, note that the cost of electricity will then be slightly higher, thereby increasing the total cost of ownership.

Over 150,000 miles, the number of kW-hours used would be 150,000 miles * 0.3 kW-hours/mile = 45,000 kW. The average price of electricity per kilowatt-hour in the US is $.13/kW, rising to $.20/kW in New England (see [6]. If we choose to use electricity sourced from green sources, the extra cost is 2.4 cents per kilowatt-hour.

5.3 Heat Sink (“Geothermal”)

Make an estimate of the savings in terms of gas; find the amount of gas used without this; and electricity for air-conditioning. How much extra electricity gets used? We will need the lifetime of a system. Check the book, and the article mentioned in the email.

5.4 Solar panels

Costs of making it, including environmental costs, and water.

Lifetime of solar panels

Total energy output over lifetime

Cost per kilowatt-hour of the electricity.

co2 saved.

5.5 Green electricity from the grid

Cost per unit of electricity with and without.

co2 per unit of electricity.

5.6 Saving forests

Cost of buying a hectare of rain forest. Amount of carbon in the hectare of rain forest. What is the probability that, if you hadn’t bought it, it would have been cut down? Can we assume that the higher that probability is, the more valuable the land is, so choose a value along the upper part of the range? This does make some sense; using the value of the land as a proxy for the likelihood it will be used for other purposes. We could additionally use a value for this probability based on how fast the rain forest is disappearing.

Carbon in the hectare of rain forest, we may be able to assume that if the trees were cut down, there would be one meter of wood on the ground?

Need the carbon content of each kilo of organic material.

Mention very large benefits in terms of non-climate change environmental factors.

Look at TED talk about how this is one of the best methods.

There are also estimates of how much carbon each hectare of forest processes per year. This seems strange, because it doesn’t mention how much is released by bacteria or termites breaking down the dead wood. Maybe find out how accurate this estimate is. In case you want to look at this, then you can estimate the annual cost of a hectare of rainforest by doing a cost of house to rent conversion, and applying that to the cost of a hectare of forest.

5.7 Carbon credits

cost of carbon credits (also look for carbon offsets).

where do they come from? cap and trade?

are they any good?

Probably a complete fraud. But look at how they work, how much they cost per tonne of carbon.

5.8 Biofuels

I’m not sure what I meant. Wood burning? Corn ethanol? This is tough to quantify and may make sense to skip.

5.9 LED bulbs

Life of led bulb. Life of ordinary bulbs. Amount of energy used over life of led bulb. Energy used over life of ordinary bulbs. Difference in cost of bulbs, energy. Co2 expenditure.

5.10 House Insulation

Yay, we got some info on that. Also do your own calculations, starting from the average heating costs.