What is your carbon footprint?
David Willms, Professional Engineer and environmentalist
Northern Digital Inc.
Waterloo ON N2V 1C5
Lew Brubacher, retired prof and environmentalist
Department of Chemistry, University of Waterloo
Waterloo ON N2L 3G1
One’s personal carbon footprint can be viewed as a measure of
the carbon dioxide (CO2) emitted through the burning of fossil
fuels, either directly or indirectly, as part of one’s daily life.1
CO2 is one of the greenhouse gases, along with methane, water
vapour and some other gases. Atmospheric levels of CO2 have
cycled between about 180 ppm and 290 ppm over the past
400,000 years (Fig. 1). However, over the past 150 years,
levels have risen to 380 ppm (Fig. 2), a 30% increase over
previous highs. It is universally accepted that this dramatic
increase is the result of human activity, and the vast majority of
atmospheric scientists agree that this is a major cause of global
warming.2,3
2. Air travel – how far you fly, what type of plane and how full
the flight is.
3. Home heating – your fuel use and type (electricity, natural
gas or oil)
4. Home electricity – depends on where your electricity comes
from and how much you use.
5. Food and things – how much fossil fuel was used to produce
and deliver the food we eat and make the products we buy.
6. Industry – CO2 emitted by our employers, public institutions,
businesses, etc., on our behalf.
We’ll tackle the first four items on the list, an approach taken by
many of the carbon calculators found online.5 This is not to
underestimate the impact of the food we eat and places we work
— they’re just more difficult to quantify from person to person.
Now is when a spreadsheet comes in handy.
Car. Determine how far you drove last year, or divide your
odometer reading by the number of years you’ve owned your
car. Next, find your car’s fuel economy in litres per 100 km6 (in
Canada). Readers in the U.S. can find fuel economy numbers in
miles per gallon,7 then convert miles travelled to kilometres and
miles per gallon to L/(100 km). Take the simple average of the
city and highway consumption for your vehicle unless you know
what the actual proportions are for your case. Let’s say that you
drove 20,000 km last year in a 1999 Toyota Corolla (average
fuel consumption, 7.7 L/100 km).6 You would have emitted
20,000 km ×
Fig. 1. Variation of CO2 concentration (middle curve, in parts
per million) and temperature (upper curve), based on ice
core data from Antarctica, over the past 400,000 years.4
Fig. 2. Carbon dioxide levels, 1958-2006.
How much CO2 do you or I contribute in a year? There are
online carbon footprint calculators, but we’ll develop our own.
A few key sources make up the bulk of the average CO2 footprint:
1. Car – how much fuel you use (efficiency and distance) and
how many passengers share the ride.
16 Chem 13 News/November 2007
2.1 kg CO 2
1t
7 .7 L
×
×
= 3.2 t CO 2 8 (eq 1)
1000 kg
100 km
L
(See Note 1 below for the origin of the 2.1 factor.) Of course, if
you had a passenger with you the whole time, you would share
the CO2 between the two of you, giving 1.6 t each. If you had
driven a 2006 Hummer H3 instead, you would have run up a
5.7-t CO2 bill. On the other hand, by biking to work for the past
five years, one of us (DW) has saved 2 t of CO2.
Air Travel. Record the number of flights you made last year
and determine the total distance travelled9 including return
flights. Because take-off and landing uses significantly more
fuel, layovers and transfers count as separate flights. Similar to
car travel, the CO2 emitted per km depends on the efficiency of
the airplane and how many people share the flight. Here, we’ve
assumed a 747 at 80% occupancy. The factors in the following
formula were taken from the internet. Your CO2 tonnage is:
[Number of flights this year x 0.0551 t CO2/flight]
+ [Distance travelled (in km) x 0.000101 t CO2/km]
= mass CO2 (in tonnes)10
(eq 2)
The factor 0.000101 t CO2/km in this equation corresponds to a
consumption of 4.8 L/(100 km),11 if we assume, as a reasonable
approximation, that Note 1 applies here as well. As an example,
suppose you fly from Toronto to Calgary and back, and that the
plane touches down at Winnipeg going out but the return flight is
direct. This amounts to three flights. The distance is 1,514 km
(Toronto to Winnipeg) plus 1,204 km (Winnipeg to Calgary), then
2,711 km on the return (Calgary to Toronto), a total of 5,429 km
distance travelled. The calculation is (3 x 0.0551) + (5,429 x
0.000101) = 0.71 t CO2. Your travelling partner would also have
a 0.71-t CO2 footprint.
Canada’s target under Kyoto is 14 t per year per person, well
above the world average of 4 t per year per person. Globally,
we all need to lower our emissions to 2 t or less in order to
stabilize CO2 in the atmosphere.15 Clearly, we in Canada and
the United States contribute more than our fair share and have
an obligation to take steps to reduce our output in the fight
against global warming.
Notes
As a rule of thumb, one plane emits about as much CO2 as would
every passenger driving one car the same distance. The full
story of air travel is actually more complicated than this.
Airplanes also emit tonnes of water vapour and nitrous oxides at
high altitudes, which may have a warming effect equivalent to
three times the CO2 emitted! This effect is not yet well
understood, so we haven’t included it here.
Home Electricity. In Ontario, only 24% of our electricity comes
from CO2-producing processes — natural gas, oil and coal-fired
power plants.12 “Cleaner”13 hydro and nuclear make up the
other 76%.12 The calculation is easy, but you do need last
year’s electricity bills. Your CO2 tonnage from electricity use is:
1. To calculate the CO2 release in burning gasoline, assume
that the gasoline is pure isooctane (C8H18; M, 114.2; density,
0.692 g/mL), one of its components. The reaction is
C8H18 + 12.5 O2 → 8 CO2 + 9 H2O
Thus, 1 L of isooctane, 692 g, is 6.06 mol and produces
48.5 mol CO2 or 2.13 kg CO2. This is the factor that was
used in eq 1, 2.1 kg CO2/(L gasoline). You can ask your
students to do similar calculations for other hydrocarbons.
2. Natural gas is mainly methane, CH4, plus small amounts of
ethane and heavier hydrocarbons. It burns according to
CH4 + 2 O2 → CO2 + 2 H2O
Natural gas volumes are measured at 15oC and
approximately 1 atm pressure, so 1 m3 contains
Total electricity used (in kW h) x 0.0010 t/(kW h) x 0.24
= mass CO2 (in tonnes) (eq 3)
n=
To determine your personal contribution, divide this CO2 tonnage
by the number of people who share your home. In jurisdictions
other than Ontario, find the website of your electricity provider in
order to ascertain the percentage of your electricity produced by
burning fossil fuels. Use that percentage, as a fraction, in place
of the 0.24 factor in eq 3.
Home Heating. If you heat with electricity, you’re already done!
Most of us, however, heat our homes and maybe water with
natural gas. Have a look at the past year’s bills and total the
gas used, in cubic metres. Your home’s CO2 contribution is:
Total gas used (in
m3)
x 0.0020
t/m3
= mass CO2
(eq 4)
(See Note 2 for the origin of the 0.0020 factor in this equation.)
As with electricity, divide this by the number of people in the
home — everyone claims their share of CO2.
Summing up. Totalling the CO2 from all of these sources
should give you a reasonable estimate of your yearly
contribution. If you have calculated for your whole household,
divide by the number of people in your home to get your
personal carbon footprint. How did you do? One of the authors
(LB), who lives in a well insulated townhouse with his wife, had a
personal carbon footprint of 6.0 t in 2006. But this does not
include CO2 from sources 5 and 6 in our starting list, sources
that might double or even triple our per capita amount.
The average per capita, annual emission is 20.0 t in Canada
and 20.4 t in the United States (2004 data).14 (These values are
estimated by dividing the country’s population into the CO2
output from the total amount of fossil fuels used by that country,
and includes all sources.) This is nearly four times the Swiss
average and more than five times the Chinese average.
PV
1 atm × 1m 3 × 1000 L m -3
=
= 42.3 mol
RT 0.0821L atm mol -1 K -1 × 288 K
Accordingly, 1 m3 of natural gas produces 42.3 mol of CO2,
or 1.86 kg. Since 1 mol of ethane produces 2 mol CO2, 1 m3
of ethane produces twice as much CO2, or 3.72 kg. For
natural gas that is, say, 95% methane and 5% ethane, the
weighted average is 1.95 kg CO2/(m3 natural gas), or
approximately 0.0020 t/m3, the factor used in eq 4. Ask your
students to calculate the factor for other proportions.
References
1. For a more careful definition, see
http://en.wikipedia.org/wiki/Carbon_footprint.
2. http://en.wikipedia.org/wiki/Greenhouse_gas
3. http://www.davidsuzuki.org/Climate_Change/Science/IPCC; or
Intergovernmental Panel on Climate Change, see http://I pccwg1.ucar.edu/wg1/Report/AR4WG1_Print_SPM.pdf
4. http://en.wikipedia.org/wiki/Image:Vostok-ice-core-petit.png.
5. http://summits.ncat.org/carbon_calcs.php
6. http://oee.nrcan.gc.ca/transportation/tools/fuelratings/rating ssearch.cfm?attr=8
7. https://www.fueleconomy.gov/mpg/MPG.do?action=addGue
stVehicle
8. These are metric tonnes, 1 t = 1000 kg.
9. http://www.travelhappy.co.uk/mytrip/
10. http://www.chooseclimate.org/flying/mf.html
11. http://en.wikipedia.org/wiki/Fuel_efficiency_in_transportation
12. http://www.opg.com/power/
13. http://www.dams.org/news_events/press333.htm
14.
http://en.wikipedia.org/wiki/List_of_countries_by_carbon_dioxide_
emissions_per_capita
15. http://www.manicore.com/anglais/documentation_a/green
∎
house/quota_GHG.html
November 2007/Chem 13 News 17