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Lecture 9

EESA01 Lecture 9: lecture 9 enviro sci


Department
Environmental Science
Course Code
EESA01H3
Professor
Carl Mitchell
Lecture
9

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Eess - lecture 9 - global climate change
Debunking climate sceptics
- Milankovitch factors
- precession - slow change of axis of earth rotation
- takes about 22 000 years
- obliquity - subtle change of the actual angle of the axial tilt from 22.1 to 24.5
degrees
- occurs over about 41 000 years
- eccentricity - shape of earth orbit changes from nearly circular to more egg shaped
- over 100 000 years
- This results in earth going in and out of glacial period = ice age
The greenhouse e'ect
- Water vapour is most important
greenhouse gas in the
atmosphere
- The amount of energy that is
stored should be the
same as the amount that is
taken in
What we know - greenhouse gases
- Most greenhouse gases are both
naturally and human-generated
- Important ones - have the
strongest radiating forces --
CO2, methane and nitrous oxide
- Human activities have increased
GHG emissions over past 300
years
- This has enhanced the Greenhouse E'ect
- Di'erent gases have di'erent global warming potentials
- this is radiating forces
- number given that is relative to the ability of CO2 to function as s greenhouse gas
- CO2 has global warming potential of 1
- methane is 25 - so every molecule of methane has 25 time the ability to warm the
earth than every molecule of CO2
- really potent
- good thing it is at a really low concentration on earth
- methane is from cow manure, farts
- nitrous oxide is 298 GWP
- big agricultural pollutant
- Carbon dioxide
- measured in ppm
- Methane and nitrous oxide is in ppb

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Sources of C02
- The decay of organic matter (respiration; decomposition)
- Breathing
- Burning anything carbon-based
- Volcanic eruptions
- Natural sources outweigh anthropogenic sources, but it is human activity that has
increased the overall pool of CO2 in the atmosphere à removal from lithosphere and into
atmosphere (shifted :uxes
- Increase from 280 ppm in 1700’s to ~400 ppm today
The carbon budget
- Process of photosynthesis and
respiration are more or less
equal , but there is stu' like
industry, changing land use,
transportation that are
increasing how much CO2 is going
into the atmosphere and those
natural processes cannot keep up
- We are throwing more into the
atmosphere than we can
reabsorb
- When CO2 goes into the water, it
becomes more acidic
Calculation example
How many kg of CO2 are emitted from the average car driving to this campus from Markham?
Let’s say you drive a Volvo sedan
According to some websites I found, a Volvo sedan emits an average of 217 g CO2 km-1
From downtown Markham to this campus is about 27 km
217 g CO2 km-1 x 27 km = 5859 g = 5.9 kg
This is ONE WAY
How much would a tree in your yard have to grow to sequester that much CO2?
Presume wood density of 700 kg m-3, that the tree has a diameter of 20 cm, that tree gains mass
only by growing UP, that it is round, and that it is 100% carbon
700 kg m-3 = 7 x 10-4 kg cm-3
With diameter = 20 cm, area = πr2 = 300 cm2
So, each cm height of trunk is ~ 7 x 10-4 kg cm-3 x 300 cm2 = .2 kg cm-1
So, to replace 5.9 kg, the tree would need to grow ~30 cm
How many 20 cm diameter trees that grow 30 cm d-1 do you have in your yard (BTW, trip to
Markham only 1-way)
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