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Lecture 10

BIO220H1 Lecture 10: Lecture10_2015_6.pdf


Department
Biology
Course Code
BIO220H1
Professor
Nicole Mideo
Lecture
10

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2/4/2015
1
Lecture 10:
Greenhouse gases & climate change
Earth has seen many
changes in climate,
accompanied by drastic
shifts in biota
Entered 5
th
major “ice
age” about 2.58 MYA
Since then, cycling
between more and less
ice
Ice-free
Earth,
55 MYA,
sea levels high
Nat Geog
An ice age has alternating glacial and
interglacial periods
Estimates from
ice cores
From sediment
cores
What’s next? Long-term predictions:
Exit the current
interglacial in 10 to
50 thousand yr
Glaciers return, sea
level drops, Canada is
toast
But the short-term
prediction is very
different, due to
human activity
T. Crowley
Four pioneers of climate prediction
John Tyndall (1820-1893)
Svante Arrhenius (1859-1927)
Vilhelm Bjerknes (1862-1951)
Lewis Fry Richardson (1881-1953)
Tyndall measured how different gases
absorbed radiation
Discussed greenhouse effect
of water vapour
Arrhenius calculated overall effects of CO
2
as a greenhouse gas
Doubling of atmospheric [CO
2
] should cause global
temperature to increase 4 C
Concluded that alternating glacial and interglacial
periods were due to this
Felt that increased coal burning was fending off the
next ice age
Contemporaries rejected his CO
2
-climate
connection in favour of Milankovich cycles, but now
both are thought to be important
Newer models confirm his 4 C prediction

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2/4/2015
2
Bjerknes wrote the “primitive equations”
for a model of weather including air
movements, temperature, and water content.
Six coupled differential equations, calculations
overwhelming!
Richardson used the equations to calculate the first
numerical weather prediction
Predicted weather for
6 hours
Calculations took him
6 weeks
Perhaps some day in the
dim future it will be
possible to advance the
computations faster than
the weather
advances…But that is a
dream.
ENIAC’s breakthrough prediction, 1950
Weighed 30 tons
>17,000 vacuum tubes
5 million solder joints
Predicted
24 hrs of
weather in
24 hrs!
From weather to climate
Can’t predict local weather far in advance
because of its chaotic nature (and
estimation/computing limitations)…
…but climate = the statistics of weather, whi ch is
in fact predictable.
How can predictive ability be assessed when the
future is unknown?
Apply backward “prediction,compare to past
records
Intergovernmental Panel on Climate Change
Different groups working in various countries on:
Model building
Collecting data on past climates
Validation & “signatures” of causes
Governments: Whom can we trust?
IPCC established 1988 by United Nations
Designed to avert “alarmist” projections by independent
scientists; inherently conservative and slow procedural
structures
IPCC, continued
IPCC does not conduct research; it provides protocols &
reviews to assess which results are most robust,
consistent, and best supported by data; neutral with
respect to policy
Reports based on peer-reviewed literature
Published 4
th
assessment, 2007
5
th
assessment in progress, publication in 2014
IPCC (including Bob Jefferies) shared 2007 Nobel Peace
Prize
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13
is
IPCC, 2007
These energy transfers
much affected by albedo
& greenhouse effects
Albedo (= reflectivity) important to earth’s
energy balance
Fresh snow reflects ~ 75%
Crops ~ 20%
Forest ~ 10%
Water ~5%
Past climate cooling associated with uplift of
mountain ranges and creation of new snowy
regions
Charles Keeling (1928-2005): measured [CO
2
] at
Mauna Loa, Hawaii
Atmospheric
concentration
of CO
2
Drops because
taken up by
photosynthesis
during northern
summer
Recovers during
northern winter
Keeling first interested in annual cycle, but soon
perceived upward trend
Bio220 and global C02 in real time
Data from NOAA
Jan2005:378.76
Jan2012:393.12
Jan2013:395.54
Jan2014:397.80
Jan252015:400.18
18
Increases in CO2concentration at
different sites worldwide
American Samoa
Barrow, Alaska Mauna Loa, Hawaii
South Pole
14º S 90º S
19º N71º N
Atmospheric CO
2
concentration
(ppm)
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