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Lecture 10

BIO220H1 Lecture Notes - Lecture 10: Numerical Weather Prediction, Lewis Fry Richardson, Svante Arrhenius


Department
Biology
Course Code
BIO220H1
Professor
John Stinchcombe
Lecture
10

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Lecture 10: Greenhouse gases & Climate Change
Climate changed a lot on earth
oHad shifts in biota
Entered 5th major ice age 2.5 MYA ago
Since then, cycling between more and less ice
Picture shows ice-free earth 55MYA
oSea levels high
An ice age has alternating glacial and interglacial periods
Over last ice age have alternating period of glacial and interglacial periods
oGlacial periods: Overall ice and glaciers expanding
oInterglacial periods: Ice and glaciers retreating
See estimates of air temperature taken from Vostock and EPICA ice core and from
sediment cores
As ice volume expands see real changes in temperature
For bottom graph (red), ice volume is low at top, and high in bottom
oSpike = decrease in ice volume = increasing temp
What’s next? Long-term predictions
Should enter glacial period soon:
oExit current interglacial in 10-50 thousand years
Glaciers return, Canada is toast
But next 100 years is what people are looking at
oWhat human activity has done that has altered what should happen
Four pioneers of climate prediction
Early workers of climate prediction in early 1800s
oJohn Tyndall
oSvante Arrhenius
oVihelm Bjerknes
oLewis Fry Richardson
Tyndall measured how different gases absorbed radiation
Discussed how water vapour can lead to GH effect
How water vapour really good at trapping heat in form of radiation and raises
temperature of things
Arrhenius calculated overall effects of CO2 as a greenhouse gas
Made prediction that doubling atmospheric CO2 concentrations should cause global
temperatures to increase 4C
Concluded that alternating glacial and interglacial periods were because of changing
atm CO2 that changed temperatures
Idea that increased coal burning (putting CO2 in atmosphere) was keeping next ice age
at bay

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His models about CO2 and climate change were rejected at a time
Arrhenuis was making these predictions long time ago
Globe slide
Bjerkes make primitive equations for modeling weather
Came up with differential predictions
Richardson used the equations to calculate the first numerical weather prediction
Used equations to make first weather prediction
Predicted the weather 6 ours in advanced
Did calculation by hand
Took 6 weeks
Noted that maybe in future can do these computations faster
ENIAC’s breakthrough predictions, 1950
One of first super computers that weighed 30 tons
Could predict weather 24hrs in advanced in 24 hours
From weather to climate
Ability to predict weather and climate has advanced tremendously w/ computing power
oComputing power made it possible to do this
People realized that local weather hard to predict
oComputational problems
oOverall chaotic problems with weather
But climate is predictable
oBecause climate is statistics of weather
oInstead of temperature tomorrow at noon, is the average temperature in Toronto
in February
oMore feasible
Can test models using predictions
oTake all info we know about climate and weather 10 years ago
oCompare past to records
Intergovernmental Panel on Climate Change
IPCC
Many different groups of scientists working on trying to predict climate independently
oTrying to understand what the signatures/tell-tale signs in data would be in
signs of climate change
Government: Who can we trust?
oSo established panel (IPCC) designed to prevent alarmist projections by
independent scientists
oPanel is supposed to identify the most robust results and most consistent
predictions
IPCC, continued
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Panel of scientists that would identify consensus
Collect all the data/reports from all the scientists and the panel goes through all the
research and identify the most robust and most consistent results
Charged with being neutral with respect to policy
Government says to panel, don’t tell us what to do, just tell us the state
So panel publish report every few years
Atmosphere + Earth Greenhouse Effect
The Greenhouse effect:
oSolar radiation coming in to Earth
Half of it is absorbed and warms earth
Some of it is reflected by clouds back into space, and some reflected by
surface
Can think of heat transfers (pools and fluxes)
oGH effect = consequence of radiation not making it back to space and warming
the earth
oAlbedo effect = reflection of heat back out into space
Overall temperature of earth is balance between these forces
oOne protecting planet from warming (reflection) one warming planet
Albedo (= reflectivity) important to earth’s energy balance
What happens to radiation coming into earth?
Snow is white so reflects ~75% back to earth
As temperature warms up, snow cover decreases (especially in oceanic areas) so more
exposed water
oFeedback where earth warms, snow melts, more exposed water, water absorbs
more energy and warms climate around it
oLeads to more snow melt
Past climate cooling is sometimes reflected by mountain ranges covered with snow and
reflect heat to space
Charles Keeling measured CO2 at Mauna Loa, Hawaii
Studied atm concentrations of CO2
Saw that CO2 drops in concentration in summer months
oBecause of photosynthesis pulling it out
oAt end of growing season, leaves fall, plants die, decomposition, and CO2 goes
back up
So have annual cycle
Keeling first interested in annual cycle, but soon perceived upward trend
Started in 60s and 70s
At first only interested in the annual cycles (previous slide)
Then start to find that overall concentration CO2 was going up and up
BIO220 and global CO2 in real time
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