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Lecture 11

EESA09H3 Lecture 11: chapter 11 notes


Department
Environmental Science
Course Code
EESA09H3
Professor
Tanzina Mohsin
Lecture
11

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Lecture 11 weather vs climate
Weather:
What is it like outside? (talking about now, no location or time
specified)
Short term phenomena
Climate:
What is it usually like outside? (specify location and season)
A description of typical weather conditions for a location and
time of year
Use weather data to define climate
Based on statistics accumulated over a long period of time (at
least 30 years)
30 years of climate change is called climate normal
Toroto’s climate for July
30 years of data from
Environment Canada
Tmean = 22.2C
Tmax = 26.4C
Tmin = 17.9C
Rain: 67.5 mm
Extreme Tmax: 40.6C
Extreme Tmin: 3.9C
Extreme daily rain: 98.6
Mm
Factors that influence local climate
1. Latitude
- Incident radiation from the sun
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2. Global circulation
- Prevailing wind (easterlies) , jet streams, ocean currents
3. Air masses
- Transport of warm or cold moist or dry air
(North America cT , mT, Ct , MT)
4. Geography
- Eg, rainshadows from mountains , land/sea breeze
5. Land cover
- Albedo, evaporation, heat capacity
What is a feedback?
Two types:
1. positive
2. negative
Positive
A hage i A ill ause a hage i B, which in turn will cause a
hage i A i the same direction is called a positive feedback.
Negative
Hoeer, if a hage i A ause a hage i B ad that will cause
i A i the opposite direction then it is a negative feedback
1. Albedo (ice-snow feedback)
What is albedo?
Reflectivity of surface (how much radiation it can reflect)
- Change in albedo will change the local climate
- Large scale albedo changes can affect the global climate
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- Feedback: climate change can cause changes in cloud and snow
cover, which in turns further climatic change
-
What kind of feedback? Positive feedback
Explaination: when there is warm climate, there is less ice and snow,
less reflectivity, more warming, more melting (positive feedback
cycle)
(study from leture notes)
2. Clouds
What kind of feedback? negative feedback
Whe it is refletig the su’s radiatio fro the top toards the
space, it cause cooling effect which is negative feedback
History climate change
1. Volcanic eruptions
- Co2 emitted
- Dust and sulfuric acid particles launched into the stratosphere
- These aerosols remain in the air for several years
- 1816 year ithout suer (aerosols stay in atmosphere
ad reflet su’s radiatio ko as aerosol egatie feedak
- Massive eruptions in 1812 (St. Vincent), 1814 (Philippines) and
1815 (Indonesia)
- Major June snowstorms in North America in 1816
- Crop failure and starvation across the northern hemisphere
2. Solar variation
- Long term cycles in solar characteristic have been observed
- The Mauder Miiu i 1th century
- Coiided ith the little ie age
- It is still cant be proved whether low temperatures were caused
by the decrease in solar strength
3. Milankovic theory and ice ages
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