1. Lecture 2: Weather and Climate
Ch. 1 (p.1-16)
Weather and climate
Earth history
Time scales of climate change
Development of climate science
Components of the climate system
Forcing and response
Response times

2. Weather versus Climate
The condition of atmosphere at a given time and place
Short-term (and large) fluctuations that arise from internal instabilities
of the atmosphere
Occurs as a wide variety of phenomena that we often experience
Effects are immediately felt
Social and economic impacts are great but are usually localized
Many such phenomena occur as part of larger-scale organized systems
Governed by non-linear chaotic dynamics; not predictable
deterministically beyond a week or two

3. Low Pressure High Pressure
Anti-Cyclonic
Turning:
divergence
leads to downward
vertical motions.
Cyclonic Turning:
Convergence
leads to upward
vertical motions.
Cold Air
Warm Air

4. Impacts of Weather

5. Impacts of Weather

6. Impacts of Weather

7. Impacts of Weather

8. Weather versus Climate Climate
Defined as the average state of the atmosphere over a finite time
period and over a geographic region (space).
Can be thought of as the “prevailing” weather, which includes the
mean but also the range of variations
The wide range of natural variability associated with daily weather
means small climate changes are difficult to detect
Intimate link between weather and climate provides a basis for
understanding how weather events might change under a
changing climate
Climate is what you expect and weather is what you get.
Climate tells what clothes to buy, but weather tells you what clothes to wear.

9. Climate versus Weather
Defined as the average state of the atmosphere over a finite time
period and over a geographic region (space).
Can be thought of as the “prevailing” weather, which includes the
mean but also the range of variations
The wide range of natural variability associated with daily weather
means small climate changes are difficult to detect
Intimate link between weather and climate provides a basis for
understanding how weather events might change under a
changing climate
Involves atmospheric interactions with other parts of the climate
system and external forcing
Climate prediction is complicated by considering the complex
interactions between, as well as changes within, all components

10. Koppen's Worldwide Distribution of Climatic Regions, I

11. Koppen's Worldwide Distribution of Climatic Regions, II

12. Review Questions
Which of the following statements relate more to weather (A) and which relate more to climate (B)?
1. The summers in Austin are hot and humid.
2. It is 75°F right now, partly sunny, and south winds 10 to 20 miles per hour.
3. September 2001 was the 2nd coolest September of record for Austin/Bergstrom International Airport.
4. Although winters in Austin are on the average mild by U.S. standards, cold outbreaks sometimes come, in some years more frequent than in others. These cold outbreaks are sometimes preceded or followed by periods of summerlike weather.
5. The pressure now is inches and steady, and humidity is 84%.

13. Review Questions
Which of the following statements relate more to weather (A) and which relate more to climate (B)?
B 1. The summers in Austin are hot and humid.
A 2. It is 75°F right now, partly sunny, and south winds 10 to 20 miles per hour.
B 3. September 2001 was the 2nd coolest September of record for Austin/Bergstrom International Airport.
B 4. Although winters in Austin are on the average mild by U.S. standards, cold outbreaks sometimes come, in some years more frequent than in others. These cold outbreaks are sometimes preceded or followed by periods of summerlike weather.
A 5. The pressure now is inches and steady, and humidity is 84%.

14. Earth History Earth’s age: 4.55 billion years (Byr)
This book focuses on only recent 10% of its age.

15. Time Scales of Climate Change
Earth’s climate changes all the time, e.g., last 300 Myr, last 3 Myr, last 50,000 yr, and last 1000 yr.
Hockey Stick

16. Development of Climate Science
19th century – early 20th century: isolated studies.
Middle 20th century – 1980s: rapid development into a mature science.
In the past two decades: earth system approach.
Multidisciplinary & interdisciplinary.
How scientists study climate change:
Observations  Theory
“Your tools are terribly antiquated and imprecise”
“You produce junk and waste a lot of money”
Climate Modeler
Field-Geologist

17. Components of the Climate System
Five major components: air (atmosphere), water (hydrosphere), ice (cryosphere), vegetation (biosphere), and land (lithosphere).
Major processes: energy cycle, water cycle, carbon cycle, …

18. The Climate System Components

19. Climate System Components
Atmosphere
Fastest changing and most responsive component
Previously considered the only “changing” component
Ocean
The other fluid component covering ~70% of the surface
Plays a central role through its motions and heat capacity
Interacts with the atmosphere on days to thousands of years
Cryosphere
Includes land snow, sea ice, ice sheets, and mountain glaciers
Largest reservoir of fresh water
High reflectivity and low thermal conductivity
Land and its biomass
Slowly changing extent and position of continents
Faster changing characteristics of lakes, streams, soil moisture
and vegetation
Human interaction
agriculture, urbanization, industry, pollution, etc.

20. Climate: An Engineer’s View
Input
Machine
Output

21. Forcing and Response: A Bunsen Burner Experiment
Three major kinds of climate forcing in nature:
Tectonic processes
Earth-orbital changes
Changes in Sun’s strength
Anthropogenic forcing
Urbanization
Deforestation
Burning fossil fuels
Agriculture
Response time depends on “materials” or “components”.

22. Response Times of Various Climate System Components