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

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

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

Impacts of Weather

Impacts of Weather

Impacts of Weather

Impacts of Weather

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.

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

Koppen's Worldwide Distribution of Climatic Regions, I

Koppen's Worldwide Distribution of Climatic Regions, II

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 29.75 inches and steady, and humidity is 84%.

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 29.75 inches and steady, and humidity is 84%.

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

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

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

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, …

The Climate System Components

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.

Climate: An Engineer’s View Input Machine Output

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”.

Response Times of Various Climate System Components