Chapter 1 Earth System and Climate system 1

Chapter 1: Earth System and Climate system 1

The Habitable Earth The earth is the only habitable planet in our solar system. Oceans: 70% of the surface Land: 30% Earth’s climate is favorable to life. In the era of population explosion, climate change is critical to human life. 2

We will discuss: 1. What are the components of Earth system, especially Earth’s climate system? 2. How does climate change differ from day-to-day weather? 3. Climate Classification 4. What factors drive changes in Earth’s climate? 5. How does the climate system work? 6. 3

Earth system composed of 4 interacting parts driven by solar energy: • Atmosphere • Hydrosphere • Solid earth • Biota 4

Schematic diagram of the Earth system, showing interactions among its four components. 5

Weather versus Climate Weather The condition of atmosphere at a given time and place v Short-term (and large) fluctuations that arise from internal instabilities of the atmosphere v Occurs as a wide variety of phenomena that we often experience v Effects are immediately felt v Social and economic impacts are great but are usually localized v Governed by non-linear chaotic dynamics; not predictable deterministically beyond a week or two 6

Low Pressure Cyclonic Turning: Convergence leads to upward vertical motions. High Pressure Anti-Cyclonic Turning: divergence leads to downward vertical motions. Cold Air Warm Air 7

Impacts of Weather Figure 1. 15 8

Impacts of Weather 9

Hurricane: Gustav in New Orleans. 2 Million people evacuated (Sep. 1, 2008) 10

Climate versus Weather Climate v Defined as the average state of the atmosphere over a finite time period and over a geographic region (space). v Can be thought of as the “prevailing” weather, which includes the mean but also the range of variations v The wide range of natural variability associated with daily weather means small climate changes are difficult to detect v Intimate link between weather and climate provides a basis for understanding how weather events might change under a changing climate v Involves atmospheric interactions with other parts of the climate system and external forcing v Climate prediction is complicated by considering the complex interactions between, as well as changes within, all components. 11

• Climate is typically described by the statistics of a set of atmospheric and surface variables, such as temperature, precipitation, wind, humidity, cloudiness, soil moisture, sea surface temperature, and the concentration and thickness of sea ice. • The statistics may be in terms of the long-term average, as well as other measures such as daily minimum temperature, length of the growing season, or frequency of floods. • Although climate and climate change are usually presented in global mean terms, there may be large local and regional departures from these global means. These can either mitigate or exaggerate the impact of climate change in different parts of the world. 12

v Climate is what you expect and weather is what you get. v Climate tells what clothes to buy, but weather tells you what clothes to wear. 13

Review Questions Which of the following statements relate more to weather (A) and which relate more to climate (B)? 1. The summers in Prince George are cool and dry. 2. It is 30°C right now, partly sunny, and south winds 10 to 20 miles per hour. 3. September 2001 was the 2 nd coolest September of record for Prince George International Airport. 4. The pressure now is 29. 75 inches and steady, and humidity is 84%. 14

Review Questions Which of the following statements relate more to weather (A) and which relate more to climate (B)? 1. The summers in Prince George are cool and dry. (B) 2. It is 30°C right now, partly sunny, and south winds 10 to 20 miles per hour. (A) 3. September 2001 was the 2 nd coolest September of record for Prince George International Airport. (B) 4. The pressure now is 29. 75 inches and steady, and humidity is 84% (A). 15

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Koppen's Worldwide Distribution of Climatic Regions II 17

A: Tropical moist • Tropical wet (Af) • Tropical moonsoon (Am) • Tropical wet and dry (Aw) 18

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B: Dry Climate • • Arid (BW) – the “true desert”: Semi-arid (BS): 25

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C: Moderate Climate • Humid sybtropical (Cfa): • Marine (Cfb): • Dry-summer subtropical (also referred to as Mediterrannean) (Cs): 28

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D: Continental Climate • humid continental with hot summer (Dfa) • humid continental with cold summer (Dfb) • subplot (Dfc) 31

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E: Polar Climate • Tundra climate • Ice Cap climate 35

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Koppen's Worldwide Distribution of Climatic Regions II 40

Earth History Earth’s age: 4. 55 billion years (Byr) = 4, 550, 000 years = 4. 55 × 109 years This course focuses on only recent 10% of its age. 41

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. 42

Development of Climate Science 19 th century – early 20 th century: isolated studies. Middle 20 th century – 1980 s: rapid development into a mature science. In the past two decades: earth system approach. Multidisciplinary & interdisciplinary. “Your tools are terribly antiquated and imprecise” Climate Modeler How scientists study climate change: Observations Theory “You produce junk and waste a lot of money” Field-Geologist 43

• How scientists study climate changes (1) spend much time to gather and analyze data from the kind of climatic archives. To publish results in peer-reviewed journals. (2) need to explain and interpret results – Hypothesis, theory. (3) Models (4) Charles Darwin: Evolution Plate tectonics It is time to expect a new revolution in knowledge of Earth history. 44

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, … 45

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 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. 46

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The Climate System Components 48

• Climate Forcing: can be defined as an imposed perturbation of Earth’s energy balance. (1) natural forcing: luminosity of the sun; volcanic eruption; earth’s orbit (2) Anthropogenic forcing (fossil fuel burning) – ( greenhouse gases forcing (unit: ) changes in global temperature. Climate Sensitivity 49

Forcing and Response: A Bunsen Burner Experiment Three major kinds of climate forcing in nature: üTectonic processes üEarth-orbital changes üChanges in Sun’s strength Flame is far enough away üAnthropogenic forcing üUrbanization üDeforestation üBurning fossil fuels üAgriculture Response time depends on “materials” or “components”. 50

Climate: An Engineer’s View Anthropogenic forcing Machine Output Input 51

• Climate sensitivity: The sensitivity of the climate systems to a forcing is commonly expressed in terms of the global mean temperature changes that would be expected after a time sufficiently long for both the atmosphere and ocean to come to equilibrium with the change in climate forcing. An important factor of climate sensitivity is feedback of components of the climate system. An example: if CO 2 concentration doubles (forcing 4 w/m^2), the temperature will increase 1. 2 C if no feedback. However, the situation is very complicated due to feedbacks. For example, CO 2 up => T up => ice melting => surface color changes => more sun lights absorbed => T up…. feedbacks cause uncertainty in climate changes. . 52

Response Times of Various Climate System Components 53

Feedbacks 54

Feedbacks 55

Water Vapor Feedback 56

warming Decreased snow and ice; less reflectivity More solar radiation absorbed at surface Ice-Albedo Feedback 57

Initial Change Climate warming Reduced Warming Uncertain Increased clouds Greater reflected radiation Cloud Radiative Feedbacks 58

FEEDBACKS INVOLVED IN GLOBAL WARMING 59

CLIMATE SENSITIVITY 60

CLIMATE SENSITIVITY 61

CLIMATE SENSITIVITY The ‘commitment’ to future warming 62