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Chapter 1:

Earth System and Climate system

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The Habitable EarthThe Habitable EarthThe earth is the only habitable planet in our solar system.The earth is the only habitable planet in our solar system.

Oceans: 70% of the surfaceOceans: 70% of the surfaceLand: 30%Land: 30%

Earth’s climate is favorable to life.Earth’s climate is favorable to life.

In the era of population explosion, climate change is In the era of population explosion, climate change is critical to human life. critical to human life.

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We will discuss:We will discuss:

1.1. What are the components of Earth system, especially What are the components of Earth system, especially Earth’s climate system?Earth’s climate system?

2.2. How does climate change differ from day-to-day How does climate change differ from day-to-day weather? weather?

3.3. Climate Classification Climate Classification

4.4. What factors drive changes in Earth’s climate?What factors drive changes in Earth’s climate?

5.5. How does the climate system work?How does the climate system work?

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Earth system

composed of 4 interacting parts driven by solar energy:

•Atmosphere

•Hydrosphere

•Solid earth

•Biota

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

components.

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Weather versus Climate

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

Governed by non-linear chaotic dynamics; not predictable deterministically beyond a week or two

The condition of atmosphere at a given time and placeWeather

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Low Pressure High Pressure

Cyclonic Turning:

Convergence

leads to upward

vertical motions.

Anti-Cyclonic

Turning:

divergence

leads to downward

vertical motions.

Cold Air

Warm Air

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Impacts of WeatherImpacts of Weather

Figure 1.15Figure 1.15

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Impacts of WeatherImpacts of Weather

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

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ClimateClimate versus Weather

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.

Defined as the average state of the atmosphere over a finite time period and over a geographic region (space).

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• 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.

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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.

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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 2nd coolest September of record for Prince George International Airport.

4. The pressure now is 29.75 inches and steady, and humidity is 84%.

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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 2nd 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).

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Koppen's Worldwide Distribution of Climatic Regions IIKoppen's Worldwide Distribution of Climatic Regions II

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A: Tropical moist

• Tropical wet (Af)

• Tropical moonsoon (Am)

• Tropical wet and dry (Aw)

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B: Dry Climate

• Arid (BW) – the “true desert”:

• Semi-arid (BS):

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C: Moderate Climate

• Humid sybtropical (Cfa):

• Marine (Cfb):

• Dry-summer subtropical (also referred to as Mediterrannean) (Cs):

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D: Continental Climate

• humid continental with hot summer (Dfa)

• humid continental with cold summer (Dfb)

• subplot (Dfc)

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E: Polar Climate

• Tundra climate

• Ice Cap climate

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Koppen's Worldwide Distribution of Climatic Regions IIKoppen's Worldwide Distribution of Climatic Regions II

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Earth HistoryEarth History

Earth’s age:Earth’s age:

4.55 billion years 4.55 billion years (Byr) (Byr)

= 4,550,000,000 = 4,550,000,000 yearsyears

= 4.55 = 4.55 × 10× 1099 years years

This course This course focuses on only focuses on only recent 10% of its recent 10% of its age.age.

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Time Scales of Climate ChangeTime Scales of Climate Change

Earth’s climate changes all the time, e.g., last 300 Earth’s climate changes all the time, e.g., last 300 Myr, last 3 Myr, last 50,000 yr, and Myr, last 3 Myr, last 50,000 yr, and last 1000 yr..

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Development of Climate ScienceDevelopment of Climate Science

Climate Modeler Field-Geologist

1919thth century – early 20 century – early 20thth century: century: isolated studies.isolated studies.

Middle 20Middle 20thth century – 1980s: rapid century – 1980s: rapid development into a mature science. development into a mature science.

In the past two decades: earth system In the past two decades: earth system approach.approach.

Multidisciplinary & interdisciplinary. Multidisciplinary & interdisciplinary.

“Your tools are terribly antiquated

and imprecise”

“You produce

junk and waste a lot of money”

How scientists study climate change:How scientists study climate change:

Observations Observations Theory Theory

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• 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.

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Components of the Climate SystemComponents of the Climate System

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

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Climate System ComponentsAtmosphere• 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.

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The Climate System Components

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• 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 (Anthropogenic forcing (fossil fuel burning) – greenhouse gases forcing (unit: ) changes in global temperature.

Climate Sensitivity

2mw /

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Forcing and Response: A Bunsen Burner ExperimentForcing and Response: A Bunsen Burner Experiment

Three major kinds of Three major kinds of climate forcing in climate forcing in nature:nature:Tectonic processesTectonic processesEarth-orbital changesEarth-orbital changesChanges in Sun’s strengthChanges in Sun’s strength

Anthropogenic forcingAnthropogenic forcingUrbanizationUrbanizationDeforestationDeforestationBurning fossil fuelsBurning fossil fuelsAgricultureAgriculture

Response time depends Response time depends on “materials” or on “materials” or “components”.“components”.

Flame is far enough awayFlame is far enough away

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Climate: An Engineer’s ViewClimate: An Engineer’s View

InputInput

MachineMachineOutputOutput

Anthropogenic Anthropogenic forcingforcing

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• 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 CO2

concentration doubles (forcing 4w/m^2), the temperature will increase 1.2C if no feedback. However, the situation is very complicated due to feedbacks. For example, CO2 up => T up => ice melting => surface color changes => more sun lights absorbed => T up….

feedbacks cause uncertainty in climate changes..

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Response Times of Various Climate System ComponentsResponse Times of Various Climate System Components

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Feedbacks

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Feedbacks

56Water Vapor Feedback

57Ice-Albedo Feedback

warming

Decreased snow and ice; less reflectivity

More solar radiation absorbed at surface

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Initial Change

Climate warming

Increased clouds

Greater reflected radiation

Reduced Warming

Cloud Radiative Feedbacks

Uncertain

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FEEDBACKS INVOLVED IN GLOBAL WARMING

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CLIMATE SENSITIVITY

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CLIMATE SENSITIVITY

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The ‘commitment’ to future warming

CLIMATE SENSITIVITY