Chapter 1 Introduction to the Climate System

1. Chapter 1 Introduction to the Climate System • This chapter discusses: • Earth’s atmosphere • Oceans • Cryosphere (sea ice/glacial ice) • Land and biosphere

2. The Effects of the Atmosphere • Blocks ultraviolet radiation • Meteors burn • Sound waves can travel • Birds and airplanes can fly • Diffuses heat • Scatters sunlight (blue skies and sunsets) • Hydrologic cycle • Weather and climate

3. The Atmosphere • A thin envelope around the planet • 90% of its mass (5.1 x 1018 kg) is within 16 km (10 mi) of the surface (about 0.0025 times the radius of the Earth) • Atmospheric motions can therefore be considered to occur “at” the Earth’s surface • The basic chemical composition of dry air is very uniform across the globe and up to about 100 km • The greatest and most important variations in its composition involve water in its various phases • Water vapor • Clouds of liquid water • Clouds of ice crystals • Rain, snow and hail

4. TRACE GASES Argon (.93%) and Carbon Dioxide (.03%) Ozone (.000004%) Composition of the Atmosphere Dry Air Solid particles (dust, sea salt, pollution) also exist Water vapor is constantly being added and subtracted from the atmosphere, and varies from near 0% (deserts) to 3-4% (warm, tropical oceans and jungles)

5. Greenhouse Gases • Nitrogen, Oxygen and Argon (99.9% volume mixing • ratio) have only limited interaction with incoming • solar radiation, and they do not interact with the • infrared radiation emitted by the Earth • A number of trace gases (carbon dioxide, methane, • nitrous oxide, and ozone) do absorb and emit • infrared radiation (as does water vapor) • Water vapor, carbon dioxide and ozone also absorb • solar shortwave radiation • Because they emit infrared radiation up- and • downward, these greenhouse gases increase the • energy received at the Earth’s surface, thus raising • the temperature

7. Changing Atmospheric Composition: Indicators of the Human Influence Global, well-mixed greenhouse gas (GHG) concentrations CO2 • 31% increase since 1750: Highest levels • since at least 420,000 years ago • Rate of increase unprecedented over • at least the last 20,000 years 1000 1200 1400 1600 1800 2000 Year 1000 1200 1400 1600 1800 2000 Year CH4 • Increased 150% since 1750 to its highest • levels in at least 420,000 years • Has both natural (e.g., wetland) and • human-influenced sources (e.g., landfills, • agriculture, natural gas activities) • Accounts for 20% of total GHG forcing N2O • Increased 16% since 1750 to its highest • levels in at least 1,000 years • Has both natural (e.g., soils and oceans) • and anthropogenic sources • Accounts for 6% of total GHG forcing • Halocarbons (e.g., CFCs) account for 14%

8. Changing Atmospheric Composition: Indicators of the Human Influence Global, well-mixed greenhouse gas (GHG) concentrations CO2 • 31% increase since 1750: Highest levels • since at least 420,000 years ago • Rate of increase unprecedented over • at least the last 20,000 years CH4 • Increased 150% since 1750 to its highest • levels in at least 420,000 years 1000 1200 1400 1600 1800 2000 Year 1000 1200 1400 1600 1800 2000 Year N2O • Increased 16% since 1750 to its highest • levels in at least 1,000 years • Has both natural (e.g., soils and oceans) • and anthropogenic sources • Accounts for 6% of total GHG forcing • Halocarbons (e.g., CFCs) account for 14%

9. Changing Atmospheric Composition: Indicators of the Human Influence Global, well-mixed greenhouse gas (GHG) concentrations CO2 • 31% increase since 1750: Highest levels • since at least 420,000 years ago • Rate of increase unprecedented over • at least the last 20,000 years CH4 • Increased 150% since 1750 to its highest • levels in at least 420,000 years N2O • Increased 16% since 1750 to its highest • levels in at least 1,000 years 1000 1200 1400 1600 1800 2000 Year

10. Atmospheric CO2 Since 1750

11. Composition of the Present Atmosphere Venus Earth Mars Surface Pressure 100,000 mb 1,000 mb 6 mb CO2 >98% 0.03% 96% N2 1% 78% 2.5% Ar 1% 1% 1.5% O2 0.0% 21% 2.5% H2O 0.0% 0.1% 0–0.1%

12. The Vertical Structure of Earth’s Atmosphere Four layers: Troposphere (overturning) From surface to 8-18 km Stratosphere (stratified) From troposphere top to 50 km Absorption of solar radiation by O3 Mesosphere Extremely thin air; very low temperature Thermosphere Extremely thin air; very high temperature

13. Vertical Structure of the Atmosphere 4 distinct layers determined by the change of temperature with height

14. Extends to 10 km in the extratropics, 16 km in the tropics • Contains >80% of the atmospheric mass, and 50% is • contained in the lowest 5 km (3.5 miles) • It is defined as a layer of temperature decrease • The total temperature change with altitude is about 72°C • (130°F), or 6.5°C per km (lapse rate) • It is the region where most weather occurs, and it is kept • well stirred by rising and descending air currents • Near 11 km resides the “jet stream” • The transition region of no temperature change is the • “tropopause”: it marks the beginning of the next layer

15. Vertical Structure of the Atmosphere 4 distinct layers determined by the change of temperature with height

16. Extends to about 50 km • It is defined as a layer of temperature increase and • is stable with very little vertical air motion – a good place to fly! • Why does temperature increase? In part because of ozone, formed • as intense ultraviolet solar radiation breaks apart oxygen molecules • Near the ozone maximum (about 25 km), there are still only • 12 ozone molecules for every million air molecules • Yet, the absorption of ultraviolet radiation by ozone shields the • surface and warms the stratosphere • The transition region to the next layer is the “stratopause”

17. Vertical Structure of the Atmosphere 4 distinct layers determined by the change of temperature with height

18. Extends to about 85 km • Few ozone molecules, and the extremely thin air loses more energy • than it gains, so the temperature decreases with height • With so few molecules to scatter light, the sky is dark • The air pressure is 1000 times lower than at the surface • (99.9% of the atmosphere’s mass is below the mesosphere) • Exposure to solar radiation would severely burn our bodies! • The transition region to the next layer is the “mesopause”

19. Vertical Structure of the Atmosphere 4 distinct layers determined by the change of temperature with height

20. Contains 0.01% of the atmospheric mass • An air molecule can travel 1 km before colliding with another! • If we measure temperature with a thermometer, the reading • is near absolute zero (0 K, or -460°F), not 1500°F. Why? • The temperature of a gas is related to the average speed at • which molecules are moving • Even though air molecules in this region are zipping around at very • high speeds, there are too few to bounce off a thermometer bulb • to transfer energy to record a reading • This explains why astronauts on space walks can survive such high • temperatures: the traditional meaning of “hot” and “cold” is no • longer applicable

21. Vertical Structure of Earth’s Atmosphere 1. Four layers defined by temperature Troposphere: T decreases with altitude T increases with altitude Stratosphere: Mesosphere: T decreases with altitude Thermosphere: T increases with altitude 2. Importance to climate and climate change • Troposphere: Contains 80% of Earth’s gases Most of Earth’s weather occurs Most of the measurements is available • Stratosphere: Contains 19.9% of Earth’s gases Ozone layer: Blocking Sun’s ultraviolet radiation

22. Atmospheric Temperature 1. Most widely recognized climatic variable (Global warming) Tc = TK – T0 Tc = temperature in degrees Celsius (°C) = 5(TF – 32)/9 TK = thermodynamic temperature in kelvins (K) T0 = 273.15 K = the freezing point Global mean surface temperature = 288 K, 15°C, 59°F 2. The lapse rate • Γ≡ – ∂T/∂z, Γ > 0 in the troposphere * Varies with altitude, season and latitude * Global mean = 6.5 K km-1 * Determined by a balance between radiative cooling and convection of heat * Γ< 0, temperature inversion At high latitudes in winter and spring

23. Atmospheric Temperature (continued) 3. Pole-to-pole distribution of zonal-mean temperature * Greatest near the equator, > 26°C; lowest at the poles * Stronger seasonal cycle in the Northern Hemisphere than in the south * Amplitude of the seasonal cycle decreases from the poles to the equator 4. Geographic distributions • * Land heats up and cools down much more quickly than oceans, hence larger seasonal variations. * Large seasonal variations in North America and Asia * Smaller seasonal variations in the Southern Hemisphere. SeeIRI Data Library

24. Annual Climate in Seattle

27. Atmospheric Pressure Pressure=Force/Area Pressure decreases with altitude. Gravity pulls gases toward earth's surface, and the whole column of gases weighs 14.7 psi at sea level, a pressure of 1013.25 mb or 29.92 in.Hg. Standard sea level pressure = 101325 Pa = 101.325 kPa = 1013.25 mb

28. Vertical Pressure Profile Pressure decreases at a curved rate proportional to altitude squared, but near the surface a linear estimate of 10 mb per 100 meters works well.

29. -dp p+dp dz p gρdz z Hydrostatic Balance Force = Mass × Acceleration Given a unit area with thickness dz, volume = dz, mass = ρdz Gravity force= g ρdz Pressure force= –dp Without atmospheric motions, –dp = gρdz dp/dz = – ρg p(z) = ∫z∞ ρg dz m(z)=p(z)/g m(0)=p(0)/g=ps/g =1.03×104 kg m–2

30. -dp p+dp dz p gρdz z Hydrostatic Balance (continued) dp/dz = – ρg For an ideal gas, p=ρRT where the gas constant R = 287 J K-1 kg-1 dp/dz=–pg/(RT) dp/p= –dz/H d lnp= –dz/H where H=RT/g=scale height If the atmosphere is isothermal, ∫psp d lnp= ∫0z–dz/H p=psexp(–z/H) H = 7.6 km for the mean T

31. Water Vapor 1. Highly variable spatially • Less than 1% in a dry atmosphere • More than 3% in the moist tropics • Decreases rapidly with altitude; most is within a few km of the surface • Decreases rapidly with latitude; at the equator is 10 times that at the poles 2. Importance to climate and climate change • * Important part of the water cycle; ocean-to-land atmospheric vapor transport balances land-to-ocean runoff. • * The most important greenhouse gas: water vapor-temperature feedback. • * Water vapor condenses to form clouds, thus clouds–radiation feedback. Clouds release rainfall, reflect solar radiation, and reduce the infrared radiation emitted by Earth.

32. Oceans Area: covers ~70% of Earth’s surface Volume: ~97% of all the water on Earth Depth: ~3.5 kilometers Albedo: 5-10%, lowest on Earth’s surface Heat capacity: high; thermal inertia: high Temperature: less variable than in the atmosphere Freezing point: –1.9°C, not 0°C Salinity: water and dissolved salts; most common salt: table salt (NaCl). Density: 1034-1035 kg/m3 (greater than pure water 1000kg/m3) Average salinity = 35 parts per thousand (ppt) or 3.5% by weight Density depends on temperature and salinity: Cold water  high density Formation of sea ice  high density Evaporation  high salinity  high density Precipitation and river discharge  low salinity  low density Two main forms of circulation Surface currents: wind-driven, horizontal, surface waters, fast Deep-ocean circulation: thermohaline, vertical, deep waters, slow Surface is not level due to currents, waves, atmosphere pressure, and variation in gravity.

33. Sea Ice Locations: in the Arctic Ocean surrounded by landmass; in the Southern Ocean, surrounding Antarctica. Depth: ~1–4 m in the Arctic; ~1 m in the Southern Ocean. Longevity: in the Arctic, 4–5 yrs; in the Southern Ocean, forms and melts yearly. Albedo: 60-90%, highest on Earth’s surface Density: less than seawater, hence floats on top. The role in the climate system: Albedo-temperature feedback Prevents the underlying (warm) ocean from interaction with the atmosphere, thus cools the air. Melting of sea ice extracts heat from the atmosphere; Formation of sea ice releases heat to the atmosphere.

34. Glacial Ice Two forms: Mountain (alpine) glaciers Continental ice sheets. Locations: Near sea-level at hi. lat. > 5 km near equator Antarctica and Greenland (polar ice caps) Sizes: A few km in length, tens to hundreds of m in width and thickness. Hundred to thousands of km in length, 1–4 km in thickness. Area of the two current ice sheets: ~11% of land surface; 70 m sea level rise when all melted. Movement: Flows downhill by gravity along mountain valleys Flows to the lower margins. The weight depresses bedrock. Albedo: 60-90%, highest on Earth’s surface The role in the climate system: Stores 70% of world’s fresh water Changes salinity, circulation and sea level when melt Albedo-temperature feedback

35. Example of a positive feedback More energy retained in system Albedo decreasesLess solar energy reflected Warm temperatures Ice and snow melt If this were the only mechanism acting, we’d get a runaway temperature increase

39. The law of the minimum:the factor that is least available has the greatest effect on plants. The law of the maximum:too much of a certain factor also limits a plant’s existence. Global Climate Pattern and Vegetation Af: tropical wet (rainforest); Aw: tropical wet and dry (savanna); Am: tropical monsoon Bs: dry semiarid (steppe); Bw: dry arid (desert) Cs: mediterranean; Cfa: humid subtropical; Cfb: marine Dw: dry winters; Ds: dry summers; Df: wet all seasons ET: polar tundra; EF: polar ice caps

40. Satellite-Derived Plant Geography Satellite remote sensing provides global, systematic, continuous measurements. Monitor land use and land cover changes. Quantitative. Must be validated by comparing with ground-based data. Early maps are constructed based on atlas, surface surveys. Emphasize climate factors (Precip, Temp). Neglect human factors.