Lecture 3: Radiation and Earth’s Atmosphere EarthsClimate_Web_Chapter.pdf, p. 1-5 • The earth’s global average surface temperature in present climate is 15C (59F).
Download ReportTranscript Lecture 3: Radiation and Earth’s Atmosphere EarthsClimate_Web_Chapter.pdf, p. 1-5 • The earth’s global average surface temperature in present climate is 15C (59F).
Lecture 3: Radiation and Earth’s Atmosphere EarthsClimate_Web_Chapter.pdf, p. 1-5 • The earth’s global average surface temperature in present climate is 15C (59F). Without the atmosphere, it would be -18C (-0.4F), • About 33C or 59.4F colder! Atmosphere is the most important component of the earth’s climate. • Radiation vs. other heat sources: • Total energy enter the earth’s atmosphere: 174 petawatts or 174X1015 Watts • Solar: 99.978%, Geothermal: 0.013%, waste and fossil fuel: 0.007%, tidal: 0.002% For more advanced reading materials, please see http://www.geo.utexas.edu/courses/387h/ScheduleGPC_detail.htm Earth’s Atmosphere 1. What is it? A thin gaseous envelope around the planet. Blue sky! 2. Composition Today’s atmosphere: nitrogen (78%), oxygen (21%), other (1%) – trace gases! Nitrogen, oxygen, argon, water vapor, carbon dioxide, methane, and most other gases are invisible. Clouds are not gas, but condensed vapor in the form of liquid droplets or ice particles. Ground based smog, which is visible, contains reactants of nitrogen and ozone. Four layers: 3. Structure Troposphere (overturning) From surface to 8-18 km Stratosphere (stratified) Mesosphere Thermosphere From troposphere top to 50 km The Structure of Earth’s Atmosphere 1. Four layers defined by temperature Troposphere: T decreases with elevation Stratosphere: T increases with elevation Mesosphere: T decreases with elevation Thermosphere: T increases with elevation 2. Importance to climate and climate change Troposphere: 80% of Earth’s gases Most of Earth’s weather happens Most of the measurements Stratosphere: 19.9% of Earth’s gases Ozone layer: Blocking Sun’s ultraviolet radiation Energy from the Sun 1. Characteristics Travels through space (vacuum) in a speed of light In the form of waves: Electromagnetic waves In stream of particles (Photons) Releases heat when absorbed 2. Electromagnetic spectrum From short wavelength, high energy, gamma rays to long wavelength, low energy, radio waves 3. Importance to climate and climate change Primary driving force of Earth’s climate engine Ultraviolet, Visible, Infrared Sun’s Electromagnetic Spectrum Solar radiation has peak intensities in the shorter wavelengths, dominant in the region we know as visible, thus shortwave radiation Blackbody Radiation Curves Any object above absolute zero radiates heat, as proportional to T4 Higher temperature, shorter wavelength Longwave & Shortwave Radiation The hot sun radiates at shorter wavelengths that carry more energy, and the fraction absorbed by the cooler earth is then re-radiated at longer wavelengths. Atmospheric Greenhouse Effects T= 15°C (59°F) With the Surface Temperature Atmosphere T= –18°C (0°F) Surface Temperature Without the Atmosphere Greenhouse effects make Earth’s surface warmer! Greenhouse Gases What are they? Water vapor (H2O) Carbon dioxide (CO2) Ozone (O3) Methane (CH4) Chlorofluorocarbons (CFC’s) Nitrous oxide (N2O) Water vapor accounts for 60% of the atmospheric greenhouse effect, CO2 26%, and the remaining greenhouse gases 14%. CO2 contributes most (55-60%) to the anthropogenic greenhouse effect, and methane is a distant second (16%). CFCs cause the strongest greenhouse warming on a molecule-for-molecule basis. Nitrous Oxide Atmospheric Absorption Solar radiation passes rather freely through Earth's atmosphere. Earth emits longwave energy, which either leaks through a narrow window or is absorbed by greenhouse gases and radiated back to Earth. Absorption (100%) Methane Ozone Water Vapor Carbon Dioxide UV IR Total Atmo Wavelength Solar Intensity and Latitude Solar intensity, defined as the energy per area, is different at different latitude. A sunlight beam that strikes at an angle is spread across a greater surface area, and is a less intense heat source than a beam impinging directly. Unequal Radiation on a Sphere Insolation is stronger in the tropics (low latitudes) than in in the polar regions (high latitudes). Pole-to-Equator Heating Imbalances What controls the elevation of the Sun above the horizon? Earth’s Tilt Primarily Determines Season Earth's Annual Energy Balance The balance is achieved locally at only two lines of latitude. A global balance is maintained by excess heat from the equatorial region transferring toward the poles. Incoming Solar Radiation Outgoing Longwave Radiation Unequal heating of tropics and poles The Global Energy Budget: Driver of Atmospheric Motion A balance exists between the incoming solar and outgoing longwave energy averaged over the globe and the year SURPLUS DEFICIT However, the tilt of the Earth means this balance is not maintained for each latitude Questions: • What is the current global mean surface temperature? • Why it is 33C or 59F warmer than it would be without the atmosphere? • Why is climate dominated by the radiation balance of the atmosphere? • What are the main greenhouse gases in the earth’s atmosphere? • In what latitudes the earth’s gain and lost radiative energy (heat), respectively? Questions: • What is the current global mean surface temperature? – 15C or 59F • Why it is 33C or 59F warmer than it would be without the atmosphere? – Because of greenhouse effect of the atmosphere • Why is climate dominated by the radiation balance of the atmosphere? – It contributes to 99.978% of total heat flux into the atmosphere • What are the main greenhouse gases in the earth’s atmosphere? – H2O, CO2, CH4, O3, CFCs, NO2 • In what latitudes the earth’s gain and lost radiative energy (heat), respectively? – Gain heat in the tropics or 40S-40N, loss heat in high latitudes (50S-50N) Interested in more questions? Try these questions: • Can you name one or more main causes of glacier and interglacier climate change? • What is the most important greenhouse gases for modern climate change? What is the fastest growing greenhouse gas? • Earth’s climate has been much colder and warmer than that of today. Do you know in what ways the earth’s radiation balance was altered?