The Atmosphere, Part 1: Composition, Structure, & Heat Budget Thomas V. Dagenhart, M.S. v 3.8 Crepuscular Rays, Manassas, VA; Dagenhart, 2003

Atmospheric Composition Reported on a dry basis, water vapor excluded since it’s so variable. Only 2 gases comprise 99% Water vapor normally <1 - 4% Minor gases exert influence far greater than their abundance would suggest, e.g. greenhouse effect, UV protection, photosynthesis, etc. Gross & Gross, 1996

Dynamic Equilibrium of Atmospheric Water Vapor Atmospheric water vapor varies immensely with place and time. For Earth as a whole, evaporation equals precipitation. For ocean as a whole, evaporation exceeds precipitation. Latent heat of vaporization supplies much of heat to drive convection. Gross & Gross, 1996

Air parcels change size & temperature as they rise & fall. Rising & cooling triggers condensation which forms clouds & rain. Latent heat released at condensation further warms air and forces more rising. Garrison, 2005

Layers of the Atmosphere The exosphere tails off into space and meets the solar wind. The ionosphere straddles several layers. The ionosphere reflects radio waves & hosts the aurora borealis & aurora australis. Ionosphere Wikipedia, 2009

Structure & Temperature Profile of Lower Atmosphere Virtually all weather occurs in troposphere. Earth’s surface heats troposphere from bottom; favors vertical mixing. Stratosphere heated most at middle & top because of UV ray absorption by ozone; limits vertical convective mixing there. Additional layers found above: mesosphere, thermosphere, exosphere. strongest heating by UV-absorbing ozone heating from below Gross & Gross, 1996

Sun Angle Controls Sunlight Intensity At low angles, sunlight spreads over much larger areas & thus heats less effectively. At low angles, sunlight reflects from water & ice more efficiently. Garrison, 2005

Variation of Solar Radiation with Latitude (also with Seasons and with Time of Day) 2 cal/cm 2 /min. at top of atmosphere perpendicular to sun’s rays 0.5 cal/cm 2 /min. on the average at top of atmosphere due to inclination of sun’s rays Even less reaches surface on the average Intensity = 2 x sine (sun’s <) (cal/cm 2 /min.) noon radiation intensity (cal/cm 2 /min.) at given latitude on equinox o = o = o = 0.02 At winter solstice (N.H.) the most intense radiation is at Tropic of noon. Gross & Gross, 1996

Earth-Sun Relations To Polaris (North Star)

Emission Spectrum of Sun & Earth Wavelength (micrometers) UV solar radiation near IR solar radiation visible solar radia- tion Sun’s “surface” at 6000 o C radiates strongly in UV, visible, & near IR. Earth’s surface & atmosphere at 18 o C radiate strongly in far IR. Consider area under curve when comparing relative intensities of UV, visible & IR. Gross & Gross, 1996

Global Heat Budget These numbers indicate global averages. Locally the energy fluxes vary with season, time of day, cloud cover, snow cover, vegetation patterns, etc. Garrison, 2005 Absorbed Visible Light Converted to IR, Sensible & Latent Heat X 16% X 5% X 39% Greenhouse Effect + =

Latitudinal Variations in Radiation Budget Surplus must equal deficits to maintain heat budget. Garrison, 2005 Excess heat lost near poles must be carried from tropics to poles by ocean currents & winds.

Poleward Heat Transport to Balance Unequal Heating Equator would be hotter & poles would be much colder without this transport. Transport by winds & ocean currents. Garrison, 2005

The Greenhouse Effect Certain atmospheric gases absorb outbound infrared (IR) radiation and then reradiate it in all directions including downward. Some of the reradiated IR reaches the ground and lower atmosphere to make the Earth warmer than it would be without the greenhouse gases. Much like the glass of a greenhouse allows in light but traps heat. Without any greenhouse gases, Earth would chill to –18 o C. Water is the main greenouse gas, but it’s self limiting due to precipitation. Garrison, 2005 CH 4

Greenhouse Effect Is it the main cause of global warming? Or is the climate cycling due to ice age causes? Tarbuck & Lutgens, 2005 CO 2 CH 4 CFC

Greenhouse Gases Other gases help CO 2. All have significant natural sources except CFC’s. Methane = natural gas from swamps & rice paddies, oil & gas wells, coal mines, land fills, cow & termite flatulence, & decomposition. CFC’s being phased out, used in AC and as propellants (hair spray). Low altitude ozone partly from man’s pollution. N 2 O from burning, lightning, moist soils. CH 4 CO 2 N2ON2O O3O3 e.g. CCl 2 F 2 Percentage indicates relative importance, not relative abundance. Gross & Gross, 1996 Cow s Greenhouse Gas on BBC

Relative Global Temperature Variation Mean annual temperatures are indicated as a deviation from the global mean. 5 o C total temperature rise since last ice age (18,000 years BP) or 0.03 o C per century, about half of rise is due to increasing solar output. The 0.5 o C rise in the last 25 years looks very significant, = 2 o C per century. Garrison,

Global Warming Since begins the period where thermometer readings are available worldwide. Annual averages for entire world compared to averages for Larger rise projected during 21st century. Tarbuck & Lutgens, 2008

CO 2 Concentration Vs. Time Has risen rapidly since industrial revolution due to fossil fuel burning. Many natural sources: volcanoes, burning, respiration, decomposition. Rise is less than expected. Key cause of greenhouse effect. Fossil Fuels = coal, oil, natural gas, peat Garrison, 2005

CO 2 may be approaching 3X the preindustrial level in 2100.

What causes the zig zag detail in the curve? Graph by Dagenhart from data in EPA, 2002.

Rising Carbon Dioxide (CO 2 ) Levels Rapid rise from coal, gas, and oil burning since Causes greenhouse effect, i.e. global warming. Missing CO 2 puzzle: concentration is lower than predicted by emissions. Storage in ocean or plants? Tarbuck & Lutgens, 2005

Sea Level Change in Last 20,000 Years Water supplied by rapid glacial retreat. Little change in last 6,000 years. 100 m rise in 11,000 years = 9.1 mm/yr average 18.2 m/yr horizontal shoreline shift on VA Coastal Plain Tarbuck & Lutgens, 2005

Projected Sea Level Rise in This Century Three different estimates. Note the accelerating rate of rise! Worldwide changes are termed eustatic sea level changes. Tarbuck & Lutgens, 2005

Causes of Sea Level Sea Level Rise This Century Note the Antarctic Ice Sheet may actually grow in spite of global warming & limit sea level rise. 57% of the sea level rise will result from simple expansion of seawater as it warms. Tarbuck & Lutgens, 2005

Effects of Rising Sea Level I-95 Coastal Plain Virginia Beach X Uplift along an active continental margin may offset sea level rise in CA Like the East coast in early Tertiary time. Like the West coast. Tarbuck & Lutgens, 2005

Coastline Variation Due To Glacially- Induced Sea Level Changes Not “Waterworld” ~ 100 m drop ~ 80 m rise Tarbuck & Lutgens, 2005

What does rising sea level mean to islanders? Land is inundated & barrier reef provides less wave protection. Great tsunami of December 2004 washed over this island. Many died. Island in Maldives Garrison, 2005

Do Jet Contrails, Dust, & Smoke Increase Reflection of Sunlight and Reduce Global Warming? Contrail = condensation trail Sublimation trail really? After 911 terrorist attack planes were grounded & contrails were absent, a small percentage increase in solar radiation was detected. Satellite Photograph of Contrails & Ship Smoke Trails over Pacific Ocean; Garrison, 2005

The Ultimate Proof of Global Warming Let me be brief.

Stratospheric Ozone Layer Depletion Stratospheric ozone shields us from UV rays; prevents skin cancer. Ozone depletion due to chlorofluo- rocarbons (CFC’s) from man’s pollution. Depletion partly due to natural processes? Observation only carried out for a limited time. Ozone at ground level comes from pollution & irritates lungs. Ozone “Hole” in Stratosphere Over Antarctica Garrison, 2005

Variation of CFC-11 Levels from A leveling off & slight dip in CFC levels appears to be happening as a result of CFC phase out after 1990 treaty. Garrison, 2005

Risks from Increased UV Radiation Higher incidence of skin cancers and mutations. Loss of phytoplankton & zooplankton from upper 2 m of ocean. Damage to land plants & reduced crop yields. Eye cataracts. Immune system suppression Malignant Melanoma, Garrison, 2005 A 1% decrease in ozone is expected to produce a 5- 7% increase in skin cancer.

Decreased Phytoplankton Productivity As southern hemisphere summer begins. Due to increased influx of UV rays through ozone hole over Antarctica. Phytoplankton around Antarctica form the base of a food chain critical to whales and remove much CO2 from atmosphere. Garrison, 2005

Monthly Variation in Ozone Concentrations NASA, 2005 Ozone Video Note ozone hole over Antarctica (dark blue). Note ozone depleted belt near equator (light blue) moves N & S with seasons.

References Environmental Protection Agency (2002) Global Warming Web Site. Garrison, T. (2005) Oceanography: An Invitation to Marine Science, 5th ed. Brooks/Cole Thomson Learning, Stamford, CT, 522 p. Gross, M.G. and E. Gross (1996) Oceanography: A View of the Earth, 7th ed. Prentice Hall, Upper Saddle River, NJ, 472 pp. Tarbuck, E.J. and F.K. Lutgens (2005) Earth: An Introduction to Physical Geology, 8th ed. Pearson-Prentice Hall, Upper Saddle River, NJ, 711 p. Sunrise at OHS, Manassas, VA; Dagenhart, 2003