ENV200 Chapter 9 Notes

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Department
School of Environment
Course
ENV200H1
Professor
Romila Verma
Semester
Winter

Description
CHAPTER 9 – CLIMATE [9.1] WHAT IS THE ATMOSPHERE? ­ Weather = daily temperatures, wind, and precipitation that occurs in the troposphere ­ Climate = long-term temperatures and precipitation trends ­ The earliest atmosphere consisted mainly of hydrogen and helium, but has since diffused into space o Volcanic emissions added carbon, nitrogen, oxygen, and sulfur to the atmosphere o Photosynthetic blue-green bacteria, algae, and green plants added molecular oxygen (2 ) ­ Air = 78% nitrogen + 21% oxygen + 1% argon, carbon dioxide, and other gases o Water vapour = H 2 in gas form o Aerosols = minute particles and liquid droplets that are suspended in the air o Water vapour and aerosols in the atmosphere play important roles in the earth's energy budget and in rain production ­ Four atmospheric layers that vary in temperature (and composition) due to differences in absorption of solar energy o Troposphere  Air circulates in vertical and horizontal convection currents  Convection currents = circulate air, moisture, and heat around the globe  Contains 75% of the total mass of the atmosphere  Much denser because gravity holds most air molecules close to the earth’s surface  Ranges in depth from 18 km over the equator to 8 km to over the poles  Temperature decreases with increasing altitude o Tropopause = temperature boundary between troposphere and stratosphere created due to sudden reversal of temperature gradient  Little mixing  Tropospheric air cannot continue to rise when it is cooler than the surrounding air o Stratosphere (ozone layer)  Temperature increases with increasing altitude  Warmer than the upper troposphere  More dilute than the troposphere  Similar composition to troposphere, except:  Contains almost no water vapour  Contains a large amount of ozone gas  Depletion of stratospheric ozone by chemical pollutants increases UV radiation reaching the earth’s surface  Ozone (O 3 molecules absorb solar energy (e.g., UV radiation)  UV radiation damages living tissues, increases skin cancer, and damages biological communities  Relatively calm  Little mixing  Volcanic ash and human-caused contaminants can remain in suspension for years o Mesosphere (middle layer)  Temperature decreases with increasing altitude o Thermosphere (heated layer)  Temperature increases with increasing altitude  Contains highly ionized (electrically charged) gases, which are heated by high-energy solar and cosmic radiation  Lower thermosphere  Intense pulses of high-energy radiation cause ions to glow o Ions = electrically charged particles  Phenomenon is known as the aurora borealis (northern lights) and aurora australis (southern lights) o No sharp boundary marks the end of the atmosphere  Pressure and density decrease with distance from the earth until they become indistinguishable from the near-vacuum of interstellar space The atmosphere captures energy selectively ­ Insolation = incoming solar radiation o 25% is reflected as infrared energy by clouds and atmospheric gases  Albedo = reflectivity  Fresh snow and dense clouds have high albedo (or reflect energy)  Black soil, asphalt, and water have low albedo (or absorb energy) o 25% is absorbed by carbon dioxide, water vapor, ozone, and methane  Warms the atmosphere slightly  Heats materials (e.g., asphalt)  Evaporates water  Provides energy for photosynthesis in plants  Follows the second law of thermodynamics  Absorbed light energy is gradually re-emitted as heat energy o Light = high-intensity energy o Heat = low-intensity energy  Change in energy intensity is important o Gases in the atmosphere allow light energy to pass through o Gases in the atmosphere absorb or reflect heat energy o Water vapor (H 2), carbon dioxide (CO2), methane (CH 4, and nitrous oxide (N2O) are most effective at trapping re-radiated heat energy  Energy capture is necessary for water and for life o Increases earth’s average surface temperature o Greenhouse effect = the capture of energy by gases in the atmosphere  Atmosphere also lets the energy dissipate gradually to space  Balance of the rate of incoming energy and outgoing energy determines the temperature inside the greenhouse o Adding greenhouse gases (e.g., CO2, CH4, N2O) to the atmosphere is slowing the rate of heat loss, thus increasing heat storage in our “greenhouse” o 50% reaches the earth’s surface  Most energy is in the form of light or infrared (heat) energy Evaporated water stores and redistributes heat ­ Most of the incoming solar energy is used to evaporate water o Latent heat = heat stored in water vapour  Water evaporation converts solar energy into latent heat  Contains huge amounts of energy ­ Redistribution of latent heat and water around the globe is essential to life ­ Rain falls when there are two conditions: o A moisture source (e.g., ocean)  Water is evaporated into the atmosphere o A lifting mechanism  Air cools at high elevations  Moisture in the cooling air condenses, which falls as rain or snow Ocean currents also redistribute heat ­ Warm and cold ocean currents strongly influence climate conditions on land ­ Surface ocean currents = results from wind pushing on the ocean surface ­ Deeper ocean currents = deep water wells up to replace the moving surface water ­ Gyres = huge cycling ocean currents o Redistribute heat from low latitudes to high latitudes ­ Thermohaline (temperature and salinity-related) circulation = surface water and deep water circulation system o Temperature and salt concentrations control the density of water o Differences in water density drive ocean movements [9.2] CLIMATE CHANGES OVER TIME Ice cores tell us about climate history ­ Small amounts of air are trapped in the snow ­ New layers of snow compress lower layers into ice, but the tiny air bubbles still remain ­ Each bubble is a tiny sample of the atmosphere at the time that snow fell ­ Collect air bubble samples in ice cores/sheets to show how the atmosphere has changed over time o Proportions of oxygen isotopes  Water molecules with lighter oxygen atoms evaporate more easily  Used to determine atmospheric temperatures o Concentrations of atmospheric CO 2  Strong correlation between CO c2ncentrations and atmospheric temperatures What causes natural climatic swings? ­ Ice core records show that there have been repeated, cyclical climate changes over time ­ Modest changes correspond to cycles in the sun's intensity ­ Dramatic changes correspond to periodic shifts in the earth's orbit, tilt, and wobble o Milankovitch cycles  Orbital eccentricity = the earth's elliptical orbit stretches and shortens  Tilt variation = the earth's axis changes its angle of tilt  Axial wobble = the earth’s axis wobbles like an out-of-balance spinning top  When the wobble orients the north pole toward the sun, the northern summers are warm and there is overall warming of the earth  When the wobble orients the north pole away the sun, the northern summers are cold and there is overall cooling of the earth  Cause variation in the intensity of incoming solar energy at different latitudes  Cause variation in the intensity of summer heating or winter cooling  Explain the cold/warm cycles in the ice cores ­ Volcanic eruptions can cause sudden climate shifts, but usually only for a few years o Sulfuric acid and particulate material are ejected into the atmosphere  Dim incoming sunlight  Cool the whole planet o Volcanoes are a notable but not dominant factor in recent climate trends El Niño/Southern Oscillation is one of many regional cycles ­ Climate changes according to oscillations in the ocean and atmosphere on the scale of years or decades ­ El Niño/Southern Oscillation (ENSO) = most well-known coupled ocean-atmosphere oscillation o Affects weather across the Pacific and adjacent continents o Causes heavy monsoons or serious droughts ­ During most years… o Warm pool of surface water in the Pacific Ocean sloshes slowly back and forth between I
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