🏝️Earth Science Unit 5 – Earth's Atmosphere and Climate

Atmospheric Structure and Composition

• Consists of several distinct layers: troposphere, stratosphere, mesosphere, thermosphere, and exosphere
  • Troposphere extends from Earth's surface to ~12 km (7.5 mi) and contains 75% of atmospheric mass
  • Stratosphere sits above troposphere, extends to ~50 km (31 mi), and contains ozone layer that absorbs UV radiation
• Primarily composed of nitrogen (78%) and oxygen (21%), with trace amounts of argon, carbon dioxide, and water vapor
• Atmospheric pressure decreases exponentially with altitude due to gravity's effect on air molecules
• Contains suspended particulates like dust, pollen, and pollutants that affect air quality and climate
• Ozone layer in stratosphere protects Earth's surface from harmful UV radiation
  • Depletion of ozone layer due to human activities (CFCs) led to Montreal Protocol in 1987
• Atmospheric composition has changed over Earth's history due to volcanic eruptions, biological processes, and human activities

Energy Balance and Heat Transfer

• Earth's energy balance involves incoming solar radiation and outgoing terrestrial radiation
  • Incoming shortwave radiation from the Sun is absorbed, reflected, or scattered by the atmosphere and Earth's surface
  • Outgoing longwave radiation is emitted by Earth's surface and atmosphere, some of which is trapped by greenhouse gases
• Greenhouse effect warms Earth's surface by trapping heat in the atmosphere
  • Caused by gases like carbon dioxide, water vapor, and methane that absorb and re-emit longwave radiation
• Heat transfer occurs through radiation, conduction, and convection in the atmosphere
  • Radiation is the transfer of energy through electromagnetic waves (sunlight)
  • Conduction is the transfer of heat through direct contact between molecules (air in contact with Earth's surface)
  • Convection is the transfer of heat through the movement of fluids (rising warm air and sinking cool air)
• Earth's energy budget is the balance between incoming and outgoing energy
  • Imbalances can lead to climate change over time
• Albedo is the reflectivity of a surface, which affects how much solar radiation is absorbed or reflected
  • Snow and ice have high albedo, while oceans and forests have low albedo

Weather Patterns and Phenomena

• Weather is the day-to-day state of the atmosphere, including temperature, humidity, precipitation, and wind
• Influenced by factors like air pressure, temperature gradients, and moisture content
• High and low pressure systems drive wind patterns and weather conditions
  • High pressure systems are associated with clear skies and calm weather
  • Low pressure systems are associated with stormy weather and precipitation
• Jet streams are fast-moving air currents in the upper atmosphere that steer weather systems
• Fronts are boundaries between air masses of different temperatures and densities
  • Cold fronts occur when cold air displaces warm air, often bringing thunderstorms and strong winds
  • Warm fronts occur when warm air displaces cold air, often bringing steady rain and cloudy conditions
• Thunderstorms develop due to instability in the atmosphere and can produce lightning, heavy rain, and hail
• Tornadoes are violently rotating columns of air that extend from a thunderstorm to the ground
• Hurricanes are large, rotating storms that form over warm ocean waters and can bring strong winds, heavy rain, and storm surges

Climate Systems and Factors

• Climate is the long-term average of weather patterns in a particular area
• Influenced by factors like latitude, altitude, ocean currents, and atmospheric circulation patterns
• Köppen climate classification system categorizes climates based on temperature and precipitation patterns
  • Includes five main climate types: tropical, dry, temperate, continental, and polar
• Milankovitch cycles are long-term variations in Earth's orbit and axis tilt that affect global climate patterns
  • Eccentricity, obliquity, and precession cycles operate on timescales of tens to hundreds of thousands of years
• El Niño and La Niña are opposite phases of a naturally occurring climate pattern in the Pacific Ocean
  • El Niño brings warmer ocean temperatures and increased rainfall to the eastern Pacific
  • La Niña brings cooler ocean temperatures and decreased rainfall to the eastern Pacific
• Feedback loops can amplify or dampen climate change effects
  • Positive feedback loops (ice-albedo, water vapor) enhance initial changes
  • Negative feedback loops (carbon cycle, cloud formation) counteract initial changes

Atmospheric Circulation and Wind Patterns

• Atmospheric circulation is driven by uneven heating of Earth's surface and the Coriolis effect
• Hadley cells are large-scale circulation patterns that transport heat from the equator to the mid-latitudes
  • Rising motion at the equator, descending motion at ~30° latitude (subtropical high pressure belts)
• Ferrel cells are mid-latitude circulation patterns that transport heat from the subtropics to the polar regions
  • Rising motion at ~60° latitude, descending motion at ~30° latitude
• Polar cells are small-scale circulation patterns that transport cold air from the poles to the mid-latitudes
• Trade winds are persistent easterly winds that blow from the subtropical high pressure belts towards the equator
• Westerlies are prevailing winds that blow from west to east in the mid-latitudes
• Jet streams are fast-moving air currents in the upper atmosphere that flow from west to east
  • Polar jet stream is located at ~60° latitude and influences weather patterns in the mid-latitudes
  • Subtropical jet stream is located at ~30° latitude and influences weather patterns in the subtropics
• Monsoons are seasonal wind patterns that bring heavy rainfall to certain regions (South Asia, West Africa)
  • Caused by differential heating of land and ocean surfaces

Climate Change and Global Warming

• Climate change refers to long-term changes in global or regional climate patterns
• Caused by factors like variations in solar output, volcanic eruptions, and human activities
• Global warming is the long-term warming of Earth's surface and lower atmosphere
  • Primarily caused by increasing atmospheric concentrations of greenhouse gases due to human activities (fossil fuel combustion, deforestation)
• Greenhouse gases like carbon dioxide, methane, and water vapor trap heat in the atmosphere
  • Atmospheric CO2 levels have increased from ~280 ppm (pre-industrial) to ~415 ppm (2021)
• Impacts of climate change include rising sea levels, more frequent and intense heatwaves and droughts, and changes in precipitation patterns
  • Sea level rise is caused by thermal expansion of ocean water and melting of land-based ice sheets (Greenland, Antarctica)
  • Heatwaves and droughts are becoming more common and severe in many regions
  • Changes in precipitation patterns can lead to more frequent flooding or water scarcity
• Mitigation strategies aim to reduce greenhouse gas emissions and limit the magnitude of future climate change
  • Includes transitioning to renewable energy sources, improving energy efficiency, and implementing carbon pricing mechanisms
• Adaptation strategies aim to reduce the impacts of climate change on human and natural systems
  • Includes building sea walls, developing drought-resistant crops, and improving early warning systems for extreme weather events

Atmospheric Monitoring and Forecasting

• Atmospheric monitoring involves measuring and tracking various atmospheric variables
  • Includes temperature, pressure, humidity, wind speed and direction, and air quality
• Weather stations on land and buoys in the ocean provide surface-based measurements
• Weather balloons (radiosondes) provide vertical profiles of atmospheric variables
• Satellites provide global coverage of atmospheric and surface conditions
  • Geostationary satellites orbit at ~36,000 km and provide continuous coverage of a specific region
  • Polar-orbiting satellites orbit at ~800 km and provide global coverage twice daily
• Radar and lidar systems provide information on precipitation, cloud cover, and wind patterns
• Numerical weather prediction models use atmospheric data and physical equations to simulate future weather conditions
  • Models are run on supercomputers and provide forecasts for various time scales (short-range, medium-range, long-range)
• Ensemble forecasting involves running multiple model simulations with slightly different initial conditions
  • Provides a range of possible outcomes and helps quantify forecast uncertainty
• Forecast verification involves comparing model predictions with actual observations to assess forecast accuracy and improve future models

Human Impact on Atmosphere and Climate

• Human activities have significantly altered the composition of the atmosphere and the Earth's climate system
• Burning of fossil fuels (coal, oil, natural gas) releases carbon dioxide and other greenhouse gases into the atmosphere
  • Deforestation also contributes to increased atmospheric CO2 by reducing carbon uptake by plants
• Emissions of air pollutants like sulfur dioxide, nitrogen oxides, and particulate matter can degrade air quality and harm human health
  • Can also affect climate through the formation of aerosols, which can absorb or scatter solar radiation
• Chlorofluorocarbons (CFCs) released by human activities have depleted the stratospheric ozone layer
  • Montreal Protocol (1987) successfully phased out the production of CFCs and other ozone-depleting substances
• Land use changes like urbanization and agriculture can alter local and regional climate patterns
  • Urban heat island effect occurs when cities are warmer than surrounding rural areas due to reduced vegetation, increased heat absorption by buildings and pavement, and anthropogenic heat sources
• Geoengineering proposals aim to deliberately modify the Earth's climate system to counteract the effects of global warming
  • Includes solar radiation management (stratospheric aerosol injection) and carbon dioxide removal (direct air capture, ocean iron fertilization)
  • Geoengineering is controversial due to potential unintended consequences and ethical concerns
• Mitigating human impact on the atmosphere and climate requires a coordinated global effort to reduce greenhouse gas emissions, transition to clean energy sources, and adopt sustainable land use practices