Earth & Space Science Chapter 11: Heating the Atmosphere

Weather and Climate

• Weather refers to the state of the atmosphere at a given place and time
• Climate is the aggregate or average weather of a location, including variations and extremes

Composition of the Atmosphere

• The atmosphere is a mixture of many gases, each with its own physical properties
• Dry, clean air is composed of:
  • Nitrogen (78%)
  • Oxygen (21%)
  • Argon (0.93%)
  • Carbon dioxide (0.0391%)
  • Other gases (0.01%)
• Carbon dioxide is an efficient absorber of energy and plays a significant role in heating the atmosphere

Importance of Carbon Dioxide

• CO2 concentrations have been rising over the past 200 years
• Increased CO2 concentrations have contributed to the warming of the Earth's atmosphere, which may affect climate

Water Vapor and Aerosols

• Water vapor is a significant component of the atmosphere, varying from 0% to 4% by volume
• Water vapor is the source of all clouds and precipitation
• Aerosols are tiny solid and liquid particles suspended in the air, playing a significant role in weather and climate
• Examples of aerosols: sea salt, soil, smoke, pollen, and volcanic ash

Ozone

• Ozone is a form of oxygen that combines three oxygen atoms into each molecule (O3)
• Ozone is concentrated in the stratosphere, where it absorbs large quantities of UV radiation from the Sun
• Ozone is crucial to life on Earth, and reducing its amount can adversely impact life

Vertical Structure of the Atmosphere

• Atmospheric pressure decreases with altitude
• Temperature is used to divide the atmosphere into four layers:
  • Troposphere
  • Stratosphere
  • Mesosphere
  • Thermosphere
• Each layer has distinct characteristics, such as temperature and pressure changes

Earth-Sun Relationships

• The Earth's axis is tilted at 23 ½°, generating seasonal changes
• The length of daylight and Sun angle affect the amount of energy received by the Earth's surface
• The Earth's distance from the Sun varies throughout the year, with perihelion (91.5 million miles) and aphelion (94.5 million miles)

Energy, Heat, and Temperature

• Heat and temperature are not synonymous
• Heat is energy possessed by a material, while temperature refers to the intensity or degree of "hotness"
• Heat is transferred by three mechanisms:
  • Conduction
  • Convection
  • Radiation

Radiation

• Radiation is the transfer of energy through electromagnetic waves
• The sun is the ultimate source of energy for the Earth's weather
• Electromagnetic radiation includes:
  • Radio waves
  • Visible light
  • Infrared radiation
  • Ultraviolet radiation
  • Gamma rays

Heating the Atmosphere

• Solar radiation is absorbed, transmitted, and reflected by the Earth's surface and atmosphere
• The atmosphere is heated by energy that is first absorbed by the Earth's surface and then reradiated to the atmosphere (terrestrial radiation)
• The greenhouse effect is a natural phenomenon, where gases in the atmosphere absorb and reradiate energy, trapping heat and warming the planet.### Human Impact on Global Climate
• The combustion of fossil fuels has added large amounts of CO2 to the atmosphere, contributing to the greenhouse effect.
• Deforestation and subsequent burning and decay of organic material generate CO2, and remove plant material that would otherwise utilize CO2 during photosynthesis.
• It is estimated that 45% of excess CO2 remains in the atmosphere, and current CO2 levels are 30% higher than they have been in the past 650,000 years.
• According to the Intergovernmental Panel on Climate Change (IPCC), most of the observed increase in average global temperatures since the 1950s are the result of human-generated greenhouse gas.
• Global temperatures have increased by approximately 0.6°C (1.0°F) since the 1970s, and 0.8°C (1.4°F) during the 20th century.
• The greatest amount of warming has occurred in Arctic and high-latitude regions.
• Instrument records indicate that the warmest 16 years occurred from 1995 to 2011, and global mean temperatures are higher than at any time in the last 500 to 1,000 years.
• The average temperature of the global ocean has increased to a depth of 3,000 meters (10,000 feet).

Climate Change Consequences

• If CO2 concentrations double from pre-industrial levels to 560 ppm, the likely temperature increase will be between 2°C and 4.5°C (3.5°F to 8.1°F).
• Sea level may rise, the paths of large-scale storms may change, and changes in the distribution of wet and dry regions may develop.
• Tropical systems may become more intense, and droughts and heat waves may increase in number and frequency.

Air Temperature Data

• Temperature is recorded at weather stations on a continuous basis, including high and low temperatures, daily mean temperature, daily range, monthly mean, and annual mean.
• Isotherm maps are used to visualize temperature distribution over a large area, with lines representing 5° or 10° temperature differences.
• The temperature gradient is the amount of temperature change per unit of distance.

Controls of Temperature

• Differences in the amount of solar radiation received are the most important cause of temperature variations.
• Variations in sun angle and length of daylight depend on latitude, resulting in warmer temperatures near the tropics and colder temperatures near the poles.
• Seasonal changes occur due to the migration of the sun's vertical rays.
• Other factors contributing to temperature variations include:
  • Differential heating of land and water
  • Altitude
  • Geographic position
  • Cloud cover and albedo
  • Ocean currents

Differential Heating of Land and Water

• Land heats more rapidly and to higher temperatures than water, and cools more rapidly and to lower temperatures than water.
• Reasons for differential heating include:
  • Water has a higher specific heat than land
  • Land surfaces are opaque, while water is transparent
  • Surface water mixes with water below, distributing heat through a larger mass
  • Evaporation from water is greater than from land surfaces

Altitude and Geographic Position

• Altitude can play a significant role in determining a location's temperature, with temperatures dropping 6.5°C per km in the troposphere.
• Coastal locations with prevailing winds from the ocean experience different temperatures than those with prevailing winds from the land.
• Windward coasts experience the moderating effects of the ocean.

Cloud Cover and Albedo

• Cloud cover can cause temperatures to be lower during the day due to increased reflection, and higher at night due to absorption of terrestrial radiation.
• Snow- and ice-covered landscapes have high albedos, which is why glaciers don't completely melt in the summer and why snow may still be present on mild spring days.

World Distribution of Temperature

• World isotherm maps show temperature variations, with the greatest temperature extremes occurring in January and July.
• Trends observed from these maps include:
  • Temperature decreases poleward from the tropics
  • Isotherms exhibit a latitudinal shift with the seasons
  • Warmest and coldest temperatures occur over land
  • Isotherms show ocean currents
  • In the Southern Hemisphere (water hemisphere), isotherms are straighter and more stable, while in the Northern Hemisphere (land hemisphere), isotherms bend and are more varied due to seasonal changes.
  • Annual temperature ranges are small near the equator, increase with an increase in latitude, and are the greatest over the continents.

Explore the impact of weather on human lives and the economy. Learn how human activities influence the atmosphere and its behavior.