Global Climate Change Notes

Global Climate Change - Chapter 15

Introduction

• The Earth is experiencing an unprecedented rate of carbon dioxide (CO2) increase in the atmosphere, unseen since major climate catastrophes of the past.
• Quoting Neil deGrasse Tyson: "We are dumping CO2 into the atmosphere at a rate the Earth hasn't seen since the great climate catastrophes of the past… The dinosaurs never saw the asteroid coming. What's our excuse?"

Key Concepts

• Role of greenhouse gases in climate change.
• Sources of greenhouse gases.
• Earth’s energy budget and global temperature changes.
• Influence of positive and negative feedback mechanisms on climate.
• Understanding past climates in the geologic past.
• Environmental changes due to anthropogenic climate change.
• Causes of recent climate change and the role of humans.

Weather vs. Climate

• Weather: Short-term, constantly changing atmospheric conditions.
• Climate: Long-term, generalized composite of weather conditions.

Elements of Weather and Climate

• Measured regularly to understand weather and climate.
• Key Elements:
  • Temperature
  • Humidity
  • Cloudiness
  • Precipitation
  • Air pressure
  • Wind speed and direction

Composition of the Atmosphere

• Air is a mixture of discrete gases.
• Major components of clean, dry air:
  • Nitrogen (N2): $78 \%$
  • Oxygen (O2): $21 \%$
  • Argon (Ar): $0.934 \%$
  • Carbon Dioxide (CO2): $0.0405 \%$ (405 ppm), absorbs heat energy from Earth

Variable Components of Air

• Water Vapor
  • Up to about $4 \%$ of the air's volume.
  • Forms clouds and precipitation.
  • Absorbs heat energy from Earth.
• Aerosols
  • Tiny solid and liquid particles.
  • Water vapor condenses on these.
  • Reflect sunlight and help color sunrise and sunset.
• Ozone (O3)
  • Three atoms of oxygen.
  • Concentrated between 10 and 50 km above the surface.
  • Absorbs harmful UV radiation.
  • Depleted by human activity (CFCs).
  • Pollutant at the surface, damaging vegetation and harmful if inhaled.

Antarctic Ozone Hole

• October 1, 2016: Ozone hole reached 23 million km² (8.9 million mi²), nearly as large as North America.

Vertical Structure of the Atmosphere

• Pressure Changes
  • Pressure is the weight of the air above.
  • One-half of the atmosphere is below 3.5 miles (5.6 km).
  • Ninety percent of the atmosphere is below 10 miles (16 km).
• Temperature Changes
  • Air temperature drops with increasing height in the troposphere.

Atmospheric Layers

• Troposphere
  • Bottom layer.
  • Temperature decreases with altitude (environmental lapse rate).
    • $6.5°C$ per kilometer (average), or $3.5°F$ per 1000 feet (average).
  • Thickness varies, average height is 12 km.
  • Outer boundary: tropopause.
• Stratosphere
  • About 12–50 km.
  • Temperature increases at the top.
  • Outer boundary: stratopause.
• Mesosphere
  • About 50–80 km.
  • Temperature decreases.
  • Outer boundary: mesopause.
• Thermosphere
  • No well-defined upper limit.
  • Fraction of atmosphere’s mass.
  • Gases moving at high speeds.

Earth-Sun Relationships

• Earth Motions
  • Rotates on its axis.
  • Revolves around the Sun.
• Seasons
  • Result of changing Sun angle and changing length of daylight. Earth's axis is inclined $23.5°$.

Solstices and Equinoxes (Northern Hemisphere)

• Summer Solstice
  • June 21–22.
  • Sun’s vertical rays at the Tropic of Cancer ($23.5°$ N latitude).
• Winter Solstice
  • December 21–22.
  • Sun’s vertical rays at the Tropic of Capricorn ($23.5°$ S latitude).
• Autumnal Equinox
  • September 22–23.
  • Sun’s vertical rays at the Equator ($0°$ latitude).
• Spring (Vernal) Equinox
  • March 21–22.
  • Sun’s vertical rays at the Equator ($0°$ latitude).

Energy, Heat, and Temperature

• Heat is transferred from warmer to cooler objects.
• Mechanisms of heat transfer:
  • Conduction: Through molecular activity.
  • Convection: Mass movement within a substance (usually vertical motions).
  • Radiation: Electromagnetic radiation.
    • Velocity: 300,000 kilometers (186,000 miles) per second in a vacuum.

Radiation

• Consists of different wavelengths (Gamma, Radio waves, Visible, etc.).
• Laws governing radiation:
  • All objects emit radiant energy.
  • Hotter objects radiate more total energy.
  • Hotter objects radiate more energy as shorter wavelengths.
  • Good absorbers are also good emitters.

Heating the Atmosphere

• Atmosphere mostly transparent to incoming solar radiation.
• Atmospheric effects:
  • Reflection (albedo = percent reflected)
  • Scattering
  • Absorption
• About 50 percent of incoming radiation is absorbed at Earth’s surface.

Earth's Energy Budget

• Earth reradiates radiation (infrared = heat) as terrestrial radiation at longer wavelengths.
• Longer wavelength terrestrial radiation is absorbed by carbon dioxide and water vapor, creating the greenhouse effect.

Greenhouse Effect

• Bodies with modest amounts of greenhouse gases like Earth: Atmosphere absorbs some long-wave radiation and reradiates some energy back to the surface, keeping Earth's surface $33°C$ ($59°F$) warmer than it would otherwise be.
• Bodies with abundant greenhouse gases like Venus: Venus experiences extraordinary greenhouse warming, which is estimated to raise its surface temperature by $523°C$ ($941°F$)..

Air Temperature Data

• Daily maximum and minimum.
• Other measurements:
  • Daily mean temperature.
  • Daily range.
  • Monthly mean.
  • Annual mean.
  • Annual temperature range.
• Isotherms:
  • Lines connecting points of equal temperatures on a map.
  • Used to show distribution of air temperatures.
• Temperature gradient: amount of temperature change per unit of distance.

Why Temperatures Vary: Controls of Temperature

• Land and Water
  • Land heats more rapidly and to higher temperatures than water.
  • Water has high specific heat: amount of energy needed to raise the temperature of 1 gram of a substance $1°C$.
• Altitude
  • Higher altitudes have lower temperatures.
• Geographic Position
  • Windward vs. Leeward coasts.
• Cloud Cover and Albedo
  • Clouds have high albedo.
  • Cool air during the day, keep heat in at night.

World Distribution of Temperature

• Temperature maps use isotherms to show temperature distribution.
• Temperatures adjusted to sea level.
• January and July are used for analysis because they represent temperature extremes.
• Global temperature patterns:
  • Temperature decreases poleward from the tropics.
  • Isotherms exhibit a latitudinal shift with the seasons.
  • Warmest and coldest temperatures occur over land.
  • In the Southern Hemisphere, isotherms are straighter and more stable.
  • Isotherms show ocean currents.
  • Annual temperature range:
    • Small near the equator.
    • Increases with an increase in latitude.
    • Greatest over continental locations.

Climate Change

• Climate Change: A change in climate patterns attributed largely to the use of fossil fuels.
• Global Warming: A gradual increase in the overall temperature of the earth's atmosphere attributed to the greenhouse effect.

Greenhouse Effect

• Increased gas levels in lower atmosphere that trap in heat energy.
• Greenhouse Gases:
  • Carbon Dioxide - $81 \%$
  • Methane - $10 \%$
  • Nitrous Oxide - $6 \%$
  • Fluorinated Gasses - $3 \%$

Contributing Factors to Climate Change

1. Fossil fuel burning power plants.
2. Burning of gasoline for transportation.
3. Deforestation of the rainforests.
4. Methane emissions from animals and agriculture.

Potential Effects of Climate Change

1. Worldwide sea level rise from melting ice.
2. More frequent and intense storms.
3. Massive crop failures.
4. Widespread extinctions.
5. Loss of coral reefs.

Sea Level Rise

• $90 \%$ of the US population lives within 100 miles of the ocean, and if sea levels were to rise, these areas would be inundated.