The Earth’s Atmosphere

The Atmosphere

The atmosphere is made up of an envelope of gases whose composition has remained relatively stable through most of Earth’s history. Degree of difference in heating and rotation of our planet contribute to the dynamic nature of our atmosphere, and the consequent changes in force, pressure, and temperature create climate zones, weather patterns, and storms on our planet.

Misconceptions About the Earth’s Atmosphere

• A common misconception is that land plants generate most of the oxygen in the atmosphere.

• Most people falsely believe that direct sunlight heats the atmosphere.

• Another common misconception is that greenhouse gases make up a major portion of the atmosphere.

Radiative Balance

• Earth's surface temperature has been remarkably constant over geologic time.

• Earth exchanges energy with its environment primarily through transfers of electromagnetic radiation.

• The most abundant gases in the atmosphere—nitrogen, oxygen, and argon—neither absorb nor emit terrestrial or solar radiation. – But clouds, water vapor, and some relatively rare

greenhouse gases (GHGs) such as carbon dioxide, methane, and nitrous oxide in the atmosphere can absorb long-wave radiation

Major GHGs

• Carbon dioxide (CO2), the most significant GHG directly affected by anthropogenic activity, is the product of the oxidation of carbon in organic matter.

• Methane (CH4) is produced by anaerobic decay of organic material.

• Nitrous oxide (N2O) is produced by fertilizer use, animal waste management, fossil fuel combustion, and industrial activities.

Major GHGs

• Hydrofluorocarbons (HFCs) and perfluorocarbons (PFCs) are synthetic chemicals that are used in a variety of industrial production processes such as semiconductor manufacturing. PFCs are also produced as a by-product of aluminum smelting.

The Carbon Cycle

Carbon Cycle Activity

Atmosphere •1 black

Land Biomass •4 black

Ocean •1 red; 2 black

Fossil Fuel •7 black

Rock •1 white

The Carbon Cycle

Do you agree with the number of balloons in each location? Use this diagram to guide your reasoning…

The Carbon Cycle

1. Describe two important “sinks” (parts of Earth that store carbon), two important “sources” (parts of Earth that release carbon), and one important “release agent” (conditions that trigger release) for carbon.2. Currently it seems that CO2 sources are out of balance with CO2 sinks. If more CO2 is produced than sinks can remove, CO2 in the atmosphere increases. What might happen if the reverse were true and sinks took up more CO2 than sources released?3. Why is knowledge about the carbon cycle important for helping scientists understand global climate change?

Vertical Motion in the Atmosphere

• What causes motion in the atmosphere?• When a column of air is heated, it becomes

less dense which increases its buoyancy and convection occurs.

• Water vapor reported as relative humidity is the total amount of water vapor that can be held in the air at a given temperature.– Consequently, atmospheric water vapor

concentrations are highest in warm regions and decrease toward the poles

Contribution of H2O

• Atmospheric water vapor contributes to weather patterns in several ways

• First, adding water vapor to the air reduces its density

• Secondly, moist air carries latent energy.• The dew point, another key weather variable,

denotes the temperature to which air would have to cool to reach 100 percent relative humidity.

How Clouds Form

When conditional instability exists, air parcels are stable if they are dry and unstable if they are saturated. Conditional instability can help to generate storms by causing parcels of moist air to rise and form towering clouds.

Movement of Air Mass

• Convection is not the only process that lifts air from lower to higher altitudes.

• Convergence occurs when air masses run together, pushing air upward.

• When warm and cold air fronts collide, the denser cold air slides underneath the warm air layer and lifts it. In each case, if warm air is lifted high enough to reach its dew point, clouds will form.

Atmospheric Circulation Patterns

Sea breezes are caused by temperature differences between land at the surface and adjoining water, which cause air to flow in opposite directions during the day and at night.

Atmospheric Circulation Patterns

• Winds that move over very long distances appear to curve because of the Coriolis force, an apparent force caused by Earth's rotation.

• This phenomenon occurs because all points on the planet's surface rotate once around Earth's axis every 24 hours, but different points move at different speeds

Atmospheric Circulation Patterns

Atmospheric Circulation Patterns

Climate, Weather and Storms

Climate vs. Weather

• Climate refers to long-term weather trends and the range of variations that can be detected over decades.

• Specific weather trends describe annual meteorological happenings in a given area.

• The global air circulation patterns create predictable regional climate zones.

Global Air Circulation

• Because the Coriolis effect prevents mass and heat from moving readily to polar latitudes, temperatures decline and pressures increase sharply between middle latitudes and the polar regions, creating currents in the atmosphere known as the “jet stream”.

Hurricanes

• Hurricanes form over tropical waters (between 8° and 20° latitude) in areas with high humidity, light winds, and warm sea surface temperatures, typically above 26.5°C (80°F).

• At the ocean's surface a feedback loop sometimes develops: falling pressure pulls in more air at the surface, which makes more warm air rise and release latent heat, which further reduces surface pressure.

Hurricane

Hurricane wind speeds range from 74 miles per hour (the minimum for a Category 1 storm on the Saffir/Simpson scale) to more than 155 miles per hour for Category 5 storms.

Mid-latitude Cyclones

Mid-latitude cyclones occur when warm and cold air masses collide around a center of low pressure.

Mid-latitude Cyclones

• Mid-latitude cyclones cause most of the stormy weather in the United States, especially during the winter season.

• They occur when warm tropical and cold polar air masses meet at the polar front (coincident with the jet stream).

The Global Carbon Cycle

• One of the key issues in current atmospheric science research is understanding how GHG emissions affect natural cycling of carbon between the atmosphere, oceans, and land.

• Today, human intervention in the carbon cycle is disturbing this natural balance.

• Two processes remove CO2 from the atmosphere: photosynthesis by land plants and marine organisms, and dissolution in the oceans.

Carbon Reservoir

• The residence time of carbon varies widely among different reservoirs.– A carbon atom spends about 5 years in the

atmosphere. – It spends 10 years in terrestrial vegetation.– It spends 380 years in intermediate and deep

ocean waters. – Carbon can remain locked up in ocean sediments

or fossil fuel deposits for millions of years.

Feedbacks in the Atmosphere

• Feedbacks are interactions between climate variables such as temperature, precipitation, and vegetation and elements that control the greenhouse effect.

• Positive feedbacks amplify temperature change by making the greenhouse effect stronger.

• Negative feedbacks have a dampening effect on temperature change, making the climate system less sensitive to the factors that trigger them.

Feedbacks in the Atmosphere

• Water vapor feedback (positive). • Cloud feedback on terrestrial radiation

(positive). • Cloud feedback on solar radiation (negative). • Vegetation feedback on solar radiation

(negative). • Ice-albedo feedback on solar radiation

(positive).

Feedbacks in the Atmosphere

• Feedbacks cause much of the uncertainty in today's climate change models, and more research is needed to understand how these relationships work.