The Atmosphere and the Water Cycle

Earth’s system’s have two sources of energy

• Internal • External

These Systems Create Heat for our Planet

Driven by Sunlight and the Earth’s internal heat a number of cycles

continously circulate energy through the Earth’s system.

The Sun is the major source of Earth’s energy

• More than 99% of the Earth’s Energy comes from the Sun

The Sun’s Energy Drives our Weather and Climate

• The energy from the Sun is circulated into our atmosphere and drives our weather

It’s a two way street

• The Energy from the Sun is transferred to the Earth mostly through visible light

• The Earth sends energy back into outer space mostly through infrared radiation.

A Two Way Energy Street

The transfer of incoming energy and outgoing energy is nearly equal

• To maintain equilibrium, the Earth returns the energy it receives from the Sun back to space as infrared light. However, only 6% of the energy goes directly from the Earth’s surface to space.

The Greenhouse Effect

• About 15% of the Earth’s surface energy is absorbed by water vapor, carbon dioxide and other gases in the atmosphere. This is called the greenhouse effect and is a common condition on planets with relatively thick atmospheres.

The Earth’s Atmosphere is always changing

• Currently the Earth’s Atmosphere is made up of mainly three gases.

• Nitrogen (78%)

• Oxygen (21%)

• Argon (0.9%)

These gases have changed over time, and are changing now.

• The atmosphere is constantly in flux.

• Natural processes absorb and release gases all the time.

• However, there is some concern about greenhouse gases increasing due to our use of fossil fuels.

The History of our Atmosphere

• Volcanic outgassing is believed to have contributed water vapor, carbon dioxide, carbon monoxide, sulfur dioxide, hydrogen sulfide, chlorine and nitrogen. As gases in the primordial atmosphere reacted, ammonia and methane formed.

The Arrival of Oxygen

• Primitive photosynthetic organisms began filling the warm oceans. Oxygen was produced as CO2 was consumed.

• Ancient cyanobacteria produced a great deal of O2.

• These bacteria changed the atmosphere and the face of the planet.

Earth’s Atmosphere Slows Down

• As Earth matured and cooled, its rate of geothermal outgassing decreased.

• While Earth’s atmosphere does still change, it does so at a slower pace than early in our history.

• Natural events are still of consequence, and more recently, human activities have made significant changes to the composition of the atmosphere.

The Greenhouse Effect

• The greenhouse effect is not a bad thing.• The retention of energy from the sun keeps the

planet warm.

When the Greenhouse effect goes bad

• Most people are concerned about the concentration of greenhouse gasses in the atmosphere.

• In too great a concentrations, the gasses might absorb much of the infrared radiation that is radiated from Earth’s surface, and lead to a dangerous increase in global temperatures.

Greenhouse Gases

• The greenhouse gases which are of greatest importance are: water vapor, carbon dioxide, methane, nitrous oxide, chlorofluorocarbons and halocarbons.

Is CO2 going up too quickly?

• In the last 250 years the levels of Carbon Dioxide in the atmosphere have increased greatly.

• Levels of CO2 have been increasing since the industrial revolution.

Is CO2 the key to global warming?

• There have been times in the past when there was much more CO2 in the atmosphere.

• Like most gases in the atmosphere, CO2 has changed over time.

• Scientists are currently examining the changing atmosphere in great detail to try and determine exactly how the atmosphere is changing and why.

Is the Earth Warming too quickly?

• The question is what concentration of greenhouse gases will cause excessive absorption of infrared radiation.

• It is a question, currently, without a definitive answer.

The Sun and the Weather

• Global Warming aside, the sun is the main force behind the Earth’s Weather.

• As the Sun’s rays strike the Earth some are reflected and some are absorbed.

Albedo

• The Albedo of an object determines how much light it reflects.

• A high albedo reflects a lot of energy from the sun.

• A low albedo reflects a smaller amount.

Radiation vs. Convection

• Radiation is how the energy from the sun reaches us. It is the transfer of energy without the involvement of a physical substance in the transmission.

• Convection transmits heat energy by transporting groups of molecules from one place to another within a substance.

Convection• As energy is circulated through the Earth’s

atmosphere it is involved in the process of Convection

Convection

• Convection occurs as a result of warmer, less dense portions of the medium rising while the cooler, more dense portions sink.

• The warmer the fluid (liquid or gas) in contrast to the temperature of the surrounding medium, the quicker and more forceful the convection which ensues.

Convection currents cause winds

Why is weather complicated?

• If Convection is a simple process, then why is it so hard to predict the weather?

Earth’s Rotation Affects Wind and Ocean Currents

• The Earth is rotating once every 24 hours.

• Earth’s Rotational speed varies from the Equator to the poles.

• Earth rotates faster at the equator.

• This difference in rotational speed causes the Coriolis effect.

The Coriolis Effect

• As the Earth rotates it causes a deflection in winds either clockwise or counterclockwise.

• Thus air currents behave differently in the Northern or Southern Hemisphere.

The Coriolis Effect

Weather, Currents, and Convection

• The uneven surface of the Earth, combined with the Coriolis effect cause a number of different wind patterns, or cells around the globe.

These Convection Cells Create Winds

• Strong winds around the globe create weather patterns.

• These winds can also create ocean currents.

Ocean Currents and Weather

• These wind and ocean currents affect weather around the globe.

• These ocean currents make some places warm, and others cold.

• They can also cause huge seasonal storms.