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Earth's Atmosphere

• Today we will talk about the part of Earth that is most important to our survival - the atmosphere

• Earth's atmosphere is unique in the Solar System and has changed greatly over time

• Recent changes may be leading to global warming and an increased threat to life on Earth

Atmospheric Layers

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• As altitude increases, pressure decreases and the air becomes 'thinner'

• Surprisingly, temperature does not constantly decrease, but fluctuates throughout the different layers

Atmospheric Layers• The troposphere is the lowest

layer, rising to ~12 km above the surface with decreasing temperature

• Temperature increases through the stratosphere up to ~45 km above the surface (airplanes fly in the lower stratosphere)

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• The last layer is the ionosphere, where sunlight breaks up molecules/atoms and increases the temperature slightly

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The Troposphere• The troposphere is the layer in

which we live

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• All weather on the Earth is caused by convection

• Hot air near the surface rises, cools at higher altitudes, then falls back

• This circulation produces wind, thunderstorms, weather fronts, hurricanes, etc.

The Ozone Layer

• Ozone is simply 3 oxygen atoms joined together (O3)

• This molecule is found in abundance at the bottom of the mesosphere

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• This protective layer prevents most UV light from reaching the surface

Destruction of the Ozone

• Manmade chlorofluorocarbons (CFC's) are present in some aerosol sprays and refrigeration equipment (freon)

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• Chlorine atoms are highly reactive with ozone, and they steal away an oxygen atom

• Eventually, the chlorine-oxygen molecule reacts with another oxygen, leaving the chlorine atom to break up more ozone

While O3 blocks UV light, O2 does not, creating a hole in the protective layer.

One chlorine atom can break up 100,000 ozone molecules!

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Banning CFC's

• In the late 80's and 90's, many nations agreed to begin phasing out CFC's from many of their products

• Progress has been made, but it will take decades to eliminate all CFC's from the atmosphere

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Why is the Sky Blue?• The sun emits all colors from red to

blue, so why does the sky appear blue?

• When sunlight hits our atmosphere, the gas and dust scatter some of the light

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• This means the bluer light gets spread over the entire sky, while the redder light comes directly from the Sun

• Note that when the Sun is low in the sky, the light is passing through much more atmosphere and even the red light becomes scattered

This type of scattering is known asRayleigh scattering.

Evolution of Our Atmosphere

• The primary (first) atmosphere of the Earth would have consisted mainly of the elements found in the solar nebula, like hydrogen and helium

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• The secondary atmosphere of the Earth was formed when volcanic activity released carbon dioxide, sulfur dioxide, and nitrogen compounds into the atmosphere

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Evolution of Our Atmosphere• Many of the nitrogen

compounds were broken up by UV light, leaving lots of atmospheric nitrogen

• Other compounds, like CO2

and SO2, became trapped in the Earth's surface or in the oceans

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Natural Greenhouse Effect• Outside the effects of man, there

have always been natural amounts of greenhouse gases like CO2 and water vapor in the atmosphere

• Remember, greenhouse gases block infrared radiation from escaping into space, increasing the temperature at the planet's surface

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Earth without greenhouse effect:

-23oC or -9oF

Earth with greenhouse effect:

22oC or 72oF

Runaway Greenhouse Effect

• We have already seen on Venus how the greenhouse effect can scorch a planet if taken too far

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• The hotter the planet, the more CO2 is released from rocks, tundra, and the ocean

• Ice reflects more light than water -as more ice melts, the Earth absorbs more and more heat

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Is It Real?

• We know how the greenhouse effect works and what causes it

• We know that runaway greenhouse effect can lead to increased global temperatures

• What evidence is there that global warming is occurring?

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YES NO

Do you believe global warming is real?

YES NO

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Global Temperature• We know that the Earth naturally undergoes warm and cool

periods (ice ages)

• From a variety of sources (tree rings, sediment layers, isotope ratios in coral, etc.) we can trace temperature back centuries

Recent Global Temperature

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Is Global Warming Real?

• There are long term warming and cooling trends in the past 2,000 years, as well as many sharp increases and decreases

• However, the increase in temperature in the last 30 years is more drastic than any seen in the current record

• Keep in mind that this is average global temperature (it doesn't necessarily mean it will be hotter everyday of the year where you live)

Are We Responsible?

• So we have established that there is a recent significant increase in global temperatures

• We only have a record of ~2,000 years, so this could just be a large natural warming trend

• Is there any evidence that humans may be the cause for the increased temperatures?

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YES NO

Are humans the main cause?

Yes No

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CO2 in the Atmosphere

• Carbon dioxide is the most common greenhouse gas

• The majority of the world's energy comes from the burning of fossil fuels (coal, gas, oil) which releases large amounts of carbon dioxide

• Is the human contribution enough to offset the global balance?

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CO2 in the Atmosphere

What happened in world history

around this time?

Maybe a Natural Trend? - NO!

Need More Proof?

Human Population

CO2 Emissions

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Are We the Main Cause?

• There is no doubt that since the industrial revolution, there has been a major increase in the amount of carbon dioxide in the atmosphere

• There is also no doubt that increased amounts of CO2 in the atmosphere will produce an enhanced greenhouse effect and increase temperatures on the surface

• Put the two together ...

Will It Affect Us in Our Lifetimes?

• This is the most controversial question we have faced, as evidenced by the quiz

• Many would say small effects can be seen already

• But will major changes occur in our lives?– The answer shouldn't

matter ...

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YES NO

YES NO

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Affect climate/world in our lifetime?

Glacial Melting• Evidence for increased

temperatures are seen around the world with receding glaciers

• In the past 60 years (a lifetime) many glaciers have shrunken by miles in size

• Glacier National Park has gone from ~150 glaciers in 1850 to ~35 today– There will be none left by

~2030

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Arctic and Antarctic Ice• The ice depth of the arctic is dropping rapidly (50% of the

ice gone by 2050's)

• Many cargo lines are planning to be able to cross ice-free paths through the arctic in the summer in the next 10 years

-0.9m

-1.3m

-0.9m

-1.4m-1.7m

-1.8m

Arctic and Antarctic Ice• Ice at the south pole is melting at a drastic rate as well

• Changes in the amount and location of ice has a drastic effect on a variety of species in these food chains

Larsen B ice shelf, 17th Feb 2002 Larsen B ice shelf, 5th March 2002 (16 days later)

Where Does All the Ice Go?

• The melting ice will eventually lead to large changes in the global sea level

• The major sea currents (such as the Gulf Stream) will become disrupted as the ice disappears and water rises

• The less ice on the surface, the less reflective the surface, and the heating intensifies

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Global Sea Levels

Buoy depth over the past 200 years.

Changes in the Weather

• Remember that all weather is tied to convection, which is itself tied to the heating of the Earth's surface

• As more heat becomes available, more energetic storms will be produced (hurricanes, thunderstorms, drought, wildfires, etc)

• There is much debate on whether these changes are already occurring

Changes in Economy

• Global warming is a lose-lose situation as far as the world-wide economy is concerned

• Increased disasters and strain on natural resources will cost governments an increasing amount of money over time

• Any attempts to curb CO2 emissions will also cost industrial nations greatly

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Changes in Health• Climate change leads to a

change in the natural habitat range for many disease carrying insects (like mosquitoes)

• Increased medical costs and preparations strain nations already financially burdened

• Undeveloped countries have even less access to fresh, clean water

Changes in Government

• A decrease in the amount of fertile land will cause dramatic changes in global politics

• Some models show drought conditions will occur for the majority of the Midwest, while former tundra in Canada and Siberia will open up large tracts of farming land

• When the food supply of a nation like America is threatened, how far would we go?

Past the Point of No Return?

• There are many scientists who believe that conditions will worsen severely over the next 100 years whether action is taken or not

• The current political climate is not favorable for a worldwide commitment to curb global warming

• It will be our generation who shoulders the majority of the burden