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Sea Ice Reflects suns waves (energy) Permanent on the poles (volume changes, but never completely melts ~ 4m thick Sea water freezes at ~2 º C not 0 º C Leaves behind salts (denser water) Wind-Driven circulation Air mass movement produces prevailing winds

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Sea Ice

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Sea ice l.jpg
Sea Ice

  • Reflects suns waves (energy)

  • Permanent on the poles (volume changes, but never completely melts

  • ~ 4m thick

  • Sea water freezes at ~2 ºC not 0 ºC

  • Leaves behind salts (denser water)


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Wind-Driven circulation

Air mass movement produces prevailing winds

Wind from the uneven heating of Earth’s Surface

Presence of land masses influences circulation

Energy & Motion of Oceans – Surface Waters


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Atmospheric

Circulation

Ocean

Surface Currents


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Surface Currents

  • Driven by atmospheric circulation.

Transfer heat from one place to another.

Keep the upper 100 meters of the ocean well mixed.



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Oceans and Climate

  • Q. Why is the climate in England mild even though it's at 55o N latitude?


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Oceans and Climate

  • A. The Gulf Stream current carries heat to Northern Europe.

Fig. 9.14


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Energy & Motion of Oceans – Deep Waters

  • Deep water circulation not influenced by wind

  • Density controlled by temperature and salinity

  • Cold dense water sinks at poles

  • Migrates slowly away, hugging the sea floor

  • Temperature and density difference allow for different currents to develop


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Global Circulation Patterns

  • Waters cycle between the different oceans.

  • One cycle takes 1000 years


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Thermohaline Current

  • Evaporation as current moves north, salinity (and density) increase.


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Thermohaline Current

  • Warm water loses heat to the atmosphere, density increases.


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temperature

Global climate change

atmospheric CO2

sea level


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Climate Change

Climate = average of weather conditions over seasons, years or decades

e.g. The climate of Illinois is "humid continental"

Depends on latitude, proximity to ocean, etc.

Climate changes over geologic time as continents drift and as Ice Ages come and go


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Studying Global Change

Geologic record: what happened in the past

Real-time monitoring: what is happening now

Mathematical models: predicting the future(also tested against the geologic record)


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What is a normal Earth Temperature?

"Snowball" Earth

Greenhouse Earth


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What is a normal Earth temperature?

Note we are actually way below average for the last 100 million years.

So why worry? 1) we were not around last time it was hot!

2) we are perturbing Earth systems much faster than most natural processes


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Temperatures: last 800,000 y

We are in an interglacial period; still have permanent ice caps (for the moment) so technically we are still in an Ice Age.


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Temperatures: last 150,000 y

Glacial-interglacial cycle is about 120,000 years

Now look at CO2 for the same period


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Temperatures: last 18,000 y

Glaciers retreated from upper midwest ~10,000 years ago

Last ~8,000 years have had relatively stable temperatures


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Temperatures: last 1,000 y

Vikings settled Greenland

Vikings abandoned Greenland


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Sea temperature in Medieval times estimated ~4 ˚C warmer than today

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Medieval warming period


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Temperatures: last 140 y than today

Not everywhere has the same temperature trend, but on average the planet's surface is heating up


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CO than today2 in the Atmosphere

Temperature during the Industrial Revolution

Link between CO2 and Global Temperature ?


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CO than today2 and climate

(Last 160,000 years).

Clearly the "Greenhouse Effect" is very real and acts on a short timescale

What about other greenhouse gases?


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The Greenhouse Effect than today

  • Greenhouse Gases

    • Carbon Dioxide (CO2)

    • Methane (CH4)

    • Nitrogen oxide (N2O)

    • Chlorofluorocarbons



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Carbon Cycle than today


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Greenhouse gases than today

Each greenhouse gas differs in its ability to absorb heat in the atmosphere.

HFC's and PFC's are most heat-absorbent.

Nitrous oxide traps ~ 270 times more heat per molecule than CO2; methane traps ~21 times more.


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Greenhouse gases than today

Greenhouse gases are global in their effect upon the atmosphere.

The main greenhouse gases have long residence times in the atmosphere, and therefore accumulate over time (unlike many local air pollutants)

Greenhouse gases are generally well mixed in the atmosphere, so their impact is mostly independent of where they were emitted.

Hence the emission of greenhouse gases should be addressed on a global (i.e., international) scale.



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Recent CO than today2 emissions

The US currently emits ~ 25% of anthropogenic CO2, mostly from burning fossil fuels

In 1990 the US emitted 5 billion tons of CO2 (~20 tons per person)


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CO than today2 emissions by country

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Some conclusions than today

  • "Naturally occurring" climate change has occurred in the paston many timescales, and will continue in the future. Several times in the past, Earth has been hotter or colder than today

  • Anthropogenic activities have greatly increased (and continue to increase) the concentration of greenhouse gases in the atmosphere

  • In the past, high levels of CO2 (greenhouse gas) have correlated with high temperatures

  • So we should expect global warming to continue in the future (noticeable on a human timescale)


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Title than today

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Future sea level rise (models) than today

Expect about 0.5 m in the next century.

Longer range predictions are less certain.


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