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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Transfer heat from one place to another.
Keep the upper 100 meters of the ocean well mixed.
Global 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
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)
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
We are in an interglacial period; still have permanent ice caps (for the moment) so technically we are still in an Ice Age.
Glacial-interglacial cycle is about 120,000 years
Now look at CO2 for the same period
Glaciers retreated from upper midwest ~10,000 years ago
Last ~8,000 years have had relatively stable temperatures
Vikings settled Greenland
Vikings abandoned Greenland
Medieval warming period
Not everywhere has the same temperature trend, but on average the planet's surface is heating up
(Last 160,000 years).
Clearly the "Greenhouse Effect" is very real and acts on a short timescale
What about other greenhouse gases?
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.
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.
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)
Expect about 0.5 m in the next century.
Longer range predictions are less certain.