Fire and Ice - Global Warming and Ice Ages

1. Terrestrial Weather is Sun Driven

Blue Sky = blue sunlight scattered by air molecules
Water cycle = Evaporate sea water with sunlight, clouds, wind, rain
Global weather = redistribute solar heat across globe by winds and air currents

Seasons = annual change in the amount of incident sunlight due to tip of hemisphere toward Sun (summer) or away from Sun (winter) - part of yearly orbit of Earth around Sun.


2. Unnatural Warming of Earth with Man-made Carbon Dioxide

Global surface temperature seems to increase over past century, but moves up and down as much - large natural fluctuations

Carbon dioxide content of our atmosphere increases exponentially during past century - right now at the rate of one ton CO2 per person every year - due to factories and cars - should heat Earth by greenhouse effect.

Other heat trapping gases contribute about half the heating - also by greenhouse effect - methane, CFCs, nitrous oxide.

Predictions of unnatural greenhouse warming limited - oceans and trees absorb CO2, sulfur in air cools Earth, clouds can cool or heat.
Clouds keep sunlight from reaching ground but also trap heat near ground.


3. Sun heat Earth

Solar radiation is variable by 0.1 percent (see last chapter) produces 0.2 degrees Celius temperature change at Earth.

Much greater temperature change at higher altitute during solar activity cycle.
For now, solar cycle length is correlated with global temperature - shorter Sun activity cycle = more intense solar activity = hotter temperature at Earth.

But, global warming by man will eventually outstrip Sun warming (or cooling) effect.


4. Global Warming can be Bad and Good

Oceans rise and flood coastal cities - warm water expands (like thermometer) But note melting ice caps do not change ocean level (water world is wrong)
More power needed for air conditioners.
But, you don't have to shovel snow and the temperature change isn't bad. Greater temperature difference from New York City to Florida, from Paris to Naples, or from winter to summer.

Crops and forests change.


5. World Politics and Global Warming from Man-made CO2

Industrial countries agree to limit carbon dioxide, or CO2, production by 2000 to 1990 values.
Developing countri es like China do not want to curtail their industrial growth by limiting CO2.
(Note: United States makes 18% of CO2, and most CO2 comes from Northern hemisphere.)
Compromise - economic growth without damaging environment.
Even in industrialised countries, environmentalists predict catastrophy from rising CO2 and temperature; but industries say natural temperature fluctuations are greater than CO2 ones so far.


6. Astronomical Causes of Ice Ages

A. Major Ice Ages
In major ice ages glaciers cover much of northern hemisphere, temperatures drop by about 8 degrees Celsius. Glacial ice lasts 100,000 years. Warmer interglacials last 10,000 years. (note: we are now near end of interglacial)

Milankovich cycles - astronomical rhythms cause ice ages

All produce Rotational wobble = 23,000 year
variation in amount of Axial tilt = 41,000 years
sunlight incident on Orbit shape = 100,000 years
Earth

Note: Ice cores show temperature goes up when CO2 does, but we do not know how they are related e.g. maybe hotter times create more CO2 or vica versa.


B. Minor Ice Ages
May be caused by dramatic variation in solar actitivity ( a large decrease) over time scales of centuries. Glaciers advance, rivers freeze, crops fail.

Example = little ice age, 1500 to 1800
No sunspots or auroras
1400-1500 and ~ 1700 (Maunder Minimum)

You can get an ice age if total radiative output of Sun decreases by 0.2 to 0.5 percent - more than present 0.1 percent variation over 11 year activity cycle. Other stars exhibit this greater variation suggesting Sun might do so on century time scales.

Robert Frost
Some say the world will end in fire,
Some say in ice.
From what I've tasted of desire
I hold with those who favor fire.
But if it had to perish twice,
I think I know enough of hate
To say that for destruction ice
is also great and would suffice.

Dalai Lama - September 1996
We believe the world will come and disappear - so eventually the world becomes desert and even the ocean dries up. But then again, another new world is reborn. It's endless.