Mississauga Centre RASC

114th Meeting

                                                      Speaker’s Night  

           

 

Day:                Friday October 24, 2008

 

Speaker:          Vic Cooper

                     

 

The Astronomical Theory of Ice Ages

 

Vic Cooper is the treasurer of the Mississauga Centre RASC . He became interested in Ice Ages in High School when he asked what caused them and did not receive a satisfactory answer.  Subsequently, he studied the subject and became interested in cycles.  The first Ice Age or Epochs was the Proterozoic which began 800 million years ago (mya) and lasted 200 million years (my).  Subsequently, came the Ordovician (470 mya, lasting 50 my), Carboniferous (350 mya, lasting 100 my), and the Quaternary starting 3.6 mya and still ongoing.  During the last Ice Age, 29% of the Earth was covered by ice and the other part was largely a desert because so much water was tied up in the ice. 

 

Eccentricity, tilt, and precession are the three orbital elements determining the Earth’s tilt and distance from the Sun.  In 1797, Joseph Adhemar realized that energy falling on the Earth is slightly greater in one half of the orbit than the other and he said that ice ages are cyclical between the north and south hemispheres every 22,000 years Leverrier developed a formula for calculating eccentricity variations for the Earth’s orbit.  Using this, James Croll in 1821 realized that changes in eccentricity affected how much heat is distributed between the seasons.  Then, Milutin Milankovitch (born 1879), developed a theory of ice ages.  W. Kopper and A.Wagener took Milankovitch’s calculations and realized that the key was not was how cold the winters were, but how cold were the summers in the northern hemisphere.  The Earth is in a perpetual state of glaciation and there are interglacial periods as at the present time. 

 

Where do we find the proof of the theory?  Vic explained how the O18/O16 ratio varies in seawater in the ocean depending on evaporation and tying up of oxygen in land ice, and how the ocean cores with the ratios can be dated looking at reversals of the magnetic field.  Jim Hayes from Columbia University has studied cores from the Indian Ocean and showed that the cycle of 41,000 years is divided into 2 global periods of 22,000 years. 

 

The reason we are not in an Ice Age all the time is because of plate tectonics and sea currents. 65 Million years ago, Antarctica moved south, was isolated and surrounded by a cold current freezing the continent 35 mya.  In the north, the Americas came together blocking the E-W current, and land surrounded the north polar sea.  Warm water could not move north, and the isolated Arctic Ocean froze 2 mya.  This is probably the only time in earth’s history that both poles have been frozen at the same time. 

 

In the last glacial cycle there has been an interglacial period 125 thousand years ago when it was warmer than now with no ice at the north pole, and sea level 12 meters higher than now.  Earth warmed and then cooled rapidly.  In the last 20 thousand years, seas level has risen 130 meters.  The Holocene maximum was the warmest in human history and Earth’s tilt was greatest.  During the Mediaeval warm period from 1000 to 1400 AD, Vikings settled in Greenland and Canada. There were vineyards in northern Europe.  By 1400 it began to cool with the maximum coolest in 1680 – the Little Ice Age.  Winters during that time were extremely cold and long with a short growing season.  Glaciers advanced as winter snow would not fully melt.  Of note, the cool time was associated with the Maunder Minimum with no sunspots, and solar radiation was reduced.  Solar radiation varies due to changes in the Sun’s magnetic field and changes in orbital angular momentum in the solar system.  Various solar cycles go into and out of step presumable causing little ice ages. 

 

The Earth is bombarded by cosmic rays. During sunspot maximum, the flux decreases.  Isotopes C14, Be10 are reflected with little ice ages.  Low level cloud formation is the link between cosmic ray flux and solar irradiation.  Solar magnetism disrupts cosmic rays, less reach the Earth, less low clouds form and more solar irradiation reaches Earth’s surface (because there are less clouds to reflect the radiation away).  We don’t understand the link between the cosmic ray flux and low level cloud formation.  At CERN, CLOUD is an experiment in which Earth’s atmosphere will be bombarded by high speed protons to study such cloud formation.  

 

Ice Epochs are linked to astronomical cycles and plate tectonics.  Vic also discussed how climate change helped human evolution and civilization.   Many question ensued especially about how the current concern about global warming fit into the picture.    

 

 

 Submitted by Chris Malicki, Secretary  Chris Malicki, Secretary                               back to Miss Centre. meeting reports page
Mississauga Centre RASC