I'm going to give you a shocking, disturbing answer that many will find disgusting and will force me to repent for my sins.
We don't know enough about how the climate works.
Edit: Sorry, I guess that wasn't a good enough answer so I'll try to explain what I think I know which may or may not be correct. First thing, it is important to note that most of the Earth's land mass is in the northern hemisphere. Second thing to note is that the periodicity of ice ages is about 100,000 years which correlates well to one the orbital eccentricity cycles described by Milankovitch.
Currently, the Earth is closest to the Sun in January which is near the beginning/middle of winter. The Earth travels faster in its orbit at this time and thus our summers are actually longer than our winters. As this changes, there will be a point where we are closest to the Sun in the summer in which case our winters will be longer than our summers. This may result in snow having less time to melt and thus it can accumulate.
It's obviously much more complicated than that and likely many factors add up which cause a net accumulation of ice and snow over hundreds and thousands of years to put us into ice ages and keep us there until the net accumulation reverses to the extent that we enter an interglacial period.
And like I said, we still don't know exactly what causes ices to begin or to end. We suspect they are related to Milankovitch cycles and certain points of these cycles make conditions right for starting or ending an ice age but we don't know the rest of the mechanisms.
Perhaps it was cloudy so no sun. Nice tutorial Mike, keep it up.
There comes a point when ice creates so much negative feedback that it prevents enough solar radiation from being absorbed to warm up the climate enough to ment the ice. In other words there was enough surface ice to reflect most solar radiation back out into space during the day and at night release thermal energy that may have been absorbed during the day. Colder climates reduce the rate of evaporation from the oceans which mean less clouds to act as a blanket.
Here is an article that discusses that earth was once in such a deep ice age that ice extended clear down into the equatorial regions. Volcanic activity under the oceans is what saved the planet from being permanently frozen.
http://news.nationalgeographic.com/news/...
Well were still in the end of an ice-age and the suns doing a good job of melting it now.
well a major ice age occured so long ago that our sun was not producing enough energy and the slightly lower sunlight was blocked by volcanic ash and reflected by the ice sheets which do reflect up to 70% of sunlight. the atmosphere collects less than 1% of very shortwave white sunlights heat energy but the 99% is easily collected by earth and rock which radiates the heat back in long wave radiation the air easily absorbs, if the ice reflected it back in its shortwave form then its heating effect was lost and the earth stayed cool. our sun is growing into a red giant star very slowly and getting nearer to earth at a snails pace, in 2 billion years it will stop just shy of our moon and be so hot all the beachsand will be melted to glass everywhere!
If it wasn't for global warming -- Chicago would still be under a mile of ice.
Fortunately, Cro Magnon people learned how to make fire and the smoke from their campsites melted the glaciers.
We had a much stronger ozone layer back then, and the earth was a few miles farther away from the sun.
On top of that the tilt of the earth was slightly different with the spin leaning downward. that means at any given time there were certain places on earth that were facing away from the sun.
Maybe it did.
The simple answer is that during an Ice Age, the summer Sun does not melt all of the snow from the previous winter, allowing snow and ice to accumulate. Snow and ice is highly reflective and this tends to keep the planet cold.
The Earth's orbit is not perfectly circular, but is elliptical. It also wobbles on it's axis, a bit like a spinning top. Minor changes to these motions happen in cycles of tens of thousands of years; these are known as Milankovitch Cycles. It is the combination of these changes that results in a cycle of ice ages and warmer periods such as we are in now. It has nothing to do with the Sun itself; solar output is virtually constant.
The basics are all here, let me know if there is anything you want explaining and I'll do my best to help.
http://en.wikipedia.org/wiki/Ice_age
http://en.wikipedia.org/wiki/Ice_age#Var...
The Ice ages were caused by a cooling climate, that simply means it wasn't warm enough to melt the ice. we have ice caps and glaciers now and the sun only melts them a little and they freeze back in winter.
In the ice age how come the sun did not melt it .
