The one thing that can be said about the earth's climate is that it's always changing!! There are many factors that control the climate. The system is what we call a complex system. This means that a small change in some input such as the luminosity of the sun can cause a major shift. One way to think about the climate system is to envision a system that is dynamically unstable but at a quasi equilibrium...imagine a ball at the very top of a slope such that at any location around where the ball is resting is downhill..... Now if no perturbation occurs, then the ball stays at equilibrium and does not move... now imagine a butterfly cruises by....the effect of the slight wind is to give the little ball a little push!! it is a VERY VERY VERY small push... but it is enough to get the ball moving...and as soon as the ball moves a tiny amount, it is going downhill... and as it goes down, it now picks up momentum due the gravity... the ball rolls all the way down the hill.... and ends up 100's of yards from where it started... now if you think about it, that little butterfly did this!!!??? Well, yes and no... the butterfly was the tiny PERTURBATION that allowed the ball to seek a new minimum energy configuration in the gravitational field of the earth....

So this is just an analogy ... the idea is that small perturbations can produce drastic changes when one deals with a complex system of which climate on any planet but especially earth is an ARCHTYPICAL example.

The quaternary ice ages seem to correlate with the amount of solar energy the earth gets... it is a little variable because the earth wobbles on its axis and its axis also processes... and the eccentricity of the earth's orbit around the sun changes a little bit... this is called ASTRONOMICAL FORCING and ice ages are related to that in large part.

Another type of forcing has to do with the composition of the air.... methane and carbon dioxide are good trappers of IR radiation... so when visible NOT IR radiation from the sun heats the earth surface, some of that energy is re- radiated in the IR part of the spectrum... now THAT IR energy is absorbed by methane and CO₂ and hence is trapped by the earth.....

The concentration of CO₂ has gone up significantly since the industrial revolution. Complicated models of the earth atmosphere that have been developed by advanced scientists over the past 80 yearsrs with increasing sophistication show that as the CO₂ content increases, temperature average of air will go up.

So to summarize...climate is a complex system and reducing a complex system to a linear one is a big mistake....but having said that, the current heating of earth especially in 20 and 21 century is very likely due in significant amount to CO₂.

First, the Great Lakes were formed from ice bergs that scoured out the land during one of the ice ages.The glaciers went as far south as Nebraska. As far as ice melting being due to human caused global warming that is hard to prove. If you look at geologic history, the earth has gone through numerous climate changes over the past couple billion years. There have been times when the earth was completely snow/ice covered (Snowball Earth) and there have been times when the earth was almost ice free. When the dinosaurs were around, the global average temperature was about 80degF, compared to today's approximate 44degF. So the big question comes back to the thought that humans have caused a rapid climate change. Or is the earth within a rapid period of climate change. I am not sure that that direct correlation is easy to prove or disprove. What can be said is that humans have increased the amount of greenhouse gases in the atmosphere, but can it also be said that those greenhouse gases have actually been a factor in climate change.Good question and you can find numerous scientists on both sides of the issues with valid arguments.