Earth has been ice-free before, just not (probably) since humans have inhabited it. I always told my children that those dang dinosaurs and their coal-fired power plants and SUVs were responsible. There used to be a very nice display in the Beringia Museum near Whitehorse, Yukon, that explained past climate changes very well, but it may not exist any more since it wouldn't fit into the current man-caused-climate-change fad that is controlling things. The museum display explained that the earth has been slowly warming for the last 15,000 years (since the last Ice Age) and has cycled this way for eons--since before life appeared on this planet.
@Don Alaska I've been longing to hear things stated that way for quite some time now. While I do not doubt broad swings of climate have occurred time and again, at the same time I consider that during those eons enormous amounts of fossil fuel were not being burned. Does this mean those quintillions of BTUs thrown into the atmosphere annually are inconsequential given the broadness of scope of the entire Earth? Frank
The BTUs sent into the atmosphere are significant, but nowhere near those contributed by the sun. There appear to be cycles of dramatic shifts in temperature and precipitation that last millions of years. Smaller shifts last decades or centuries. I think most of the climate alarms are about profits and control. Some of the claims may be valid, but it is almost impossible to sort the valid claims from the BS. One of the biggest contributors to "carbon emissions" is the commercial airline industry. No one even mentions that, as the advocates like to fly too much and often use private jet aircraft--the worst of all--to fly to the Climate Change meetings. I have known commercial greenhouse operators who deliberately pipe CO2 into their greenhouses to accelerate plant growth. Increased CO2 in the atmosphere should make the rainforests flourish. The oceans seem to be warming, but that could be from undersea volcanic activity such as the large volcano discovered a few years ago off the north coast of Greenland or magma movement beneath the ocean floor. Magma movement may be one of the causes of ice ages. I read a book by a well-known biologist in Oregon, who said when investigating global warming, plugged the known parameters preceding the Little Ice Age into the current algorithms predicting global warming to see what the result would be. The algorithms predicted increased temperature rise for decades when it fact the global temperature dropped dramatically and changed human culture throughout Europe (at least).