According to the best scientific minds, the earth is 4.54 ± 0.05 billion years old. And since its beginning, the earth has experienced at least five major ice ages, i.e. the Huronian, Cryogenian, Andean-Saharan, Karoo Ice Age and the current Quaternary. In between ice ages, the earth appears to have been ice free -- even in high latitudes.
"Ice age" is a term that implies the presence of extensive ice sheets in the northern and southern hemispheres. By this definition, we are still in the ice age that began 2.6 million years ago because the Greenland, Arctic, and Antarctic ice sheets still exist. Therefore, the earth is still warming up from the most recent ice age -- and is expected to continue to warm until it is ice free.
There has been no satisfactory theory presented to explain earth's ice age history. The cause of an ice age is believed to be related to several simultaneously occurring ice-age-factors, i.e. astronomical cycles, atmospheric composition, plate tectonics, and/or ocean currents. Regardless, during the peak of the current ice age, the formation of 1.9 to 2.5 mile thick ice sheets caused a global sea level drop of about 390 ft. Therefore, while we may now be experiencing short-term volatility in our weather cycles, the expectation is that as in the past the earth will warm until it is once again ice free -- and the sea level has returned to its ice free level. Thus, if our historical science is correct, we are experiencing "natural" global warming as the earth warms out of its current ice age.
It is important we understand that the cycles from "maximum ice" to "ice free" and back are not linear transitions. In fact, they somewhat resemble the cycles of the stock market, e.g. short-term volatility within a long-term trend. For example, there is evidence that the "dark ages" were actually a reversion to a mini-ice-age due to a temporary variation in one or more of the identified ice-age factors, In addition, in June of 2011, scientists at the US National Solar Observatory (NSO) and US Air Force Research Laboratory announced that the Sun appears to be headed into a lengthy spell of low activity, which could mean that the earth -- far from facing a global warming problem -- is actually headed into another mini ice age, e.g. short-term volatility within the upward trend to an ice free earth.
So just what does this mean, i.e. what does an ice-free earth mean to mankind? Will it be the lifeless sweatbox the global-warming alarmists believe -- or will it be a lush Garden of Eden? In truth, we really do not know -- but earth's fossil history indicates that many forms of life survived the past ice ages in order to flourish during the ice-free periods. And it is an absolute truth that we have no control over earth's ice age cycles. So instead of exploiting the earth's normal warming trend by claiming global warming is man-made, perhaps it's time we acknowledged the situation for what it really is -- something over which we have no control -- other than to prepare for the future ice-free earth.