Ancient History
Ice-core, tree-ring and other paleontologic studies suggest that the warm temperatures that are being measured currently are unusual and have no precedent during the previous 1300 years.
The last time that the Polar Regions were warmer than the present temperature levels was more than 125,000 years ago. It is also noteworthy that, at that time, reductions in polar ice volumes resulted in a significant rise in the sea level and relocation of many coastlines from their present-day positions.
The earth went through a number of temperature excursions during its formative years over the past several hundred thousand years. Scientists (called paleoclimatologists) study this indirect historical climate record that Mother Nature has conveniently left behind for us to discover. Like crime scene investigators, scientists reconstruct historical climate conditions by examining evidence found in tree rings, by studying the layers of ocean sediment, and by analyzing the composition of layers taken from ice cores. The measurements were made at two separate sites in Antarctica-one at Vostok Station and the other at a separate location by the European Project for Ice Coring in Antarctica (EPICA). Both sites show that earth’s temperature has never deviated from a temperature range of roughly 10°C (18°F). We are currently about a degree or two above the midpoint of that range. This puts into perspective the nearly 1°C change that has already been determined for the past century with direct temperature measurements and the rate of increase that has been suggested by the trend in recent years. If the average global temperature continues to rise at the same rate as has occurred during the past decade, we may see climatic changes similar to those that have accompanied the retreat of past ice ages. Four additional ice age cycles moving through a similar temperature range and going back 650,000 years were obtained from ice-core data.
What is normal for the EARTH?
Temperatures have gone through natural cycles in the past. The medieval times were warm, followed by a cooler period from the seventeenth through the nineteenth centuries, after which a warming trend occurred. However, at no time during the past 11,600 years (the Holocene era in geologic time) have temperatures been as high as they are today.
Has global warming ever happened before?
The answer to this question is yes. However, before we take comfort in that thought, we should note that sea levels were most likely 4-6 m (13-20 feet) higher then than they are today.
Is this recent warming trend simply a phase that the earth is going through? Or is this something different? Looking back through the geologic records, we find periods of cold in the form of ice ages. These periods of cold alternated with interglacial warm periods. In some cases, the temperature records show that there were periods in history where the earth’s temperature was greater than it is today and greater than it would be if it continues to heat up at current rates.
