"Long, long ago, the planet Earth got warm: very, very warm." Is this the beginning of a fairy tale? Not really, but it is a fantastic story and still emerging from the pages of Earth's history.
Data show that about 56 million years ago our planet got very warm. This period is shown in the chart labeled Paleocene-Eocene Thermal Maximum. It is a bit of a mouthful, which is why the abbreviation PETM is mostly used.
The research is of major interest because the temperature spike was sudden and huge. The chart shows a large spike in temperature of about 5 degrees centigrade, or 9 degrees Fahrenheit, over earlier conditions.
Carbon dioxide levels also peaked (not shown), and the data suggests that the levels were perhaps four to five times that of today's. Sea levels were also far higher, and the polar ice caps were gone.
The obvious implication, and of interest to scientists, is the fact that we are combusting enormous amounts of carbon-based fossil fuels today, with a resultant 40-percent increase in atmospheric carbon dioxide levels, mostly in the past 100 years. An MIT study has estimated a doubling of today's levels by 2100, under a "business as usual" scenario, or about half the PETM levels.
So what was going on? Humans cannot be blamed for that event, as we were not even a twinkle in nature's eye then.
Enter Paleoclimatology. This relatively new discipline is the study of past climates. This sounds straight forward, but the challenges of understanding events millions of years ago are formidable. Determined scientists have, however, developed new tools and techniques, and with lots of field work, found rock layers and ocean cores that span that time period. This has given us a good glimpse of what happened back then.