What can we learn about the near future on Earth by looking back at eons gone by? Quite a lot, according to scientists from the U.S. Geological Survey (USGS).
The time period to look at most closely is the Pliocene era, roughly three million years ago. At that time, the world probably looked and felt much as it does now, and global temperatures and the amount of heat-trapping carbon dioxide in the atmosphere were similar to what we have today.
The big difference, of course, is that homo sapiens was not yet on the scene – and certainly not yet contributing to the amount of CO2 gas in the atmosphere.
Using sophisticated new techniques (like comparing atomic weights of isotopes from samples in sediment layers), they’ve figured out a lot about what was going on around the planet in that era of warming. The results are published in the journal Nature Climate Change.
A summary of their findings by Reuters News, explains it thusly:
The mid-Pliocene was about as warm as climate models predict it will be by 2100, or about 3.6 degrees Fahrenheit above current global mean temperatures.
Sea levels were as much as 70 feet higher than they are now. Florida would have been a narrow strip instead of a broad peninsula, Washington, D.C., might have offered oceanfront views and much of Bangladesh would have been under water. Greenland, now covered in melting glaciers, had forests growing on its northern slope.
Animals and plants would have looked familiar to 21st century eyes, as newly formed grasslands attracted long-legged grazers. The dinosaurs were long gone, and the mountains were basically built. Two-footed ancestors of homo sapiens probably walked the Earth.
Carbon dioxide levels in the atmosphere were between 350 and 400 parts per million (that is, between 350 and 400 carbon dioxide molecules for every million molecules of air), said Mark Pagani, a pale climatologist at Yale University, who called the estimates “a pretty good ballpark figure.”
The figure of 350 parts per million of CO2 in the atmosphere represents the upper safety limit before a runaway effect is set in motion. And in March of this year, we were approaching the 400 mark.
The scientists point to what is happening today as a super-accelerated version of what was taking place three million years. They show the rate of warming in this graph from the USGS:
So we can we expect in our own “neo-Pliocene” age? Obviously, things are not the same today as they were then. But although what happened three million years ago was cause by natural effects, what’s happening today is being seriously amplified by human hands, and all the warning signs are in place.
Once changes have been set in motion, the effects tend to unfold over a very long time. Humans have been putting additional carbon dioxide into the atmosphere through the burning of fossil fuels for only a century or so. And what we’re seeing now is just the beginning of what happens after excess carbon dioxide gets into the air and the full warming effects are felt.
So, should we expect sea levels 70 feet higher than they are now? We don’t know. But can we afford to continue the way we are? Probably not.