There are a variety of truly natural oscillations in our planet’s orbital journey that lead to periodic variations in global weather or climate Change. We can observe these true “natural variations” in different geological records. In fact, this year and for the near future, we should be experiencing a downward cooling trend in temperatures instead of the relentless upward trends caused by anthropogenic warming. Let’s take a look at global conditions during the last “Glacial Maximum” period which lasted from 23,000 years ago to 19,000 years ago. Yes, these natural variations last a long time compared to the span of a human lifetime, but from a geological perspective, such cycles and eras are the blink of an eye.
Temperature – Through measurements and modeling, the global average temperature was about 13 degrees Fahrenheit cooler than 2019. Some regions experienced greater cooling while other regions had less cooling. Polar regions were about 25 degrees F cooler than 2019. Tropical regions cooled less than the average.
But we are talking about the last “Ice Age” which lasted much longer than the Glacial Maximum signaling the end of the age. The Ice Age itself (this most recent one) lasted from 1115,000 years ago until about 11,000 years! By carefully measuring the ratios of oxygen isotopes in tiny bubbles trapped in ice cores, scientists have been able to model average global temperatures going back even earlier to 650,000 years ago. Just looking at this last ice age, in an 80,000-year period, there were twenty-five cycles of warming and cooling called Dansgaard-Oeschger cycles, or D-O cycles.
Those twenty-five cycles lasted a few centuries each time with temperatures increasing or decreasing ten to fifteen degrees from the long-term average. As mentioned earlier, our planet should be experiencing a downward trend in temperature because of the D-O cycle which makes the actual warming trend even more alarming. But what was it like during that last ice age and how did it end?
Ice sheets up to a mile high, covered most of North America down to about the Missouri River in central Missouri. Large animals well adapted to a cold climate such as the mammoths, mastodons, woolly rhinos and saber-toothed cats roamed the landscape. Sea level was about 400 feet lower than today because so much water was locked up in ice. The average global temperature was about 46 degrees Fahrenheit. An ice and land bridge existed across today’s Aleutian Islands at the Bering Sea. Nomadic bands of humans could cross from Asia to North America and travel down an ice-free interior valley in Alaska. The large animals in North America may have been hunted to extinction by the incoming human population.
There is physical evidence indicating that during the warming phase of the D-O cycle, monster hurricanes pounded the coasts. In the ice-free equatorial regions, there was long-term drought due to the lack of moisture. Today’s tropical rainforests were deserts then. Ironically, Siberia was ice free because the intense “anti-cyclones” produced by Europe’s ice cover sent steady high winds across Siberia with no moisture to produce an ice pack. In another irony, heavy rainfall in regions of North America that are desert today produced pluvial lakes such as Lake Bonneville. Equatorial Amazon and African rainforests that were not desert were savannah or grasslands. It was a crazy world back then. Winter clothes would be needed year-round in Florida.
The original human inhabitants of North America who descended from nomadic migrations over five-thousand years prior were forced to live closer together in “refugia” or ice-free regions south of the glaciers. We can see these genetic trends of “haplogroups” in today’s population of Native Americans. Human life then was most likely “nasty, brutish and short.”
How did the last ice age and the Glacial Maximum end? Short answer, abruptly. Several natural cycles of weather drivers aided perhaps by volcanic eruptions led to a rapid conclusion, in less than a century. Ice sheets retreated into Canada moving several feet per day. Glacial runoff into the Mississippi River basin formed a massive waterfall thousands of feet high that cut through the continental plate of granite several thousand feet below the surface. Winds died down and the atmosphere was less dusty. The Great Lakes were carved as the glaciers’ retreating swan song. Native Americans dispersed across the continent forming distinct linguistic and genetic groups. Temperature warmed by ten to fifteen degrees Fahrenheit. Life was good again.
It is true that the planet has experienced warming trends with alligators and tropical fern trees in the arctic and Antarctic. But it is also true that every time a warming trend has occurred coupled with rapid rise in atmospheric CO2, there has been an associated rapid decline in species by as much as 90%. And each time this occurs, it takes the planet tens of thousands of years to get the temperature back to a habitable level where diverse life can flourish again.
We don’t have the time or space here to rebut all the climate-change denier arguments. But if you think natural variations are significant, then you need to explain why the natural cycles and variations would all lead to a cooling trend today instead of the warming we observe. What I would hate to see is another 100,000-year cycle where only 10% of today’s species make it to the other side. Some bi-pedal hominid species grad student would look at the fossil record and think to themselves, “Silly buggers. They just burned themselves up while they argued about it.”