Earth has been going through warming and cooling trends for at least the last million years according to paleo data. We even have historical records for cycles within the past thousand years or so, such as the Medieval Warm Period (900-1300 AD) and the Little Ice Age (1450-1900 AD). And, none of these trends were based on humanity but on natural cycles and events.
How Do Scientists Figure Out Ancient Temperatures and Climates?
There are at present many different ways that scientists can figure out what ancient temperatures were, and what the climate was like in any particular region anywhere around the planet.
For example, I come from the American Midwest. Below us, as our bedrock, is a large layer of limestone. Our gravel used for gravel roads and the making of concrete comes from this limestone. It tends to be white, off-white, or grey in color, and is composed primarily of calcium carbonate. The kind of limestone that we have makes it clear to geologists that much of the Midwest was a shallow, inland sea many millions of years ago, and this inland sea was covered by thousands of square miles of coral, as well as other marine creatures that had shells made of calcium carbonate. Since this layer of rock would have grown very slowly over long periods of time, it makes it clear that the climate and environment of the American Midwest was very different than it is today. This is just one example of how geology can determine the different environments and climates of a geographic region over the course of time, and geology is just one of many different sciences that can be used for determining how climates and environments can change over time.
Back to the marine organisms and shells of coral I spoke of in the last paragraph – not only were they useful for the making of limestone over a long period of time, but they can also be preserved in the limestone as fossils. And as fossils, they are one of a multitude of examples of the types of fossils that can be preserved in rock, and these fossils all tell a tale of what kind of climate a locale had millions of years ago. In the case of these marine fossils in the middle of the North American continent, it shows that the region, now an above-water part of a continent, used to be wet, as it was underwater. Another example are the fossils of palm trees and crocodiles that they’ve found in the Arctic regions of northern Canada and Siberia in Russia, which shows that these regions, at one time in the distant past, were much, much warmer than they are now.
Another way that scientists can determine climate and temperature is to look at ice samples in the ice sheets that cover Greenland and Antarctica. Or they can look at marine sediments on the ocean floors. Both of these can uncover how much carbon dioxide was in the air at any particular time in the distant past, as well as what the temperatures were like at that time.
There are many other things they might look for, too, which can give them clues as to the temperature and climate besides the amount of carbon dioxide in the atmosphere: the amount of water vapor in the air, the amount of cloud cover, the amount of land covered by ice and snow, the percentage of earth’s land that were covered with forests, and how much of the earth’s surface was covered by oceans and seas – all of these can have an effect on the earth’s temperature and climate.
Oh, and all those things can have an impact on rainfall, wind patterns, and ocean currents (ocean currents can also be impacted by movement of tectonic plates which can change positions of the continents on the planet over time).
Back to Warming and Cooling Cycles
Now this is where we get back to the statement at the beginning of this article: that there has been variability in the earth’s temperature for the last several million years, all before we humans came along, established our modern industrial age, and had our own impact on the world’s climate and temperatures.
For example, we know that there have been several ice ages in the past, where the earth was much colder than it is now. We know that there were times where the earth was much warmer, as, like I’ve said, there is evidence of palm trees and crocodiles in areas that are today’s frigid Arctic climate.
We know that there were times that the earth’s sea levels were much higher than they are now – up to 200 feet higher. At other times, sea levels were up to 400 feet lower than they are now, exposing most of the earth’s continental shelves, which were at those times above water. They’ve even found remains of land creatures in the continental shelves off the costs of North Carolina, as well as the Grand Banks off the coast of Canada’s Newfoundland.
We also know that the level of carbon dioxide in the atmosphere has varied considerably over time. When the earth was very warm, the level of carbon dioxide in the atmosphere has been estimated to be between 600 and 1400 parts per million (ppm). At one point in the very distant past, the Cambrian period, the level was an extremely high 4,000 ppm. At the end of the last ice age, the level was about 280 ppm. Right now, we have about 415 ppm, with levels increasing about 2.6 ppm per year due to human-caused releases.
On a side note: concerning the formation of the Antarctic ice sheet, current modeling suggests that carbon dioxide levels lowering from higher levels to about 780 ppm provided the threshold for the Antarctic ice sheet to start forming long ago. At our present rate of increase, we will increase to that amount by around 2150 AD
Conclusion
So, when we talk about human-made impact on the climate, we need to realize that cycles of the earth warming up and cooling off have been going on for hundreds of millions of years. And we humans were not a part of it. These cycles will continue, with or without us humans being part of the equation.
With that being said, there is the other side of the equation, explained in my article The Big Non-Correlation Between Earth’s Warming and Cooling Cycles and Today’s Carbon Dioxide Levels.
