I have been studying the science of global warming with a passion since the late 1970s and earned a degree in Environmental Science in 1992.
We are currently living in an interglacial warm period that started approximately 12,000 years ago when the last minor glacial ice age ended and huge ice sheets started retreating towards the poles. It is hard to imagine, but going back billions of years scientists studying the geologic history of the Earth have found at least two periods of time during which the Earth was completely or nearly completely covered in ice or a slushy mixture of ice and water, which is known as “Snowball Earth.” On the other end of the spectrum, the geologic record indicates that Earth has been completely or nearly completely ice-free several times in the past, which is known as “Greenhouse Earth.”
Why Earth's Climate Has Been Radically Colder and Warmer in the Past
Natural forces that vary over time, such as the sun's intensity and distance from the Earth, impacts from asteroids, volcanic activity, biological impacts, the concentration of greenhouse gasses in the Earth’s atmosphere, and natural climate feedback loops have caused the Earth's atmosphere to cool and warm significantly in the past per the geologic record. Essentially, once Earth’s climate started moving in one direction or another (colder or warmer), when the conditions were intact to support the trend, climate kept moving in either a colder or warmer direction until extremely cold or warm climate conditions prevailed. The climate state would only be reversed once the underlying climate drivers of the process changed to a great enough extent to reverse the prevailing temperature trend and return the Earth's climate to a more moderate range.
We are living during a time of rapid global temperature warming that the majority of scientists attribute to human activities. Given our current predicament, it is fascinating to look back at periods of extreme cold and heat in the Earth's past to understand just how extreme the Earth's climate can actually get once it starts moving in one direction or another. This look back also helps answer the question of whether mankind really can collectively affect something as vast and powerful as the Earth’s climate and global temperatures.
What Snowball Earth Probably Looked Like From Space
Snowball Earth: When Earth's Surface Was Either Entirely or Nearly Entirely Covered in Ice
One of the mysteries about the incredibly cold Snowball Earth periods in Earth's history is how life in any form was able to survive. The best theory scientists came up with is that either area of ocean near the equator was ice-free and exposed to the sun or the ice near the equator was thin enough to allow sunlight through so that microbes could survive.
The video below is a fascinating look at the natural forces that led to Snowball Earth and what the Earth looked like when it was covered with ice.
How Snowball Earth Happened
Earth From Space With No Ice Caps
Greenhouse Earth: When Earth's Surface Was Ice Free and Warm All The Way To The Poles
In direct contrast to Snowball Earth, scientists studying the history of Earth's climate have uncovered periods of time when the Earth's surface was nearly or entirely free of ice. These excessively warm time periods are nicknamed Greenhouse Earth since Earth was very warm like a greenhouse on a sunny day. During these times, Earth's atmosphere was so warm that little or no ice existed in either the North or South polar regions. In fact, the fossil record indicates that plants associated with lush green forests existed in northern regions of Canada and parts of Greenland.
The video below takes you on a fascinating journey that explains the natural forces that led to Greenhouse Earth and what the Earth looked like when it was free of ice and warm all the way to the poles.
The Last Time the Globe Warmed - Greenhouse Earth
What Past Climate Extremes Tell Us About Current Global Warming
What does this look back at climate extremes tell us about our current global warming predicament in which Earth's average global temperature is warming at an extremely fast pace compared to past warm-ups that were driven by natural forces? It tells us that the current rate of warming is unprecedented in comparison to the geologic records, which is an indication that mankind's activities, rather than natural forces, are causing this rapid warming. It also tells us we may eventually have to prepare for a much warmer Earth in the not too distant future since once climate starts moving in one direction positive feedback loops can cause Earth's climate to reach extremes until something eventually changes the trend to a new direction. Finally, it tells us that biological forces such as microbes and plants have had major impacts on Earth's climate in the past, which supports the scientific agreement that mankind's activities are capable of having major impacts on Earth's climate now and in the future.
We Are Technically Living In a Long-term Ice Age Right Now
As odd as it may sound since we are living at a time when the Earth's atmosphere is warming considerably, we are technically living within a long-term ice age called the Quaternary glaciation that started 2.58 million years ago. The scientific community considers any time that Earth has a significant amount ice in the arctic region to technically be an ice age. When Earth is not in a long-term ice age, there is little or no ice in and around the Arctic and the Antarctic north and south poles, a condition that has occurred several times during Earth's history according to the geologic record. If global warming plays itself out to its full possible extent in a not too distant future century, the Earth may warm enough to melt most or all of the ice in the polar regions and will once again be a Greenhouse Earth.
A Depiction of How Earth Has Warmed In Recent Years
Earth's Climate Direction Poll
© 2019 John Coviello