Past Climates & Climate Change

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  • 0:00 Paleoclimatology
  • 0:58 Ancient Climates
  • 2:15 The Holocene
  • 4:15 The Last Century
  • 5:39 Lesson Summary
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Lesson Transcript
Instructor: Christopher Muscato

Chris has a master's degree in history and teaches at the University of Northern Colorado.

Climate change is a big topic nowadays, but why? In this lesson, we are going to explore the changing climate throughout Earth's history and see why the current change is such a big deal.


Sometimes it seems like climate change is all we hear about these days. What does this actually mean? As of 2014, the average global temperature was roughly 60 degrees Fahrenheit, but actually even a slight change to this can have dramatic results. Over the last four billion years there have been dramatic shifts in the average global temperature from periods so cold that the polar ice caps extended almost to the equator to warm periods with tropical plants growing in Antarctica. The study of ancient climates is called paleoclimatology, and it's demonstrated that Earth's climate is constantly changing as a result of gasses in the atmosphere, cycles of the earth in relation to the sun, and other factors. So, what's the big deal if the climate is changing now? Well, let's take a quick trip through time and see what climate change is really all about.

Ancient Climates

Now like I said, the earth's climate is always changing, so we can't cover 4 billion years in our six minute tour. So, let's hit some highlights. From the beginning of Earth's history, we've got periods of extreme heat, some of extreme cold, but let's start here. Yep. That's a dinosaur. Welcome to the Cretaceous. It's about 70 million years ago, and the current global temperature is roughly 82 degrees Fahrenheit. Now, this doesn't mean that your average day will be a balmy 82, what this means is that the earth itself is radiating this much heat on average, so it is hot, humid, and muggy. Good for dinosaurs, not as great for mammals.

But, fast forward a bit and now we're in the Pleistocene, lasting from roughly 2.5 million to 11.5 thousand years ago. This period is also called the Ice Age by many. An extreme drop in temperatures to a global average peaking at highs of 42-51 degrees Fahrenheit led to a period of repeated cycles of glaciation, during which having fur turned out to be pretty advantageous, and mammals thrived. But, no dinosaurs. Starting to see why climate change can be a big deal?

The Holocene

And now, we get to the real reason we're out here. We are entering the Holocene, a geological period dating from roughly 11,500 years ago to present. While humans evolved in the late Pleistocene, the Holocene saw the first rise of civilizations. So, this is the period of human history. The Holocene has been an interesting period, marked by dramatic shifts in global temperature as a result mostly of our position in major cycles of solar radiation.

Researchers estimate that there have been as many as 20 climatic cycles during the Holocene so far, but they can be summarized in three major events. We start with a cool period roughly 11,500-10,000 years ago. New glaciers formed, trapping water as ice, and coastlines dropped, leading to massive migrations of animals and early people to places like Australia and North America. This wasn't the first major period of migration, or the last, but it was a big one.

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