- ~3 Million Years Ago (Ma): A significant transition to colder conditions began, leading to the initial formation of the large ice sheet.
- ~2.7 Ma: Ancient tundra soil was preserved beneath the ice, indicating an ice-free landscape existed before this time, followed by ice sheet growth.
- ~2.5 Ma: Evidence points to even more widespread glaciation.
- ~1 Million Years Ago (Ma): The oldest ice still present today dates from this period, but there were also times of significant melting before this.
- ~400,000 Years Ago (ka): Evidence suggests much of Greenland was ice-free, with tundra ecosystems thriving, even with CO2 levels lower than today.
This is the problem with a lot of people who do not really understand science. And even the terms can be a bit confusing.
We are at the tail end of the Wisconsin Ice Age, which is simply a phase of the Quaternary Glaciation. And even among experts, the use of "Glaciation" and "Ice Age" is almost interchangeable. In general, the phases tend to run roughly around 100,000 years for a glacial cycle, then around 30,000 years for an interglacial. Then things start to get colder again and another ice age starts.
Now in the above chart, the top level is Greenland Ice Core Data, the bottom is Antarctic Ice Cores. And the reason it is more obvious in Greenland is because almost all of the glaciation happens in the Northern Hemisphere, because there ocean coverage is only 60% compared to over 80% of the Southern Hemisphere.
But even only going back 58 kya, the cycles are obvious. And it must be remembered, every one of those variances has occurred either during the Wisconsan Ice Age or in the Holocene Interglacial. When examining the above chart, one must absolutely be aware that pretty much everything to the right of GI-4 is during our current interglacial.
And every single fluctuation to the left actually occurred during an ice age.
This is because this chart only goes back 58 ky, and the last ice age started at roughly 120 kya. This is not even a chart of ice age cycles themselves, but of climate changes and fluctuations during the last third of the last ice age, and the start of the current interglacial.
Original source if any are interested.
