THE MAJOR ICE AGES ON EARTH AND MAJOR GLOBAL WARMING EVENTS

• Fenced at least five major ice ages throughout its 4.5-billion-year history. An “ice age” refers to a long interval (millions of years) during which global temperatures are cold enough for permanent ice sheets to exist.
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• Major Ice Ages in Earth’s History
• Hurrian Ice Age (2.4 – 2.1 billion years ago): The oldest known ice age, potentially the first “Snowball Earth” where the entire planet froze.
• Cryogenian Ice Age (720 – 630 million years ago): Likely the most severe; ice sheets may have reached the equator.
• Andean-Saharan Ice Age (460 – 420 million years ago): Occurred during the Late Ordovician and Silurian periods, coinciding with a mass extinction.
• Kazoo Ice Age (360 – 260 million years ago): Named after glacial tills in South Africa, this period saw extensive ice cover across the ancient supercontinent Gondwanaland.
• Quaternary Ice Age (2.6 million years ago – Present): Technically, Earth is currently in an ice age because ice sheets still exist in Antarctica and Greenland.
• Glacial and Interglacial Periods
• Within an ice age, the climate fluctuates between “glacial” (colder periods of ice advance) and “interglacials” (warmer periods of ice retreat).
• Last Glacial Period: Colloquially known as “The Ice Age,” it began approximately 115,000 years ago and ended 11,700 years ago.
• Last Glacial Maximum (LGM): The peak of the previous cold period, occurring roughly 26,000 to 20,000 years ago.
• Holocene Epoch: The current warm interglacial period, which began about 11,700 years ago and continues through 2025.
• Little Ice Age (c. 1300 – 1850 AD): A more recent, smaller cooling event that primarily affected the Northern Hemisphere.
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1. Bcc. 2600000 BCE — c. 12000 BCE
2. The Pleistocene epoch, ranging from c. 2.6 million years ago until c. 12,000 years ago. It is characterized by repeated cycles of glacial and interglacials.
3. c. 26500 BCE — c. 19000 BCE
4. Last Glacial Maximum — the time during which the ice sheets reached peak growth within the most recent glacial period.
5. c. 11700 BCE
6. End of the most recent glacial episode within the current Quaternary Ice Age.
7. 1837 CE

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Difference from the historic average temperature since the last ice age. NOAA Climate.gov cartoon by Emily Greenhall. Inspired by Figure 1(b) in

• This article is the second of two articles describing the hottest time periods in Earth’s history. Since this article was first published in 2013, additional research has concluded that current global temperatures are more likely to be the highest seen on Earth since the last interglacial period 125,000 years ago. (See the IPCC Sixth Assessment Report, Technical Summary, page 61, and Kaufman and McKay, 2022, “Technical Note: Past and future warming – direct comparison on multi-century timescales.”
• Throughout its 4.54-billion-year history, Earth has experienced multiple periods of temperatures hotter than today’s. But as far as the “recent” past, a study published in March 2013 concluded that the global average temperature is now higher than it has been for most of the last 11,300 years.
• The scientists assembled dozens of temperature records from multiple studies, including data from sediment cores drilled into lake bottoms and sea floors, as well as ice cores. Assembling data from 73 overlapping records, the scientists pieced together global average temperatures since the end of the last ice age.

A researcher examines an ice core extracted from the West Antarctic Ice Sheet—photo courtesy.

• The 11,000-year temperature reconstruction shows that the global average temperature increased after the last ice age and leveled off around 7550 and 3550 BC. After that time, global temperatures dropped until the “Little Ice Age,” bottoming out somewhere between AD 1450 and 1850. Afterward, temperatures rose again, first slowly, then rapidly. (The estimated temperatures for the past 1,500 years correlated with previous research that covered the same time period.)

1. Global temperature anomalies over the past 11,300 years compared to the historic average (1961-1990). The purple line shows the annual anomaly, and the light blue band shows the statistical uncertainty (one standard deviation). The gray line shows temperature from a separate analysis spanning the past 1,500 years. Image adapted.

• Natural variability can explain much of the temperature variation since the end of the last ice age, driven by factors such as changes in Earth’s axial tilt. Over the past century, though, global average temperatures have “risen from near the coldest to the warmest levels” in the past 11,300 years, the 2013 study authors explain. Over this same period, emissions of heat-trapping gases from human activities have increased.
• Given the uncertainty inherent in estimating ancient temperatures, the scientists conservatively concluded that the last decade has raised global average temperatures above levels seen for at least 75 percent of the previous 11,300 years. The recent increase in global average temperature is so abrupt that, when scientists plot the data, the end of the line is nearly vertical.
• What about the future? To project future temperatures, the research team used greenhouse gas emission scenarios outlined in the Intergovernmental Panel on Climate Change (IPCC) Climate Change 2007: The Physical Science Basis report, and the authors expect the steep increase to continue through the year 2100, regardless of which one of the emission scenarios from the 2007 report is considered.
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Most of what we consider modern civilization dates to the last 11,000 years—a period of remarkable climatic stability during which people have been able to inhabit the same regions continuously for millennia. The United Nations Educational, Scientific, and Cultural Organization describes Tell Sultan (ancient Jericho) as “the oldest town on earth.” Photo courtesy Seetheholyland.net (some rights reserved).

• For most of the past 10,000 years, the global average temperature has remained relatively stable and low compared to earlier hothouse conditions in our planet’s history. Now, the temperature is among the highest ever recorded not only in the “recent” past—the past 11,000 years, during which modern human civilization developed—but also, probably, over a much longer period.
• Carrie Morrill of the National Climatic Data Center explains, “You’d have to go back to the last interglacial [warm period between ice ages] about 125,000 years ago to find temperatures significantly higher than temperatures of today.”
• Thawing the freezer
• Between, 600 and 800 million years ago—a period geologists call the Proterozoic—evidence suggests the Earth underwent an ice age so cold that ice sheets not only capped the polar latitudes but may have extended all the way to sea level near the equator. Reflecting ever more sunlight into space as they expanded, the ice sheets cooled the climate and reinforced their own growth.
• Global warming events in history shows both natural, ancient warming periods like the Paleocene-Eocene Thermal Maximum (PERM) and recent human-driven warming, marked by accelerating temperature rises since the Industrial Revolution, record-breaking years (like 2024), extreme weather events (heatwaves, floods, droughts), ice melt, sea-level rise, and significant policy milestones such as the IPCC reports and Paris Agreement, all indicating rapid, human-caused climate change.

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1. Ancient & Geological Warming Events

• Paleocene-Eocene Thermal Maximum (PERM: 56 million years ago):
• A sudden, intense warming event (around 6 °C) caused by massive carbon release, offering a glimpse into rapid climate shifts, though slower than today’s.
• Mesozoic & Paleozoic Greenhouse Periods (250-35 million years ago & 500-350 million years ago):
• Times of significantly warmer, “greenhouse” Earth, driven by tectonic activity and greenhouse gases.
• Holocene Climatic Optimum (9,500-5,500 BC):
• A warm period after the last Ice Age, but much cooler than today’s rapid warming.
• Modern & Anthropogenic Warming (Since 1850)
• Industrial Revolutions (1870s onward):
• It marked the beginning of significant human impact on the climate, accelerating CO2 and other greenhouse gas emissions.
• The Keeling Curve (1958):
• Began tracking steadily rising atmospheric CO2 levels, providing key data for global warming theory.
• IPCC & Scientific Consensus (1988-Present):
• The establishment of the Intergovernmental Panel on Climate Change (IPCC) and its reports solidified the link between human activity and warming.
• Accelerated Warming:
• Earth’s temperature has risen about 0.06 °C per decade since 1850, but more than triple that (0.20 °C) per decade since 1982.
• Record-Breaking Years:
• The 10 warmest years on record have all occurred in the last decade (2015-2024), with 2024 being the warmest.
• Significant Modern Climate Impacts & Events
• Extreme Weather: Increased frequency and intensity of heatwaves (Europe 2003, North America 2021), floods (Europe 2021, China 2021), droughts (East Africa 2011, Great Drought 1976), and powerful hurricanes (Ida 2021).
• Ice & Sea Level: Retreating glaciers, declining Arctic sea ice, and record sea-level rise.
• : Montreal Protocol (ozone), Kyoto Protocol, and the Paris Agreement (2015). These events highlight that while Earth’s climate has naturally changed, the current warming trend is unique because of its rapid pace and human cause, demanding s.