In 1815, Mount Tambora on the Indonesian island of Sumbawa erupted with extraordinary force. The eruption and its aftermath killed tens of thousands of people. It is widely described as the largest eruption in recorded history; that is different from the largest in the past 10,000 years.
News traveled slowly at the time. Volcanic material entered the atmosphere. Sulfur gases that formed stratospheric aerosols were particularly important for the longer-lasting reduction in incoming sunlight and the resulting cooling. Sunsets became unusually vivid yet hazy.
The following year, 1816, became known as “The Year Without a Summer.” Crops failed across Europe and North America. Ireland suffered famine followed by a typhus epidemic that claimed tens of thousands of lives. Night frosts lasted into June. Globally, temperatures fell by roughly half a degree Celsius — a seemingly small shift with devastating consequences.
The Little Ice Age
The 19th century was already part of a cooler climatic period often referred to as the Little Ice Age. The timing and severity varied by region; the Little Ice Age was not one uniform, uninterrupted cold spell everywhere. The River Thames froze, and Dutch canals became skating rinks.
Geologists of the time struggled to explain strange features in the European landscape — massive boulders resting far from their origins, Arctic animal remains found in France, and unexplained grooves in rock surfaces.
Early explanations ranged from catastrophic floods to unusual geological pressure events. None proved satisfactory.
The Discovery of Ice Ages
A breakthrough came when Swiss geologist Jean de Charpentier listened to a local lumberjack explain that massive stones had been transported by glaciers. The idea that ice sheets once extended far beyond their present limits gradually gained acceptance.
In 1837, botanist Karl Schimper introduced the term “Ice Age,” proposing that vast ice sheets once covered large portions of Europe, Asia, and North America — a radical claim at the time.
James Croll and Orbital Theory
In the 1860s, James Croll, a self-educated Scottish scientist working as a janitor at Anderson’s University in Glasgow, published groundbreaking research. He proposed that variations in Earth’s orbit could trigger ice ages.
Though initially overlooked due to his position, his calculations suggested that cyclical changes in Earth’s orbital shape influenced climate patterns over tens of thousands of years.
Croll eventually gained recognition and became a member of the Royal Society.
Milankovitch Cycles
Serbian mathematician Milutin Milankovitch later expanded on Croll’s theory. He demonstrated that three key orbital variations affect Earth’s climate:
- Eccentricity (shape of Earth’s orbit)
- Obliquity (axial tilt)
- Precession (axial wobble)
These cycles operate over roughly 20,000, 40,000, and 100,000-year intervals.
Modern climate science confirms that these orbital patterns correlate strongly with glacial and interglacial periods.
Meteorologist Wladimir Köppen further argued that ice ages are driven more by cool summers than harsh winters. If summer temperatures fail to melt accumulated snow, ice sheets expand due to increased solar reflection.
Where We Stand Today
Technically, we still live within an ice age — specifically in a warmer interglacial phase known as the Holocene.
At the peak of the last glacial maximum around 20,000 years ago, ice sheets covered a much larger share of the land than today. Modern estimates put roughly 69% of Earth’s freshwater in glaciers and ice caps.
Ice core samples from Greenland provide detailed climate records spanning roughly 100,000 years. These records show that Earth’s climate has shifted abruptly between warm and cold phases — sometimes rapidly.
Climate Complexity
Climate is shaped by numerous interacting factors:
- Carbon dioxide concentrations
- Continental drift
- Solar activity
- Ocean circulation
- Orbital mechanics
Understanding past climate shifts remains challenging, and predicting future ones is equally complex.
The lesson of climate history is not simplicity — but variability.
Sources for factual corrections
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