During this epoch, often known as the Little Ice Age, temperatures dropped by as much as two degrees Celsius, or 3.6 degrees Fahrenheit. In the roughly five thousand years of recorded human history, there has been one period in which we have had a real taste of our climate’s potential for moodiness, beginning around the start of the fourteenth century and lasting for hundreds of years. The middle is where we happen to be right now-a fact that is responsible for our faulty perception of the earth’s climate as accommodating and stable.
The reality is that our planet oscillates between phases with no ice, phases with all ice, and phases in the middle.
A world without ice is also hard to visualize, though it is by comparison a much more recent phenomenon: perhaps only thirty-four million years ago, crocodiles swam in a freshwater lake we know as the North Pole, and palm trees grew in Antarctica. A world entirely covered in ice, from pole to pole-the so-called snowball earth-is something we find it hard to get our heads around, even though the longest and oldest period of total or near-total glaciation, the Huronian glaciation, lasted for three hundred million years. That is partly because the extent of that variability is so difficult to imagine. It is easy to forget just how variable the climate of the earth has been, across the geologic time scale.
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