Page 54 - Morgan Housel - The Psychology of Money_ Timeless Lessons on Wealth, Greed, and Happiness-Harriman House Limited (2020)

In the early 1900s a Serbian scientist named Milutin Milanković studied the
Earth’s position relative to other planets and came up with the theory of ice
COBACOBA
ages that we now know is accurate: The gravitational pull of the sun and

moon gently affect the Earth’s motion and tilt toward the sun. During parts
of this cycle—which can last tens of thousands of years—each of the
Earth’s hemispheres gets a little more, or a little less, solar radiation than
they’re used to.

And that is where the fun begins.

Milanković’s theory initially assumed that a tilt of the Earth’s hemispheres
caused ravenous winters cold enough to turn the planet into ice. But a
Russian meteorologist named Wladimir Köppen dug deeper into
Milanković’s work and discovered a fascinating nuance.

Moderately cool summers, not cold winters, were the icy culprit.

It begins when a summer never gets warm enough to melt the previous

winter’s snow. The leftover ice base makes it easier for snow to accumulate
the following winter, which increases the odds of snow sticking around in
the following summer, which attracts even more accumulation the
following winter. Perpetual snow reflects more of the sun’s rays, which
exacerbates cooling, which brings more snowfall, and on and on. Within a

few hundred years a seasonal snowpack grows into a continental ice sheet,
and you’re off to the races.

The same thing happens in reverse. An orbital tilt letting more sunlight in
melts more of the winter snowpack, which reflects less light the following
years, which increases temperatures, which prevents more snow the next
year, and so on. That’s the cycle.

The amazing thing here is how big something can grow from a relatively
small change in conditions. You start with a thin layer of snow left over
from a cool summer that no one would think anything of and then, in a

geological blink of an eye, the entire Earth is covered in miles-thick ice. As
glaciologist Gwen Schultz put it: “It is not necessarily the amount of snow
that causes ice sheets but the fact that snow, however little, lasts.”