Climate Change

Skating on the Genesee River (Rochester), 1862

For most of the last half billion years, Earth was a much warmer place than it is now.

During that time, the continents have drifted together then apart again. The changes in the ocean shape and currents have had a

major effect.

About 3 million years ago the closure of the Atlantic ocean began the series of Ice Ages.

With the Atlantic Ocean separated from the Pacific, ocean currents transport warm water into the North Atlantic. Ironically, that leads to

glaciers forming in the high latitudes as more humid air causes increased snowfalls.

The ice covered 1/3 of the northern hemisphere landmass. Areas just south of the ice weren’t very hospitable.

The glaciers expand and contract over several hundred thousand years. The last glacial expansion is called the

“Wisconsin Ice Age.”

Wisconsin

His theory can explain the glacial advances.

Milankovitch used orbital parameters, which are predictable, to calculate the insolation received by the northern high latitudes. When the

insolation in summer is maximized, glaciers melt.

In the last half a million years, the more usual climate has been the cold times when the glaciers advanced. We live in

a short, warm interglacial period.

It is not an accident that human brain size has quadrupled during the Ice Ages.

You can’t live on the glacier (EF) and the land near the ice is tundra (ET)

The shear face of this glacier means you can’t even climb onto it. Life in this climate will be tough. Only the smart ones who have social groups will survive.

How could people kill such a formidable beast?

Preserved Woolly Mammoth in a Beijing museum (obviously life-sized)

But, if our ancestors evolved in central Africa, they wouldn’t have experienced the glaciers or cold weather associated with them

directly. Nevertheless, they would have noticed the effects.

This is where the apes lived, in relative safety in the trees where they ate fruit, among other things.

When the northern hemisphere gets colder, the subtropical Highs dominate the lower latitudes. The forests disappear and are replaced by grasslands. There are lions in the grass!

What could the apes eat? How could they avoid being eaten?

The average temperature can change very abruptly. 12000 years ago, on our way into the current Interglacial age, it dropped back to Ice Age conditions in one human lifetime. 1000 years later, it

bounced back to warm again just as fast. That was the Younger-Dryas.

If it has happened before, it can happen again.

Since the Wisconsin Ice Age ended, the temperatures have actually been warmer than today. That was the “Climatic Optimum.” The

ancient Egyptian civilization flourished at that time.

During the Medieval Warm Period, the Vikings crossed the Atlantic in

boats like this!

They settled in Greenland (and maybe even in North America),

but were destroyed by the Little Ice Age before Columbus ever sailed to the New World.

Greenland houses among the ruins of the Norse villages

Recently, there has been a little discussion about warming:

Since the Little Ice Age ended around 1900, the entire world, not just the

Northern Hemisphere, seems to be getting

warmer quite rapidly.

What might a change on this time scale mean for

the climates of the world?

Has the warming “paused”? The previous graph seems to level off at the end. From a well-known skeptic, the global temperatures from satellite since 1979:

And the global temperature anomalies: