Big History and Climate Change

This is a follow-up to yesterday’s post on big history and Christianity.

From the point of view of “big history” the earth had been through a climate change rollercoaster in its 4.6 billion years of life. We can say that the average temperature rose dramatically between 55 and 50 million years ago, after the dinosaurs vanished. It cooled again 35 million years ago, and warmed again about 12 million years ago, the warmest it had been in 35 million years. Then it cooled again, leading to the development of grasslands, covering one-third of the world’s surface—this turned out to be crucial for the evolution of humanity.

In the last 2 million years, the earth has gotten into a temperature range with hot and cold cycles tipping back and forth. How can this be explained? Well, this seems to result from tiny changes in the tilt of the earth’s axis, in its elliptical oval, and in its wobble on its axis. Each of these three factors have their own patterns that sometimes reinforce, sometimes contradict, each other. Also, the magnetism of the poles reverses about every half million or so years (there have been 282 flips in the past 10 million years). Plus, other factors such as volcanic activity and extra-tertestrial intrusion can affect the climate for long periods of time.

Over the last million years there have been about ten ice ages, at intervals of about 100,000 years. The last one, the Great Ice Age, began 90,000 years ago and reached its peak around 20,000 years ago. It then began to melt, and the last 10,000 years can be regarded as a warming period, with temperatures 1.8 to 5.4 degrees warmer than during the glacial periods. The thaw lasted between 5,000-7,000 years and the ice caps started melting between 14,000-11,000 years ago. The land bridge between Asia and America vanished. The connection between England and Europe was lost. Spain was sundered from Africa , Sri Lanka was separated from India, and the Philippines and Taiwan split from Korea. Large rivers—including the Nile, the Ganges, the Yellow, the Indus, the Tigris, and Euphrates, the rivers that would shape human civilization—were formed. By 10,000 years ago, the sea had risen by 400 feet. Massive flooding continued. In around 5,600BC, the Mediterranean sea rose so high that it created the Bosphorus strait. The memory of the great flood is etched into our collective memory, and appears in the history of revelation.

Looking at “big history” adds a whole new perspective to the current phenomenon of man-made global warming. The detractors would surely look at this history and point to the frequent and unpredictable dramatic climate changes that have marked our planets history. They point to natural factors, such as the earth’s tilt in relation to the sun and volcanic eruptions. They point to the medieval warming period and following little ice age.

But this gets it all wrong, for this kind of argument fails to see the big picture. It starts from a rather myopic pespective. It looks at the passage of time from the human perspective, not from the earth’s history. In our current phase, the kind of temperature increase that we predict today should take place only every 100,000 years or so. We are only 10,000 years into the warmer period, so it is an aberration. The last time we saw that kind of temperature increase, and the associated rise in sea levels, was during the recession of the last ice age around 10,000 BC. And that thaw lasted up to 7,000 years; we expect our global warming to occur in a few hundred. That adds some perspective to those who accuse Al Gore of hiding the fact that the model predictions he highlights are not immediate, and would take a few hundred years to come through. Well, from “big history”, there is no difference at all between next year and two hundred years time. We also need to put the medieval warming period to rest, as that—while it did have pronounced effects—was a mere blip on the radar. Now, we are seeing the effects of climate changes akin to what we saw 8,000 years ago. If you still don’t think that is a problem, consult your bible.