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.
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Sed contra:
1) Seeing that we’re only 10,000 years into our current warming cycle, it’s not necessarily out of keeping that things should continue to warm for another ten millenia _naturally_. Warming cycles in the past have at times resulted in virtually all the ice caps melting. We’re not there yet. _If_ (and it’s a big if) the ice caps are slated to melt this warming cycle anyway, then frankly even if it’s slated to very hard on the human civilization that has sprung up on the planet in the last 10,000 years, we’re along for the ride and are going to have to learn to live with it.
2) While it’s true that the 200-500 years over which the current warming trend is estimated to melt the Greenland and a fair amount of the Arctic ice, is very short on a geologic scale, it’s not the geologic world that’s in danger: it’s civilization. Now, 200+ years is a very long time for civilization. Think of all the moving and changing that’s gone on in the last 200 years. So if it is the case that we’ve slated ourselves for some big climate and sea level changes in the next 200 years, we shall have every chance to deal with it.
On the side of alarm:
We have six billion souls on this planet. We’ve just simply never done that before. A mere two hundred years ago, we had less than a billion. Given that human civilization is undertaking an unprecidented trip into the unknown: we simply don’t know what would happen.
And hey, nothing is certain. If a decent size comet hits us next year (as has the tendency to happen every few million years) we could go into a global cold snap for a few years — those of us who aren’t washed away by tsunami, that is.
We’re sure getting a big dose of Global Warming here in the midwest this weekend…