Wednesday, May 30, 2012

An Inconvenient Truth

The article says climate change doomed an ancient civilization:

The mysterious fall of the largest of the world's earliest urban civilizations nearly 4,000 years ago in what is now India, Pakistan, Nepal and Bangladesh now appears to have a key culprit — ancient climate change, researchers say.

I was prepared to read a really strained effort to explain why the Harrappan fall was a warning to us. Perhaps the Harrappan drove sport utility chariots that showed their disdain for the carbon footprint.

But then I read this:

Initially, the monsoon-drenched rivers the researchers identified were prone to devastating floods. Over time, monsoons weakened, enabling agriculture and civilization to flourish along flood-fed riverbanks for nearly 2,000 years.

"The insolation — the solar energy received by the Earth from the sun — varies in cycles, which can impact monsoons," Giosan said. "In the last 10,000 years, the Northern Hemisphere had the highest insolation from 7,000 to 5,000 years ago, and since then insolation there decreased. All climate on Earth is driven by the sun, and so the monsoons were affected by the lower insolation, decreasing in force. This meant less rain got into continental regions affected by monsoons over time."
Eventually, these monsoon-based rivers held too little water and dried, making them unfavorable for civilization.

"The Harappans were an enterprising people taking advantage of a window of opportunity — a kind of "Goldilocks civilization," Giosan said.

Insolation caused the change and not mankind? Who's have ever thought that?

This is why I say I am not convinced that our temperature increases have been tracked for a long enough period to be significant. What are even several decades of increased average temperatures (or decreased averages before then that led to worries of a new ice age) in the face of sun-based trends that last thousands of years?