Thursday, July 23, 2009

How humans cooled the earth -- 500 years ago

Wednesday, Jan. 7, 2009 16:05 PST

One of the tell-tale signs of a really thought-provoking book is that soon after reading it, you start seeing its thesis replicated everywhere you look. So it has been with one of the tomes I referred to in yesterday's post "Polynesian Chickens in Peru and other Mysteries," Charles Mann's "1491: New Revelations of the Americas Before Columbus."

The massive depopulation of the Americas via smallpox, hepatitis and other diseases introduced by Westerners (perhaps as much as 95 percent of the existing population died in vast pandemics) and the large landscape-altering scale of agriculture practiced across the "New World" by pre-Columbian cultures are two of the big themes of "1491." Both popped up in a presentation made by two scientists at the annual meeting of the American Geophysical Union last December. (Thanks to MongaBay for the tip.)

The scientists contend that after the die-off, massive reforestation on abandoned agricultural land occurred on a large enough scale to contribute significantly to the period of global cooling between 1500 and 1750 known as the "Little Ice Age."

After examining soil samples and sediment cores from numerous locations in Central and South America, Richard Nevle, a visiting scholar at Stanford's Department of Geological and Environmental Sciences at Stanford, and Dennis Bird, also from Stanford, concluded that the reforestation sequestered as much as 10 to 50 percent of the carbon necessary to cool the earth. Up until 1500, the soil samples showed a steady increase in charcoal content, likely generated from human-caused fire used to clear forest. After 1500, the scientists discovered a drastic drop in charcoal content. No more burning.

The scientists acknowledge that reforestation was just one factor in contributing to global cooling. It may not even have been the most critical factor. But the research is sobering nonetheless, in its hint as to humanity's power to alter the fundamental characteristics of life on this planet, long before we were burning fossil fuels as if there were no tomorrow. We did it back then, we're doing it now, and maybe, just maybe, if we exert our collective will in the proper direction, we can fix our mistakes.

Let's just hope it doesn't require another vast die-off to set things to rights.
― Andrew Leonard

February 28, 2006
Did bubonic plague cause the Little Ice Age?

No one's sure what caused the Little Ice Age, when global temperatures dipped by about 1 degree Fahrenheit -- though it was much colder in Europe -- between about 1550 and 1850.

The Thames River regularly froze over and the British held "frost fairs" on the ice. In the winter of 1780, New York Harbor froze, allowing people to walk from Manhattan to Staten Island. And Eskimos landed their kayaks in Scotland as the Arctic ice extended so far.

Many theories have been proposed to explain the chill: a decrease in solar activity, an increase in volcanic activity that would have reduced sunshine heating or a change in ocean circulation that might have cut off warm water from reaching northern Europe.

Now there's a new theory from Dutch researchers:

The team found an increase in cereal pollen from 1200 onwards (reflecting agricultural expansion), followed by a sudden dive around 1347, linked to the agricultural crisis caused by the arrival of the Black Death, most probably a bacterial disease spread by rat fleas.

This bubonic plague is said to have wiped out over a third of Europe's population.

Counting stomata (pores) on ancient oak leaves provided van Hoof's team with a measure of the fluctuations in atmospheric carbon dioxide for the same period. This is because leaves absorb carbon dioxide through their stomata, and their density varies as carbon dioxide goes up and down.

"Between AD 1200 to 1300, we see a decrease in stomata and a sharp rise in atmospheric carbon dioxide, due to deforestation we think," says Dr van Hoof, whose findings are published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.

But after AD 1350, the team found the pattern reversed, suggesting that atmospheric carbon dioxide fell, perhaps due to reforestation following the plague.

What's Happening to the Sun?
Could its unusual behavior herald a new ice age?
By Laurie J. Schmidt Posted 01.27.2009 at 11:26 am

For about 50 years from roughly 1650 to 1700, the Sun took a break from its typical sunspot activity. That phase of solar rest coincided with what we now refer to as "The Little Ice Age" -- a period of cooling on the Earth that resulted in bitterly cold winters, particularly in Europe and North America. Scientists attribute the Little Ice Age to two main causes: increased volcanic activity and reduced solar activity.

According to Woods, even a smaller solar cycle could induce some cooling on Earth. "Not enough to offset the greenhouse gas global warming effect," he said, "but enough to potentially slow it down for a few years." The solar cycle's effect on global temperatures is only about 1/10 of a degree, whereas the greenhouse effect over the past 30 years has been about a full one degree change, Woods said.

Even so, Woods says it's unlikely that we're headed into a "Little Ice Age" scenario. "It's probably unlikely that we will go into a phase where we don't have any sunspot activity for 50 years. We can't eliminate the possibility, but I would say the probability is not high," he said.

"For that to happen, we would have to see no pickup in the Cycle 24 sunspots, but we're seeing a reasonable amount of new activity," said Biesecker. "There is no model we're aware of that can predict that we're going into an ice age -- it's an actual physical limitation of our current understanding."

During the summer of 1816, unexpected climate changes left countries in the Northern Hemisphere suffering from devastating famine and epidemic outbreaks. These weather patterns were the result of the volcanic eruption of Mount Tambora in Sumbawa, Indonesia, on 10th April 1815.

Over the following year, heavy ash-fall filled the air across the globe, preventing sunrays from reaching the earth. The resulting frost and rains devastated crops and caused the “Year without Summer”.

The death toll outside Indonesia ran into hundreds of thousands. With the 117,000 victims who died in the original cataclysm in Indonesia, this was one of the deadliest disasters in history.


If part of the cause of the Little Ice Age was volcanic activity, there would be no reason to expect the same extreme effects now, unless we had similar volcanic activity.

It looks to me like there was a confluence of several things which may have interacted to cause the Little Ice Age.

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