CBL4
17th October 2005, 03:28 PM
I recently saw William Ruddiman lecture and I am reading his book Plows, Plagues and Petroleum.
http://www.amazon.com/exec/obidos/tg/detail/-/0691121648/qid=1129583493/sr=8-1/ref=pd_bbs_1/102-7993194-6941760?v=glance&s=books&n=507846
He has developed the hypothesis that farming has effected climate for the last 8000 years. He is a good lecturer and author.
From the Economist in 2003 (before the book was published):
[A]n equally intriguing idea put forward at the [American Geophysical Union] meeting is that the spread of agriculture caused climate change.
In this case, the presumed culprit is forest clearance. Most of the land cultivated by early farmers in the Middle East, Europe and southern China would have been forested. When the trees that grew there were cleared, the carbon they contained ended up in the atmosphere as carbon dioxide, a greenhouse gas. Moreover, one form of farming—the cultivation of rice in waterlogged fields—generates methane, another greenhouse gas, in large quantities. William Ruddiman, of the University of Virginia, explained to delegates his theory that, in combination, these two phenomena had warmed the atmosphere prior to the start of the industrial era by as much as all the greenhouse gases emitted since.
Dr Ruddiman's hypothesis is grounded on recent deviations from the regular climatic pattern of the past 400,000 years. This pattern is controlled by what are known as the Milankovitch cycles, which are in turn caused by periodic changes in the Earth's orbit and angle of tilt toward the sun. One effect of the Milankovitch cycles is to cause regular and predictable changes in the atmospheric concentrations of carbon dioxide and methane. These changes can be followed by studying ice cores taken in Antarctica.
According to Dr Ruddiman, the changes seen in the cores are as regular as clockwork until about 8,000 years ago. At that time carbon dioxide levels begin to rise at a point when they ought to start falling. About 5,000 years ago there is another upward deviation, this time in methane levels. The former, he contends, coincides with the beginning of extensive deforestation associated with the spread of agriculture into Europe and China. The latter coincides with the invention of “wet rice” farming. In combination, he calculates, these upward deviations make the atmosphere about 0.8°C warmer than it would otherwise be at this point in the Milankovitch cycles, independently of any greenhouse warming caused by industrialisation. That has been enough to keep parts of Canada that would otherwise be covered in glaciers, ice-free.
Of course, this is a difficult hypothesis to test. But Dr Ruddiman does have a test of sorts. Three times in the past 2,000 years, there have been periods of cooling (most recently, the “little ice age” of the 17th and 18th centuries). These, he notes, followed the three largest known periods of plague, when the human population shrank in various parts of the world. The first period was a series of plagues that racked the Roman empire from the third to the sixth centuries. The second was the Black Death and its aftermath. The third was the epidemic of smallpox and other diseases that reduced the population of the Americas from some 50m to about 5m in the centuries after Europeans arrived, and which coincided with the little ice age. In each case, a lot of previously farmed land turned back into forest, sucking carbon dioxide out of the atmosphere and cooling the climate. As environmentalists are wont to observe, mankind is part of nature. These observations show just how intimate the relationship is. http://www.economist.com/displaystory.cfm?story_id=2299998
When I asked him how his hypothesis had been received, he said the only serious rebuttal was that deforestation would not produce enough CO2. He said that other scientists believe coal burning (especially in China) would provide the rest.
I do not claim that his hypothesis is true but it is intriguing. He is a reputable scientist who has been studying climate change for decades. He has been published in magazines such as Scientific American, Nature, and Science. He previous research includes how monsoons affect methane in the atmosphere.
ETA: He has been on a book tour and spoke in front of the Skeptic Society. He will be in NY next week.
http://www.nyas.org/events/eventDetail.asp?eventID=4671&date=10/25/2005%206:30:00%20PM
CBL
http://www.amazon.com/exec/obidos/tg/detail/-/0691121648/qid=1129583493/sr=8-1/ref=pd_bbs_1/102-7993194-6941760?v=glance&s=books&n=507846
He has developed the hypothesis that farming has effected climate for the last 8000 years. He is a good lecturer and author.
From the Economist in 2003 (before the book was published):
[A]n equally intriguing idea put forward at the [American Geophysical Union] meeting is that the spread of agriculture caused climate change.
In this case, the presumed culprit is forest clearance. Most of the land cultivated by early farmers in the Middle East, Europe and southern China would have been forested. When the trees that grew there were cleared, the carbon they contained ended up in the atmosphere as carbon dioxide, a greenhouse gas. Moreover, one form of farming—the cultivation of rice in waterlogged fields—generates methane, another greenhouse gas, in large quantities. William Ruddiman, of the University of Virginia, explained to delegates his theory that, in combination, these two phenomena had warmed the atmosphere prior to the start of the industrial era by as much as all the greenhouse gases emitted since.
Dr Ruddiman's hypothesis is grounded on recent deviations from the regular climatic pattern of the past 400,000 years. This pattern is controlled by what are known as the Milankovitch cycles, which are in turn caused by periodic changes in the Earth's orbit and angle of tilt toward the sun. One effect of the Milankovitch cycles is to cause regular and predictable changes in the atmospheric concentrations of carbon dioxide and methane. These changes can be followed by studying ice cores taken in Antarctica.
According to Dr Ruddiman, the changes seen in the cores are as regular as clockwork until about 8,000 years ago. At that time carbon dioxide levels begin to rise at a point when they ought to start falling. About 5,000 years ago there is another upward deviation, this time in methane levels. The former, he contends, coincides with the beginning of extensive deforestation associated with the spread of agriculture into Europe and China. The latter coincides with the invention of “wet rice” farming. In combination, he calculates, these upward deviations make the atmosphere about 0.8°C warmer than it would otherwise be at this point in the Milankovitch cycles, independently of any greenhouse warming caused by industrialisation. That has been enough to keep parts of Canada that would otherwise be covered in glaciers, ice-free.
Of course, this is a difficult hypothesis to test. But Dr Ruddiman does have a test of sorts. Three times in the past 2,000 years, there have been periods of cooling (most recently, the “little ice age” of the 17th and 18th centuries). These, he notes, followed the three largest known periods of plague, when the human population shrank in various parts of the world. The first period was a series of plagues that racked the Roman empire from the third to the sixth centuries. The second was the Black Death and its aftermath. The third was the epidemic of smallpox and other diseases that reduced the population of the Americas from some 50m to about 5m in the centuries after Europeans arrived, and which coincided with the little ice age. In each case, a lot of previously farmed land turned back into forest, sucking carbon dioxide out of the atmosphere and cooling the climate. As environmentalists are wont to observe, mankind is part of nature. These observations show just how intimate the relationship is. http://www.economist.com/displaystory.cfm?story_id=2299998
When I asked him how his hypothesis had been received, he said the only serious rebuttal was that deforestation would not produce enough CO2. He said that other scientists believe coal burning (especially in China) would provide the rest.
I do not claim that his hypothesis is true but it is intriguing. He is a reputable scientist who has been studying climate change for decades. He has been published in magazines such as Scientific American, Nature, and Science. He previous research includes how monsoons affect methane in the atmosphere.
ETA: He has been on a book tour and spoke in front of the Skeptic Society. He will be in NY next week.
http://www.nyas.org/events/eventDetail.asp?eventID=4671&date=10/25/2005%206:30:00%20PM
CBL