Environment

Deforestation driving CO2 buildup

Deforestation driving CO2 buil...
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Genghis Khan and his Mongol hordes had an impact on the global carbon cycle as big as today's annual demand for gasoline. The Black Death, on the other hand, came and went too quickly for it to cause much of a blip in the global carbon budget. Dwarfing both of these events, however, has been the historical trend towards increasing deforestation, which over centuries has released vast amounts of carbon dioxide into the atmosphere, as crop and pasture lands expanded to feed growing human populations. Even Genghis Kahn couldn't stop it for long.

"It's a common misconception that the human impact on climate began with the large-scale burning of coal and oil in the industrial era," says Julia Pongratz of the Carnegie Institution's Department of Global Ecology, lead author of a new study on the impact of historical events on global climate published in the January 20, 2011, online issue of The Holocene. "Actually, humans started to influence the environment thousands of years ago by changing the vegetation cover of the Earth's landscapes when we cleared forests for agriculture."

Clearing forests releases carbon dioxide into the atmosphere when the trees and other vegetation are burned or when they decay. The rise in atmospheric carbon dioxide resulting from deforestation is recognizable in ice cores from Greenland and Antarctica before the fossil-fuel era.

But human history has had its ups and downs. During high-mortality events, such as wars and plagues, large areas of croplands and pastures have been abandoned and forests have re-grown, absorbing carbon dioxide from the atmosphere.

Pongratz decided to see how much effect these events could have had on the overall trend of rising carbon dioxide levels. Working with colleagues at the Max Planck Institute for Meteorology in Germany and with global ecologist Ken Caldeira at Carnegie, she compiled a detailed reconstruction of global land cover over the time period from 800 AD to present and used a global climate-carbon cycle model to track the impact of land use changes on global climate. Pongratz was particularly interested in four major events in which large regions were depopulated: the Mongol invasions in Asia (1200-1380), the Black Death in Europe (1347-1400), the conquest of the Americas (1519-1700), and the Fall of the Ming Dynasty in China (1600-1650).

"We found that during the short events such as the Black Death and the Ming Dynasty collapse, the forest re-growth wasn't enough to overcome the emissions from decaying material in the soil," says Pongratz. "But during the longer-lasting ones like the Mongol invasion and the conquest of the Americas there was enough time for the forests to re-grow and absorb significant amounts of carbon."

The global impact of forest re-growth in even the long-lasting events was diminished by the continued clearing of forests elsewhere in the world. But in the case of the Mongol invasions, which had the biggest impact of the four events studied, re-growth on depopulated lands stockpiled nearly 700 million tons of carbon absorbed from the atmosphere. This is equivalent to the world's total annual demand for gasoline today.

Pongratz points out the relevance of the study to current climate issues. "Today about a quarter of the net primary production on the Earth's land surface is used by humans in some way, mostly through agriculture," she says. "So there is a large potential for our land-use choices to alter the global carbon cycle. In the past we have had a substantial impact on global climate and the carbon cycle, but it was all unintentional. Based on the knowledge we have gained from the past, we are now in a position to make land-use decisions that will diminish our impact on climate and the carbon cycle. We cannot ignore the knowledge we have gained."

16 comments
LTWAN
What method does you use to justify this study?
Todd Dunning
Beating 2005\'s dead horses is unworthy of gizmag, a technology blog that is supposed to bring us the future. A headline like \'Deforestation driving CO2 buildup\' assumes a percentage of the readership hasn\'t already figured out the AGW nonsense for themselves. The subject is completely dead in the MSM, so it\'s surprising to see the corpse re-animated here of all places. Deforested areas have grown back completely to their pre-1970\'s levels due to third world farmers returning to the cities. And unless you are in a \'Department of Global Ecology\' paid to keep the inflow of grants coming in, there\'s not too much anymore for a Greenie to do.
Reason
Todd, hard to imagine more ignorance crammed into a couple of paragraphs, but if you think deforestation has slowed, let alone reversed you need to get out more into your own world if not the third world. Just as a small sample of what you will find, here is a simple graphic from Borneo (third world enough for you?); http://maps.grida.no/go/graphic/extent-of-deforestation-in-borneo-1950-2005-and-projection-towards-2020
Ludwig Heinrich
Interesting enough but I would have appreciated either an explication of their methodology or a link to the study.
donwine
The biggest problem facing mankind today is apathy.
Subtle
Mongol expansion \"causing\" GW and even investigating that the Black Death did not \"cause\" global warming. It\'s so funny that I almost spewed my coffee over my keyboard. Many historians consider that extension of the Mongols south into China was partly driven by pronounced climate cooling following the Medieval Warm Period. This hit Europe rather suddenly when an unusually active period of volcanic activity erupted in Iceland beginning in the early 1300s. Such cooling and increase in precipitation forced severe crop failures such that there was a 10 percent die off. Cooling continued and some researchers consider that this weakened the health of the population which made Europe more susceptible to the Plague, when deaths amounted to one/third to one/half of the population.
Todd Dunning
mcsblues, since I am not a Lefty I will not insult you personally; simply educate you on the value of facts instead of emotions: Der Spiegel, \"Tropiocal Comeback\": http://www.spiegel.de/international/world/0,1518,642199,00.html \"...Is the rainforest truly recovering from overexploitation? And could it be that the consequences of deforestation are not as devastating as environmentalists have been preaching for years? \"There are more secondary than primary rainforests in most tropical countries today,\" explains American biologist Joe Wright. \"On the whole, the amount of land covered by vegetation is stable.\" In tropical countries, in particular, rural flight and urbanization have led to more and more farmers abandoning their fields, allowing new vegetation to grow rampant on the fallow ground. \"The numbers speak for themselves,\" says Wright.\"
Facebook User
Those of you who do not believe in global warming are tratorous to themselves, their country and, of course the environment the we need to survive with. Here\'s proof: CO2 is an infrared absorber, proven. No more need be said, really, but here\'s more. The count has risen 40% in exact correlation with our fossil fuels use (About 100 CUBIC MILES FF\'s converted into CO2). Ice caps are coincidentally melting. What more do you want! Oh, \"it\'s not nice to mess with mother nature\" (that\'ll do it!) Solution: Robotically mass produce solar PV. We already have the tech, just not the will to overcome (yell with a bit of sarcasm) OIL DEPLETION... The Chinese are already doing it successfully (and do you think they are doing it just to be green?), We should be doing it for the THOUSANDS OF SQUARE MILES OF INSTALL JOBS TOO! Here\'s the link... http://www.youtube.com/watch?v=i5nJjlbU5lM Get it?
Reason
Todd, did you actually read the article you referred me to? \"\"The conditions in the small country of Panama cannot be generalized. In the Amazon, cattle ranchers and the agricultural industry are destroying the jungle on a large scale. The undergrowth that thrives in cleared areas is a caricature of a forest.\" Even Wright concedes that Brazil is a \"key region\" for the future of the rainforest. Three-quarters of the Amazon jungle lie in Brazilian territory. Nowhere else is the forest being destroyed so recklessly.\" \"\"Within no more than five years, most of the secondary forests will be burned down or cut down again,\" he says. Cattle ranchers use the fallow fields as pasture, while farmers plant soybeans or cereal crops.\" There\'s more - try reading it again. Oh, and its interesting you think I\'m a \"lefty\". What does politics have to do with being able to see the overwhelming evidence of, and sound science behind our influence on climate change? Are you saying because of your political views you just don\'t want it to be true?
Todd Dunning
mcsblues, global warming...er...climate change...er...global climate disruption; which one are we arguing? Let\'s just pick the middle one for now. We deniers are in a comfortable spot, without our reputation on the line or the possibility of being publicly shown to be fools susceptible to the most juvenile hoax of the century so far. It\'s why I can show my real name here, and you don\'t want to. After you graduate and get a few years of life experience you\'ll find that things that sound oh-so right and good not only mean nothing, but usually are the opposite. The apocalypse theme in particular has always worked for those who seeking to influence the naive and impressionable. In today\'s world, this means liberals. That is why not only do I \"think\" you\'re a Lefty, it is proven by what you have written, and your emotional attachment to this \"scientific\" subject. Followed by ad hominems of \"ignorance crammed into a couple of paragraphs\" that show you can\'t really prove your point. Like creationism, AGW was invented to serve an ignorant, easily swayed demographic searching for validation of their views. Your response is directly in line with the rest of your group, blissfully unaware that AGW has already dropped out of MSM news cycle for a year, and has been publicly declared \'under review\' by the IPCC itself.