Feeds:
Posts
Comments

Posts Tagged ‘deforestation’

Topic: Myan Crops

For six centuries, the ancient Maya flourished, with more than a hundred city-states scattered across what is now southern Mexico and northern Central America.

 

Then, in A.D. 695, the collapse of several cities in present day Guatemala marked the start of the Classic Maya’s slow decline. Prolonged drought is thought to have played a role, but a study published this week in the journal Geophysical Research Letters adds a new twist: The Maya may have made the droughts worse by clearing away forests for cities and crops, making a naturally drying climate drier.

“We’re not saying deforestation explains the entire drought, but it does explain a substantial portion of the overall drying that is thought to have occurred,” said the study’s lead author Benjamin Cook, a climate modeler at Columbia University’s Lamont-Doherty Earth Observatory and the NASA Goddard Institute for Space Studies.

More than 19 million people were scattered across the Maya empire at its height, between A.D. 250 and A.D. 900. Using population records and other data, the study authors reconstructed the progressive loss of rainforest across their territory as the civilization grew. The researchers ran computer simulations to see how lands newly dominated by crops would have affected climate. In the heavily logged Yucatan peninsula, they found that rainfall would have declined by as much as 15 percent while in other Maya lands, such as southern Mexico, it would have fallen by 5 percent. Overall, the researchers attributed 60 percent of the drying estimated at the time of the Maya’s peak to deforestation.

As crops like corn replace a forest’s dark canopy, more sunlight bounces back into space, said Cook. With the ground absorbing less energy from the sun, less water evaporates from the surface, releasing less moisture into the air to form rain-making clouds. “You basically slow things down—the ability to form clouds and precipitation,” he said.

 

 

 

The idea that the Maya changed the climate by clearing away jungle, partly causing their demise, was popularized by historian Jared Diamond in his 2005 book Collapse. In the first study to test the hypothesis, climate modeler Robert Oglesby and his colleagues ran a computer simulation of what total deforestation of Maya lands would do to climate. Their results, published in 2010in the Journal of Geophysical Research, showed that wet season rainfall could fall 15 to 30 percent if all Maya lands were completely cleared of trees. Oglesby, who was not involved in the Cook study, said that Cook’s estimate of a 5 to 15 percent reduction in rainfall, though lower than his own, makes sense since Cook’s simulation used a realistic tree-clearing scenario.

Archeologists attribute a variety of factors to the collapse of the Classic Maya, whose ancestors are still living today in parts of Mexico, Guatemala, Belize, El Salvador and Honduras. In addition to a drying climate in several regions, the city-states struggled with overpopulation, changing trade routes, war and peasant revolts.

The Maya cleared the forests to grow corn and other crops, but they also needed the trees for cooking large amounts of lime plaster used in constructing their elaborate cities. Thomas Sever, an archeologist at the University of Alabama, Huntsville, and a co-author of the 2010 deforestation study, said that it would have taken 20 trees to produce a single square meter of cityscape. “When you look at these cities and see all the lime and lime plaster, you understand why they needed to cut down the trees to keep their society going,” he said.

The Maya also lacked the technology to tap the groundwater several hundred feet beneath them. Their reservoirs and canals were able to store and distribute water when rain plentiful, but when the rain failed, they had nowhere to turn. “By the time of the collapse, every square mile of soil had been turned over,” said Sever.

Scientists know from studying climate records held in cave formations and lake sediments that the Maya suffered through a series of droughts yet they continue to debate their severity. In a paper earlier this year in Science, researchers Martín Medina-Elizalde and Eelco Rohling of Mexico’s Yucatan Center for Scientific Research found that annual rainfall may have fallen as little as 25 percent during the Maya’s decline, from about A.D. 800 to A.D. 950. Most of the reduction in rainfall, however, may have occurred during the summer growing season when rain would have been most needed for cultivation and replenishing freshwater storage systems, they added.

Today, many of the Maya’s abandoned cities are overgrown with jungle, especially on the Yucatan peninsula. Satellite images, however, show that deforestation is happening rapidly elsewhere, including in other regions the Maya once occupied. The study may offer a warning about the consequences: “There’s a tremendous amount of change going on in Guatemala,” said Oglesby. “They may be that much more vulnerable to a severe drought.”

Other authors of the study are: Kevin Anchukaitis, Lamont-Doherty; Jed Kaplan, Ecole Polytechnique Federale de Lausanne in Switzerland; Michael Puma, NASA GISS; Max Kelley, NASA GISS and Denis Gueyffier, ONERA, the French Aerospace Lab.

Original Article:

heritagedaily.com

August 21, 2012

Read Full Post »

Topic: The need to go green is ageless

For 1200 years, the Maya dominated Central America. At their peak around 900 A.D., Maya cities teemed with more than 2,000 people per square mile — comparable to modern Los Angeles County. Even in rural areas the Maya numbered 200 to 400 people per square mile. But suddenly, all was quiet. And the profound silence testified to one of the greatest demographic disasters in human prehistory — the demise of the once vibrant Maya society.

What happened? Some NASA-funded researchers think they have a pretty good idea.

“They did it to themselves,” says veteran archeologist Tom Sever.

“The Maya are often depicted as people who lived in complete harmony with their environment,’ says PhD student Robert Griffin. “But like many other cultures before and after them, they ended up deforesting and destroying their landscape in efforts to eke out a living in hard times.”

A major drought occurred about the time the Maya began to disappear. And at the time of their collapse, the Maya had cut down most of the trees across large swaths of the land to clear fields for growing corn to feed their burgeoning population. They also cut trees for firewood and for making building materials.

“They had to burn 20 trees to heat the limestone for making just 1 square meter of the lime plaster they used to build their tremendous temples, reservoirs, and monuments,” explains Sever.

He and his team used computer simulations to reconstruct how the deforestation could have played a role in worsening the drought. They isolated the effects of deforestation using a pair of proven computer climate models: the PSU/NCAR mesoscale atmospheric circulation model, known as MM5 (http://www.mmm.ucar.edu/mm5/), and the Community Climate System Model, or CCSM (http://www.ccsm.ucar.edu/).

“We modeled the worst and best case scenarios: 100 percent deforestation in the Maya area and no deforestation,” says Sever. “The results were eye opening. Loss of all the trees caused a 3-5 degree rise in temperature and a 20-30 percent decrease in rainfall.”

//

The results are telling, but more research is needed to completely explain the mechanisms of Mayan decline. Archeological records reveal that while some Maya city-states did fall during drought periods, some survived and even thrived.

“We believe that drought was realized differently in different areas,” explains Griffin. “We propose that increases in temperature and decreases in rainfall brought on by localized deforestation caused serious enough problems to push some but not all city-states over the edge.”

The Maya deforested through the use of slash-and-burn agriculture – a method still used in their old stomping grounds today, so the researchers understand how it works.

“We know that for every 1 to 3 years you farm a piece of land, you need to let it lay fallow for 15 years to recover. In that time, trees and vegetation can grow back there while you slash and burn another area to plant in.”

But what if you don’t let the land lay fallow long enough to replenish itself? And what if you clear more and more fields to meet growing demands for food?

“We believe that’s what happened,” says Griffin. “The Maya stripped large areas of their landscape bare by over-farming.”

Not only did drought make it difficult to grow enough food, it also would have been harder for the Maya to store enough water to survive the dry season.

“The cities tried to keep an 18-month supply of water in their reservoirs,” says Sever. “For example, in Tikal there was a system of reservoirs that held millions of gallons of water. Without sufficient rain, the reservoirs ran dry.” Thirst and famine don’t do much for keeping a populace happy. The rest, as the saying goes, is history.

“In some of the Maya city-states, mass graves have been found containing groups of skeletons with jade inlays in their teeth – something they reserved for Maya elites – perhaps in this case murdered aristocracy,” he speculates.

No single factor brings a civilization to its knees, but the deforestation that helped bring on drought could easily have exacerbated other problems such as civil unrest, war, starvation and disease.

Many of these insights are a result of space-based imaging, notes Sever. “By interpreting infrared satellite data, we’ve located hundreds of old and abandoned cities not previously known to exist. The Maya used lime plaster as foundations to build their great cities filled with ornate temples, observatories, and pyramids. Over hundreds of years, the lime seeped into the soil. As a result, the vegetation around the ruins looks distinctive in infrared to this day.”

“Space technology is revolutionizing archeology,” he concludes. “We’re using it to learn about the plight of ancients in order to avoid a similar fate today.”

Contributors to this research: Archeologist Dr. Tom Sever of UAHuntsville in Huntsville, Alabama; archeologist Dr. William Saturno of Boston University, who is a NASA Intergovernmental Personnel Act Assignee; Rob Griffin, a PhD student at Pennsylvania State University in College Park, Pa, and current Visiting Professional at the National Space Science and Technology Center in Huntsville; Dr. Udaysankar Nair, a research scientist in UAHuntsville’s Earth System Science Center; Daniel Irwin, SERVIR Project Director at NASA’s Marshall Space Flight Center; and paleoclimatologist Dr. Bob Oglesby of the University of Nebraska.

Original article:

redorbit.com

Dauna Coulter, Science @ NASA

October, 2009

Read Full Post »

%d bloggers like this: