July 03, 2012
Terraced rice paddies in Yunnan. Many of China's current agricultural areas were made by clearing forests and other natural vegetation hundreds to thousands of years ago. Photo by: Rhett A. Butler.
"The relatively small amounts of carbon dioxide emitted many centuries ago continue to affect atmospheric carbon dioxide concentrations and our climate today, though only to a relatively small extent," says co-author Julia Pongratz with the Max Planck Institute for Meteorology in a press release.
When a forest or other natural vegetation is cleared by burning, carbon dioxide is immediately emitted into the atmosphere. However, decaying vegetation, such as stumps and roots, will seep their carbon into the atmosphere over much long periods of time, sometimes centuries. In addition, carbon has the capacity to stay in the atmosphere for several centuries before being absorbed by the ocean or forests. This means, a portion of carbon from forests that were felled in the 19th Century and before still lingers in our atmosphere today.
Calculating the carbon emitted prior to the Industrial Revolution also provides new insights into climate change today, according to the authors.
Using complex modeling, they found that if one includes land use changes prior to the Industrial Revolution into carbon accounts, it would slightly boost the role of Asia in warming the world. South Asia, which includes India, would then be responsible 7 percent of total global warming, as opposed to 5.1 percent. While China's responsibility would rise from 8.2 percent to 8.7. Populations grew fastest in these region between 800 and 1850 AD, leading to widespread deforestation for agriculture to feed booming populations.
In all, the study's findings would shift the responsibility for current climate change from industrialized nations to developing countries by 2-3 percent. However, the authors emphasize that they are not intending to blame nations for deforestation that occurred hundreds of years by ancestors entirely unaware of the climatic impacts.
"Accounting systems are not natural facts, but human inventions," Ken Caldeira with Carnegie Institution for Science explains. "Once an accounting system is defined, it becomes a matter of scientific investigation to determine what numbers should go in the ledger, but broader questions of who is responsible for what and who owes what to whom are judgments that lie outside the scope of science."
Even with this accounting change, the biggest players in global warming would remain the same: North America, Europe, and the nations of the former Soviet Union are responsible for more than half of the world's current warming. This, despite the fact that India, alone, has a larger population than all of these combined.
According to Pongratz studies such as these provide an inherent warning for society today.
"Looking into the past illustrates that the relatively large amount of carbon dioxide that we are emitting today will continue to have relatively large impacts on the atmosphere and climate for many centuries into the future," she explains.
CITATION: Julia Pongratz and Ken Caldeira. Attribution of atmospheric CO2 and temperature increases to regions: importance of preindustrial land use change. Environmental Research Letters. 2012. 7 034001. doi:10.1088/1748-9326/7/3/034001.
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