When evaluating the historic contributions made by different countries to the greenhouse gasses found in Earth’s atmosphere, calculations generally go back no further than the year 1840 which is roughly when the industrial revolution began. But this may not be fair since civilization has been around far longer than that. New research from Carnegie’s Julia Pongratz and Ken Caldeira shows that carbon dioxide contributions from the pre-industrial era have an impact on our climate today. Their work is published in Environmental Research Letters. The burning of fossil fuels that came with industrialization released massive amounts of carbon dioxide emissions into the atmosphere, which has helped cause global warming. But clearing forests and other wild areas for agricultural purposes also contributed to atmospheric carbon dioxide, and that has been happening since before industrialization.
The concentration of carbon dioxide (CO2) in Earth's atmosphere is approaching 397 ppm (parts per million) by volume as of May 2012 and rose by about 2.0 ppm/yr during 2000—2009. This current concentration is substantially higher than the 280 ppm concentration present in preindustrial times, with the increase largely attributed to anthropogenic sources. High CO2 is one of the causes of global warming.
When unmanaged land is cleared for farming, part of the carbon is released immediately into the atmosphere as a result of burning. Clearing of land is a common process used by many older cultues as they developed and expanded.
The rest of the carbon form the old forests, including that from roots and wood products, releases carbon as the wood decays over years and centuries, meaning that carbon from pre-industrial activities is still being emitted into the atmosphere. Furthermore, a part of carbon dioxide emissions remain in the atmosphere for many centuries, because the ocean and vegetation on land absorb carbon dioxide only slowly over time. As a result, there is a warming effect long after the initial clearing of land.
"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," Pongratz, who is now at the Max Planck Institute for Meteorology, said. "But 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."
Moreover, the effect of accounting for pre-industrial emissions can have important consequences for the amount of climate change caused by certain regions. In some regions, such as North America, preindustrial era clearing is only a small part of the total carbon picture because such massive quantities have been released by burning fossil fuels. But in other regions, particularly China and India, the ratio of preindustrial to industrial emissions is much higher.
The world’s population increased about five-fold between 800 and 1850 AD and half that growth occurred in China and India. This led to substantial deforestation in the preindustrial era. On the other side of the coin, cumulative post-industrial fossil fuel carbon emissions for these nations are relatively low, only reaching substantial levels in recent years.
Using advanced mathematical models, Pongratz and Caldeira determined that accounting for pre-industrial emissions shifts attribution of global temperature from industrialized nations to developing nations by up to 2 to 3 %. For example, the study found that considering emissions from pre-industrial land-use change increases the amount of total global warming that can be attributed to emissions from South Asia (a region that includes India) from 5.1% to 7% -- an increase of 37% in the amount previously attributed to this region. Emissions from North America, Europe, and the former Soviet Union have caused more than half of all global warming, even though fewer people live in those regions combined than live in India alone.
The researchers note that their work is not intended to increase the blame on people living in the developing world today for our current climate problems based on what their ancestors did centuries ago, particularly considering the much larger climate impact being made by modern industrialized nations on a daily basis.
Burning fossil fuels such as coal and petroleum is the leading cause of increased anthropogenic CO2; deforestation is the second major cause. In 2010, 9.14 gigatonnes of carbon (33.5 gigatonnes of CO2) were released from fossil fuels and cement production worldwide, compared to 6.15 gigatonnes in 1990. In addition, land use change contributed 0.87 gigatonnes in 2010, compared to 1.45 gigatonnes in 1990. In the period 1751 to 1900 about 12 gigatonnes of carbon were released as carbon dioxide to the atmosphere from burning of fossil fuels, whereas from 1901 to 2008 the figure was about 334 gigatonnes.
For further information see Pre-industrial.
Deforestation image via Wikipedia.