When evaluating the historic contributions made by different countries to the greenhouse gases found in Earth's atmosphere, researchers generally go back no further than the year 1840, because that is when the Industrial Age was large enough to matter. New research from Carnegie's Julia Pongratz and Ken Caldeira says that carbon dioxide contributions from the pre-industrial era are still having an impact on our climate today.
The burning of fossil fuels that came with industrialization released more carbon dioxide emissions into the atmosphere, which has caused global warming, they say. But clearing forests and other wild areas for agricultural purposes also contributed to atmospheric carbon dioxide, and that has been happening since before industrialization.
In other words, mankind has always been a cancer for Gaia, it is just worse now.
When land is cleared for farming, part of the carbon is released immediately into the atmosphere. The rest of the carbon, 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. They further contend that 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."
Accounting for pre-industrial emissions can have important consequences for the amount of climate change attributed to certain regions. In regions like North America preindustrial clearing is only a small part of the total carbon picture but in other regions, particularly China and India, the ratio of preindustrial emissions was high.
So maybe those two countries should not be exempt from climate treaties because they are still 'developing' - they polluted for a lot longer than America. 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 their own numerical models, Pongratz and Caldeira claim 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 from 5.1% to 7% -- an increase of 37% in the amount previously attributed to this region.
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.
"Accounting systems are not natural facts, but human inventions," Caldeira said. "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."
Published in Environmental Research Letters.