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. New research from Carnegie's Julia Pongratz and Ken Caldeira shows that carbon dioxide contributions from the pre-industrial era still 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 caused global warming. But clearing forests and other wild areas for agricultural purposes also contribute to atmospheric carbon dioxide, and that has been happening since before industrialization. When unmanaged land is cleared for farming, part of the carbon is released immediately into the atmosphere as a result of burning. 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. 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.