Reversing the Trend: Recarbonization of the Earth
Change in management practices required
A new paper by Dr. Richard Houghton, entitled “Historic changes in terrestrial carbon storage,” explores the potential for re-carbonization of the Earth. The paper appears in the book, Recarbonization of the Biosphere: Ecosystems and the Global Carbon Cycle. Taking an interesting perspective and discussing the decades-long de-carbonization of the Earth, he reasons that any recarbonization will have to reverse this trend. Dr. Houghton notes a convenient natural process whereby, beginning in the 1950s, annual net emissions of carbon (C) from historic human land use appear to have been offset by a natural terrestrial C sink—for example an environmentally caused accumulation of carbon in tree growth. Reasons for this natural terrestrial sink include carbon dioxide (CO2) fertilization, nitrogen (N) deposition through manmade fertilizers, changes in climate, and a reduction in natural disturbances. Nature has been helping remove carbon from the atmosphere, reversing direct human activities of land mismanagement.
Human use of land has reduced the amount of C in terrestrial ecosystems, probably since the first use of fire as a tool for clearing land thousands of years ago. Because variations in climate have also affected C storage over this period, it is difficult to attribute long-term changes in terrestrial C to direct human activity. Over the last 150–300 years, however, reconstructions of land use and land-use change suggest that between ∼100 and ∼200 Pg (1 petagram = 1 trillion kg) C were lost from land, largely from the conversion of forests to agricultural lands. This loss of C over the past century or so is greater than the loss attributable to human activity for all of time before 1850. Most of the loss since 1850 has been from the loss of forest biomass, while the loss of C from soil organic matter (SOM) as a result of cultivation is estimated to have contributed ∼25% of the net loss. The restoration of forests on cleared lands could, in theory, re-carbonize the biosphere with 100–200 Pg C; but most of these lands are currently in use and unlikely to be returned to forests. A change in management practices would have to reverse the centuries-long loss of C.
1Houghton, R.A. 2012. Historic changes in terrestrial carbon storage. In Recarbonization of the Biosphere: Ecosystems and the Global Carbon Cycle, ed. R. Lal, K. Lorenz, R.F. Hüttl, B.U. Schneider, and J. von Braun, 59-82. Springer, Dordrecht, the Netherlands.
Ian Vorster, Director of Communications,