Funding is provided to further test the early anthropogenic hypothesis (EAH) that agriculture produced greenhouse-gas emissions large enough to reverse natural downward trends in carbon dioxide and methane concentrations several thousand years ago by driving atmospheric levels of both gases upward and keeping the climate anomalously warm.
Specifically, the researchers plan to: (1) re-examine a model parameterization that artificially limit snow thickness, in order to determine how this constraint affects the extent of permanent snow cover; (2) run model simulations with modern insolation but varying carbon dioxide and methane levels to determine the threshold for present-day glacial inception; (3) assemble data on modern and little ice age mountain glaciers and ice caps for comparison to the model simulations; (4) assemble archeological data on the spread of rice irrigation and livestock tending across southern Asia; and (5) conduct experiments with the NCAR CCSM4 model that include: (a) a 'no anthro' experiment using interactive vegetation with carbon dioxide physiology and a dynamical ocean to assess the full climatic impact of early agricultural greenhouse gases; (b) an experiment simulating late pre-industrial times in order to parcel out the climatic effects of early-agricultural versus industrial-era anthropogenic gases; and (c) an experiment using only direct carbon dioxide and methane inputs from humans to determine whether carbon dioxide feedbacks from the ocean can account for the full carbon budget needed to support a 35-40 parts per million atmospheric carbon dioxide anomaly.
This research is potentially transformative because it provides a new perspective on climate forcing and challenges the broader science community's understanding of the extent of human impacts on climate.
This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
