Centennial and Millennial climate-carbon cycle feedback analysis for future anthropogenic climate change

Abstract: Increased anthropogenic emission of CO2 is alleged to impact the climate system in the future, which will affect the feedback between carbon cycle and climate change. In this project, a climate-carbon cycle feedback analysis has been conducted by using long simulated time series (2001 – 3000) data, derived from the Max-Planck-Institute / University of Wisconsin-Madison Earth System Model (MPI/UW ESM). This complex Earth system model was forced by historical emissions of CO2 and by three IPCC SRES scenarios, A2, A1B and B1 till 2100, then for the remainder (2100-3000), an exponential decrease of CO2 emissions was assumed. The analysis has been calculated for the 21st century and for the year 3000, to study the short term (100 year) and long term (1000 year) climate-carbon cycle feedback. In addition, there is not only a difference in time period but also centennial time scale represents a transient state where CO2 forcing continues to increase; on the other hand millennium time scale represents a near equilibrium state of the Earth system against CO2 forcing. For both the centennial and millennial time scale, this complex Earth system model results in positive feedbacks between carbon cycle and climate change for all three scenarios (A2, A1B, and B1). The magnitude of this positive feedback will be stronger by the end of the millennium (3000). This positive feedback clearly indicates that climate change will reduce the carbon uptake by the Earth system due to the climate carbon cycle feedback, thus there will be more remaining CO2 in the atmosphere which is able to produce an additional warming on climate system. The relative magnitude of this positive feedback varies depending on scenarios. For the A2 scenario, this positive feedback has increased by 9% and 39% for 21st century, and for the year 3000, respectively compared to the 20th century. For the A1B scenarios, it has increased by 10% and 30%, respectively, and for the B1 scenario, it has increased by 7% and 14% correspondingly.