Johannes Lehmann et at., Australian climate–carbon cycle feedback reduced by soil black carbon

Letter abstract

---

Nature Geoscience 1, 832-835 (2008)
Published online: 16 November 2008 | doi:10.1038/ngeo358

Australian climate–carbon cycle feedback reduced by soil black carbon

Johannes Lehmann¹, Jan Skjemstad², Saran Sohi³, John Carter⁴, Michele Barson⁵, Pete Falloon⁶, Kevin Coleman³, Peter Woodbury¹ and Evelyn Krull²

Annual emissions of carbon dioxide from soil organic carbon are an order of magnitude greater than all anthropogenic carbon dioxide emissions taken together¹. Global warming is likely to increase the decomposition of soil organic carbon, and thus the release of carbon dioxide from soils^{2, 3, 4, 5}, creating a positive feedback^{6, 7, 8, 9}. Current models of global climate change that recognize this soil carbon feedback are inaccurate if a larger fraction of soil organic carbon than postulated has a very slow decomposition rate. Here we show that by including realistic stocks of black carbon in prediction models, carbon dioxide emissions are reduced by 18.3 and 24.4% in two Australian savannah regions in response to a warming of 3 ^°C over 100 years¹. This reduction in temperature sensitivity, and thus the magnitude of the positive feedback, results from the long mean residence time of black carbon, which we estimate to be approximately 1,300 and 2,600 years, respectively. The inclusion of black carbon in climate models is likely to require spatially explicit information about its distribution, given that the black carbon content of soils ranged from 0 to 82% of soil organic carbon in a continental-scale analysis of Australia. We conclude that accurate information about the distribution of black carbon in soils is important for projections of future climate change.

1. Department of Crop and Soil Sciences, College of Agriculture and Life Sciences, Cornell University, Ithaca, NY 14853, USA
2. CSIRO Land and Water, Glen Osmond, SA 5064, Australia
3. Rothamsted Research, Harpenden, AL5 2JQ, UK
4. Queensland Climate Change Centre of Excellence, Environmental Protection Agency, Indooroopilly, Qld 4068, Australia
5. Bureau of Rural Sciences, Department of Agriculture, Fisheries and Forestry, Canberra, ACT 2602, Australia
6. Met Office Hadley Centre, Fitzroy Road, Exeter EX1 3PB, UK

Correspondence to: Johannes Lehmann¹ e-mail: CL273@cornell.edu

Link to abstract: http://www.nature.com/ngeo/journal/v1/n12/abs/ngeo358.html