1 of 9 Projected state of the Arctic Sea Ice and Permafrost by 2030 By Karsten Steinhaeuser, Esther Parish, Alex Sorokine, Auroop R. Ganguly* Oak Ridge National Laboratory, Oak Ridge, TN 37830 *Corresponding Author: Geographic Information Science and Technology Group Computational Science and Engineering Division Oak Ridge National Laboratory, Oak Ridge, TN, 37830 Email: gangulyar@ornl.gov Phone: 865-241-1305 Programmatic Point of Contact: Blair Ross National Security Directorate Department of Defense Programs Oak Ridge National Laboratory, Oak Ridge, TN 37830 Email: rossb@ornl.gov Phone: 865-576-1034 Background The United States Department of Defense (US DOD) requires an understanding of Arctic sea ice extent and thickness, as well as permafrost in the Northern hemisphere, for an exercise focused on preparedness levels and threat assessments in light of anticipated climate change in the 2030s. The deliverables include visual products, based on supporting data analysis and interpretation, which will allow military planners to utilize one plausible scenario. The analysis and visuals presented in this report are based on outputs from the Community Climate System Model version 3 (CCSM3). The science grounding relies on comparisons of the relevant CCSM3 model outputs with observations in the current decade, as well as through the use of state-of-the-art approaches from the recent literature. While multi-model ensembles are typically used in synthesis and assessment products of this nature (e.g., IPCC 2007), here we rely on the use of one of the IPCC s suite of models, the CCSM3, primarily because of our familiarity with the model. The CCSM3 simulations used here are based on the IPCC Special Report on Emissions Scenario (SRES) A2, which is a relatively aggressive emissions scenario (IPCC 2007), even though recent emissions appear to be trending higher (Raupach et al. 2007).
2 of 9 Arctic Sea Ice The US DOD exercise requires twelve maps, one for each month, of Arctic sea ice extent and thickness in the 2030 s. The projections generated here use simulations from the Community Sea Ice Model component of CCSM3 forced with the A2 scenario. Specifically, the following variables are used here: sea ice concentration (sic) and sea ice thickness (sit). Sea ice extent is defined as the area covered by a concentration of at least 15 percent 1. As a baseline validation, we compare the total area computed from model output to observations 2 (Figure 1). The results show that (i) the periods are aligned, (ii) there is significant agreement on the extent during the summer months, and (iii) the model tends to over-estimate the extent during the winter months. We conclude that the match between sea ice extent from CCSM3 and observations is sufficient to justify the use of CCSM3 model outputs for this exercise. This decision is further supported by a similar comparison performed by Stroeve et al. (2007) involving multiple models, which shows that while most models under-estimate the decline in sea ice CCSM3 model simulations match observations more closely than many other climate models within the IPCC s suite of models (IPCC 2007) used for the Fourth Assessment Report (AR4). Figure 1. Comparison of Arctic sea ice extent from model and observation The projections are based on the monthly decadal-averages centered around 2030 (i.e., 2025-2034). In other words, for each month, sea ice extent and thickness from CCSM3 are averaged over the entire decade, leading to twelve monthly decadal-average maps. The area covered by an average of at least 15 percent of sea ice defines the sea ice boundary 1. In addition to extent of the sea ice, the sea ice thickness produced by the CCSM3 climate model is displayed through a color gradient within the sea ice boundary. Figure 2 presents sample visuals based on these definitions of sea ice extent and thickness for each monthly average in the 2030s. 1 This definition is used by the National Snow and Ice Data Center (http://nsidc.org/data/seaice_index/) as well as in recent publications on sea ice extent (e.g., http://www.nature.com/ngeo/journal/v2/n5/abs/ngeo467.html) 2 Based on satellite imagery, provided by the National Snow and Ice Data Center (http://nsidc.org/data/seaice_index/)
Figure 2. Sample visuals of monthly Arctic sea ice extent and thickness for 2030 (decadal average) 3 of 9
4 of 9 Northern Hemisphere Permafrost The US DOD exercise requires two maps of permafrost in the Northern hemisphere for 2030, one oriented to show North America (specifically, the United States including Alaska, Canada, and Greenland) and the other to show Europe (specifically, Scandinavia and Russia). Projections generated here are based on the Community Land Model component of CCSM3 forced with the A2 scenario. Specifically, we use simulations of soil temperature (TSOI). Permafrost is defined as ground that remains at or below 0 C for at least two consecutive years 3. Lawrence and Slater (2005) adopt this definition and compare permafrost conditions from CCSM3 and observations (see Figure 1 in their paper cited here, specifically panels (a) and (c)). They use all ten soil layers modeled in CCSM3 and find reasonable agreement between model and observations. For our materials, we use the same definition of permafrost, but only consider the deepest layer centered at a depth of 2.86m. In addition, rather than visualizing the depths at which permafrost persists, we show the number of months in the twoyear period 2029-2030 for which this deep layer remains at or below 0 C. A visualization of average monthly permafrost as defined here may be more relevant for military planners in the context of the US DOD exercise. Sample visuals are presented in Figures 3 and 4. Figure 3. Sample visual of permafrost conditions in North America (color scale indicates number of months ground remains at or below 0 C) 3 This definition is provided by the International Permafrost Association (http://ipa.arcticportal.org/index.php/resources/what-is-permafrost.html)
5 of 9 Figure 4. Sample visual of permafrost conditions in Northern Europe (color scale indicates number of months ground remains at or below 0 C) Limitations As a baseline validation, we compare the soil temperature from model output to reanalysis data 4 (serving as the best proxy for global observations). Because we are primarily concerned with conditions in high latitudes, we only consider land areas between 60N and 90N. To match the available reanalysis data, which is an average value for soil 10cm-200cm in depth, we take the average over the corresponding six layers (4 through 9) of the climate model. The results are shown in Figure 5. It is apparent that, while some seasonal variability is captured by the model, there are significant differences in both mean and amplitude of the two series. Thus, permafrost areas shown in these materials are likely to under-estimate the actual extent. Future research on permafrost conditions should therefore consider multi-model outputs and explore alternate data sources. However, the correlation is very high (nearly 0.95), suggesting that bias-correction of model outputs using a statistical (e.g., regressive) model may be possible. Figure 5. Comparison of soil temperature from model and observation 4 Based on the NCEP/NCAR Reanalysis project, provided by NOAA (http://www.esrl.noaa.gov/psd//data/gridded/data.ncep.reanalysis.html)
6 of 9 Appendix A Deliverable Maps The final deliverable consists of 14 maps created using commercial GIS software; an example is shown in Figure 6. In addition to sea ice extent and thickness (depicted by a blue-to-white color gradient) the maps also contain country boundaries (grey), oceans and major rivers (blue), various military installations (red), as well as topography and the prime meridian for orientation. All maps are rendered at sufficient resolution for overhead projection or color printing. Figure 6. Example of a deliverable-quality map
7 of 9 Appendix B Final Deliverables: Arctic Sea Ice Figure 7. Final deliverable maps for Arctic sea ice extent and thickness supplied to the US DOD
8 of 9 Appendix C Final Deliverables: Permafrost Conditions Figure 8. Final deliverable maps for permafrost conditions supplied to the US DOD (at our sponsor s request, the final maps show only areas where the ground remains frozen under the active layer as opposed to the full range of 1-24 months)
9 of 9 References Arzel, O., Fichefet, T., and Hugues Goosse (2006): Sea ice evolution over the 20th and 21st centuries as simulated by current AOGCMs. Ocean Modeling, 12, 401-415. IPCC (2007): The Fourth Assessment Report. Intergovernmental Panel on Climate Change. Available from the Internet: http://www.ipcc.ch/ Lawrence, D.M., and Andrew G. Slater (2005): A projection of severe near-surface permafrost degradation during the 21st century. Geophysical Research Letters, 32, L24401. Raupach, M. R., G. Marland, P. Ciais, C. L. Quere, J. G. Canadell, G. Klepper, and C. B. Field (2007): Global and regional drivers of accelerating CO2 emissions. Proceedings of the National Academy of Sciences of the United States of America, 104 (24): 10288-10293. Stroeve, J., Holland, M.M., Meier, W., Scambos, T., and Mark Serreze (2007): Arctic sea ice decline: Faster than forecast. Geophysical Research Letters, 34, L09501. Acknowledgments The authors thank the following colleagues at the Oak Ridge National Laboratory for their reviews, help and support: Blair Ross for programmatic support, Shih-Chieh Kao for assisting in the problem definition and review of solution strategies, Anthony W. King and David J. Erickson III for technical reviews within ORNL s publications review system, as well as David Bader, Budhendra Bhaduri, James Hack and Gary Jacobs for their support. This research was funded by the United States Department of Defense and by the Laboratory Directed Research & Development Program of the Oak Ridge National Laboratory, which in turn is managed by UT- Battelle, LLC, for the US Department of Energy under Contract DE-AC05-00OR22725. The United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.