Background

1. GC41C-0929 The possibility of persistent cold extremes under 21st century warming scenarios Evan Kodra, Karsten Steinhaeuser, Auroop R. Ganguly GIST Group, CSE Division, Oak Ridge National Laboratory Intensity Duration Most Likely, Lower, and Upper Bound of Events Background • Cold extreme intensity (CEI) is defined as an analogue of heat wave intensity (8-9).The CEI is calculated as the coldest 3-day average of daily maximum temperature in a given year. • Cold extreme duration (CED) is defined as the annual maximum of consecutive frost days, defined in turn as days where minimum temperature is less than or equal to 0 °C. This index has been used in studies related to human mortality (5). • The possibility of decadal or multi-decadal periods of global-average cold spells within an overall anthropogenic warming trend has been previously investigated (1-2). • Here we examine cold extremes, or the statistical attributes of cold events that are of relatively shorter duration, specifically, events lasting from a day to several weeks. • Although it may be more theoretically satisfying to study definitions of cold events based on extreme value theory like ‘100 year temperature events’, they may not mean much in the context of impacts. • Accordingly, we study intensity, duration and frequency (IDF) properties of cold extremes instead, as studied by previous impacts-based research (3-7). Impacts include human mortality, agriculture, recreation, gardening, and plant reproduction and distribution. Figure 3 Figures5 : For each extreme index, the minimum, median, and maximum of the five numbers at each grid are presented, providing a measure of a minimum bound, central tendency and maximum bound respectively, for each grid. Frequency is not shown. Data Five model simulations: INGV-ECHAM4, CSIRO-MK3-5, CNRM-CM3, MRI-CGCM2-3-2A, and CCCMA CGCM3-1 T63 were obtained from CMIP3 maintained by PCMDI.The model runs selected were forced with IPCC SRES A1B, a mid-range future GHG emissions scenario. One initial condition ensemble was selected per model. NCEP/NCAR-1 reanalysis datasets were obtained from NOAA ESRL. A Different Approach Figure 2 Calculation of Indices • In Figure 2-4, counts indicate the number of years out of 2091-2100 where the chosen cold extreme measure surpasses the average cold extreme calculated from 1991-2000. These counts are performed at each grid cell. • In all three figures, bias scores were computed using model and reanalysis data from 1991-2000 to assess credibility of projections. Positive bias scores indicate a cold bias, and negative numbers indicate a warm bias. Frequency Figure 1: Mean decadal change in surface temperature from 1991-2000 to 2091-2100 show projections of global warming. Despite these results, we find surprising lingering of cold extremes at the end of the 21st century. Cold extreme frequency (CEF) is defined as the total number of frost days in a given year, as studied in previous impact-relevant studies (3-4). Figure 6: A simple mean decadal change in CEI does not reveal the same insights on intensity persistence. For example, INGV-ECHAM4 shows quite a few events in the Western US in Figure 1. Here, though, a mean change calculation hides inter-annual variability and hence the persistence of CEI in 2091-2100 is hidden as well. References (1) Easterling D, Wehner M (2009) Is the climate warming or cooling? Geophys Res Lett 36, L08706, DOI:10.1029/2009GL037810. (2) Keenlyside NS, Latif M, Jungclaus J, Kornblueh L, Roeckner E (2008) Advancing decadal-scale climate prediction in the North Atlantic sector. Nature 453, 84-88, doi:10.1038/nature06921. (3) Frich P, Alexander LV, Della-Marta P, Gleason B, Haylock M, Tank AMGK, Peterson T (2002) Observed coherent changes in climatic extremes during the second half of the twentieth Century. Clim. Res. 19: 193–212. (4) Inouye D (2000) The ecological and evolutionary significance of frost in the context of climate change. Ecology Letters 3 (5), 457-463. (5) Ekamper P , van Poppel F, van Duin C, Garssen J (2009) 150 Years of temperature-related excess mortality in the Netherlands. Demographic Research 21 (14): 385-426, DOI: 10.4054/DemRes.2009.21.14. (6) McMichael AJ, Campbell-Lendrum DH, Corvalán CF, Ebi KL, Githeko AK, Scheraga JD, Woodard A (2003) Climate change and human health: risks and responses. World Health Organization, Geneva. (7) Huynen MM, Martens P, Schram D, Weijenberg MP, Kunst AE (2001) The impact of heat waves and cold spells on mortality rates in the Dutch population. Environ Health Perspect. 109(5), 463-470. (8) Meehl GA, Tebaldi C (2004) More intense, more frequent, and longer lasting heat waves in the 21st century. Science 305: 994–997. (9) Ganguly AR, Steinhaeuser K, Erickson III DJ, Branstetter M, Parish ES, Singh N, Drake JB, Buja L (2009) Higher trends but larger uncertainty and geographic variability in 21st century temperature and heat waves. PNAS 106 (37): 15555 – 15559. Discussion and Conclusion • Using a slightly different way of examining cold extremes, we find evidence from five climate models that intensity and duration of cold extremes may persist at end-of-20th-century levels late into the 21st century in many regions, despite unanimous projections of relatively significant warming trends. However, there is no evidence suggesting that frequency will persist in the future. • Considerable inter-model variability exists in projections. Methods of combining projections to reduce uncertainty should be investigated. • The implications for decision-makers are that, even as regional preparedness efforts are made for warming conditions, our ability to respond to cold extremes cannot be compromised. ¶ Point of Contact This research was primarily funded by the Laboratory Directed Research and Development (LDRD) Program of the Oak Ridge National Laboratory (ORNL), managed by UT-Battelle, LLC, for the U.S. Department of Energy under Contract DE-AC05-00OR22725. Other funding sources include DOE, DOD, and HERE. Geog. Information Sci. & Tech. Group Computational Sci. & Eng. Division Oak Ridge National Laboratory Oak Ridge, TN 37831-6017Tel.: +1 (865) 241-1305 Fax: +1 (865) 241- 6261 Auroop R. Ganguly, Ph.D. Email: gangulyar@ornl.gov http://www.ornl.gov/knowledgediscovery/ClimateExtremes Figure 4