2230 JOURNAL OF CLIMATE VOLUME 27 North American Climate in CMIP5 Experiments: Part III: Assessment of Twenty-First-Century Projections* a b c c d ERIC D. MALONEY, SUZANA J. CAMARGO, EDMUND CHANG, BRIAN COLLE, RONG FU, e f g h i KERRIE L. GEIL, QI HU, XIANAN JIANG, NATHANIEL JOHNSON, KRISTOPHER B. KARNAUSKAS, j,k l k m JAMES KINTER, BENJAMIN KIRTMAN, SANJIV KUMAR, BAIRD LANGENBRUNNER, n o,p q m KELLY LOMBARDO, LINDSEY N. LONG, ANNARITA MARIOTTI, JOYCE E. MEYERSON, p m r b e KINGTSE C. MO, J. DAVID NEELIN, ZAITAO PAN, RICHARD SEAGER, YOLANDE SERRA, s t u s h ANJI SETH, JUSTIN SHEFFIELD, JULIENNE STROEVE, JEANNE THIBEAULT, SHANG-PING XIE, v w w CHUNZAI WANG, BRUCE WYMAN, AND MING ZHAO a Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado b Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York c School of Marine and Atmospheric Sciences, Stony Brook University, State University of New York, Stony Brook, New York d Department of Geological Sciences, The University of Texas at Austin, Austin, Texas e Department of Atmospheric Sciences, The University of Arizona, Tucson, Arizona f Department of Earth and Atmospheric Sciences, University of Nebraska–Lincoln, Lincoln, Nebraska g Joint Institute for Regional Earth System Science and Engineering, University of California, Los Angeles, Los Angeles, California h International Pacific Research Center, University of Hawai‘i at Manoa, Honolulu, Hawaii i Woods Hole Oceanographic Institution, Woods Hole, Massachusetts j Atmospheric, Oceanic and Earth Sciences Department, George Mason University, Fairfax, Virginia k Center for Ocean–Land–Atmosphere Studies, Fairfax, Virginia l Division of Meteorology and Physical Oceanography, University of Miami, Miami, Florida m Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, Los Angeles, California n Department of Marine Sciences, University of Connecticut, Avery Point, Connecticut o Wyle Science, Technology and Engineering, College Park, Maryland p Climate Prediction Center, NOAA/NWS/NCEP, College Park, Maryland q NOAA/Climate Program Office, Silver Spring, Maryland r Department of Earth and Atmospheric Sciences, St. Louis University, St. Louis, Missouri s Department of Geography, University of Connecticut, Storrs, Connecticut t Department of Civil and Environmental Engineering, Princeton University, Princeton, New Jersey u National Snow and Ice Data Center, University of Colorado Boulder, Boulder, Colorado v Atlantic Oceanographic and Meteorological Laboratory, Miami, Florida w Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey (Manuscript received 6 May 2013, in final form 22 November 2013) ABSTRACT In part III of a three-part study on North American climate in phase 5 of the Coupled Model Intercomparison Project (CMIP5) models, the authors examine projections of twenty-first-century climate in the representative concentration pathway 8.5 (RCP8.5) emission experiments. This paper summarizes and synthesizes results from several coordinated studies by the authors. Aspects of North American climate change that are examined include changes in continental-scale temperature and the hydrologic cycle, extremes events, and storm tracks, as well as regional manifestations of these climate variables. The authors also examine changes in the eastern North Pacific and North Atlantic tropical cyclone activity and North American intraseasonal to decadal variability, including changes in teleconnections to other regions of the globe. Projected changes are generally consistent with those previously published for CMIP3, although CMIP5 model projections differ importantly from those of CMIP3 in some aspects, including CMIP5 model agreement on increased central California precipitation. The paper also highlights uncertainties and limitations based on current results as priorities for further research. Although many projected changes in North American climate are consistent across CMIP5 models, substantial intermodel disagreement exists in other aspects. Areas of disagreement include projections of changes in snow water equivalent on a regional basis, summer Arctic sea ice extent, the magnitude and sign of regional precipitation changes, extreme heat events across the northern United States, and Atlantic and east Pacific tropical cyclone activity. Corresponding author address: Eric D. Maloney, Department of * Supplemental information related to this paper is available at Atmospheric Science, Colorado State University, 1371 Campus the Journals Online website: http://dx.doi.org/10.1175/JCLI-D- Delivery, Fort Collins, CO 80523-1371. 13-00273.s1. E-mail: [email protected] DOI: 10.1175/JCLI-D-13-00273.1 Ó 2014 American Meteorological Society Unauthenticated | Downloaded 10/05/21 07:28 PM UTC 15 MARCH 2014 M A L O N E Y E T A L . 2231 1. Introduction Tebaldi 2004; Diffenbaugh et al. 2005; Biasutti et al. 2012; Christiansen et al. 2011; Diffenbaugh and Scherer The twenty-first-century projections generated by 2011; Duffy and Tebaldi 2012; Lau and Nath 2012), phase 5 of the Coupled Model Intercomparison Project projected trends that are generally consistent with ob- (CMIP5; Taylor et al. 2012) are analyzed here to assess served trends in such quantities over the last century climate change in North America (NA). This study ac- (Alexander et al. 2006). Decreases in the duration of the companies two companion papers (Sheffield et al. 2013a, snowpack have been projected for many regions, in hereafter Part I; Sheffield et al. 2013b, hereafter Part II) particular low altitude areas of the Pacific Northwest that assess the CMIP5 models’ potential to accurately and Rockies (e.g., Brown and Mote 2009; Elsner et al. simulate regional climate in the twentieth century. 2010). Such changes are likely to lead to earlier spring Additionally, it provides an overview and is a first step snowmelt in many areas of the west (e.g., Hay et al. toward integrating the understanding of climate pro- 2011). While model agreement is good on projected jection results from the individual papers in the Journal overall snow water equivalent declines in many areas by of Climate special collection entitled ‘‘North American the end of the twenty-first century, some models show climate in CMIP5 experiments.’’ This paper first exam- increases in snowpack along the Arctic Rim by 2100 ines the changes in the continent-wide distribution of (e.g., Brown and Mote 2009), particularly at the height seasonal precipitation and temperature in simulations of the winter season, even though the length of the snow making use of representative concentration pathway season shortens (e.g., Rais€ anen€ 2008). 8.5 (RCP8.5; Taylor et al. 2012). It then focuses on a The projected response of NA climate in future select set of regional climate features. These changes are emission scenarios is often more nuanced on the re- considered in the context of the ability of models to gional and local scales than for the continental-scale accurately simulate current climate, discussed in the two features, especially when considering the evolution companion papers (Part I and Part II), which is generally during the seasonal cycle. For example, Rauscher et al. comparable to that of CMIP3 models, with some im- (2008) noted an earlier onset of the midsummer drought provement noted for individual models. in Mexico and Central America in model projections for Previous projections of NA climate change (e.g., the end of the twenty-first century. Previous studies CMIP3) have been evaluated as part of earlier climate project a redistribution of precipitation in monsoon assessments (Solomon et al. 2007). The CMIP3 con- regimes such as the southwest United States with re- sensus projection indicated that, by 2080–99, annual duced spring rainfall and increased late rainy season mean temperature increases are very likely across NA rainfall (Seth et al. 2010, 2011; Biasutti and Sobel 2009). with the greatest changes in northern Canada and Alaska, Ruiz-Barradas and Nigam (2010) showed that pro- where 108C mean wintertime temperature increases are jections for the twenty-first century indicate a wetter projected in some scenarios (Solomon et al. 2007). In- north-central United States during spring (increase creases in annual mean precipitation are projected for in number of extreme springs) and a drier southwest the northern tier of the United States, northward into United States but little consistency in summer rainfall Canada, with projected decreases for the southwest tendencies among models in these same regions. The United States, east Pacific warm pool, Caribbean, and uncertainty in projected summer precipitation extends adjacent land areas (e.g., Neelin et al. 2006; Seager et al. to adjacent land areas of the Gulf of Mexico (Biasutti 2007; Seager and Vecchi 2010). et al. 2012). Studies using CMIP3 projections suggest Beyond mean state changes, CMIP3 models predict a that, while the total number of North Atlantic tropical general increase in precipitation intensity (e.g., Diffenbaugh cyclones (TCs) will decrease and the number of intense et al. 2005; Mahajan et al. 2012), particularly in the hurricanes will increase, changes in North Atlantic TC northern tier of the United States and Canada (Tebaldi activity remain uncertain. This is likely because cli- et al. 2006). Increases in the duration and severity of mate models produce differing patterns of tropical drought are projected in regions such as Central America SST change and different representations of