1 Space-Based Observations for Understanding Changes in the Arctic-Boreal 2 System: The Foundation for Coordinated Scientific Research and Informed 3 Decision-Making on Human Welfare, Environmental Health, Economic 4 Development, Adaptation, and Geostrategy 5 Bryan N. Duncan1, (in alphabetical order) James B. Abshire1, Ludovic Brucker1,2, James Carton3, 6 Josefino C. Comiso1, Emmanuel P. Dinnat1,4, Bruce C. Forbes5, Alemu Gonsamo6, Watson W. 7 Gregg1, Dorothy K. Hall7, Iolanda Ialongo8, Randi Jandt9, Ralph A. Kahn1, Alexey Karpechko8, 8 Stephan R. Kawa1, Timo Kumpula10, Erkki Kyrölä8, Tatiana V. Loboda11, Kyle C. McDonald12, 9 Paul M. Montesano1,13, Ray Nassar14, Christopher S. R. Neigh1, Lesley E. Ott1, Claire L. 10 Parkinson1, Benjamin Poulter1, Jouni Pulliainen8, Kimmo Rautiainen8, Brendan M. Rogers15, 11 Cecile S. Rousseaux1,2, Amber J. Soja16,17, Nicholas Steiner12, Johanna Tamminen8, Maria A. 12 Tzortziou1,12, James S. Wang1,2, Jennifer D. Watts15, David M. Winker17, Dong L. Wu1 13 14 1NASA Goddard Space Flight Center, Greenbelt, Maryland, USA 15 2Universities Space Research Association, Goddard Earth Sciences Technology and Research 16 Studies and Investigations, Columbia, Maryland, USA 17 3Department of Atmospheric and Oceanic Science, University of Maryland, College Park, 18 Maryland, USA 19 4CEESMO, Chapman University, Orange, California, USA 20 5Arctic Centre, University of Lapland, Rovaniemi, Finland 21 6University of Toronto, Toronto, Ontario, Canada 22 7Earth System Science Interdisciplinary Center, University of Maryland, College Park, 23 Maryland, USA 24 8Finnish Meteorological Institute, Helsinki, Finland 25 9Alaska Fire Science Consortium, University of Alaska, Fairbanks, Alaska, USA 26 10Department of Geographical and Historical Studies, University of Eastern Finland, Joensuu, 27 Finland 28 11Department of Geographical Sciences, University of Maryland, College Park, Maryland, USA 29 12City University of New York, The City College of New York, New York, NY, USA 30 13Science Systems and Applications, Inc., Lanham, Maryland, USA 31 14Climate Research Division, Environment and Climate Change Canada, Toronto, Ontario, 32 Canada 33 15Woods Hole Research Center, Falmouth, Massachusetts, USA 34 16National Institute of Aerospace, Hampton, Virginia, USA 35 17NASA Langley Research Center, Hampton Virginia, USA 36 37 Corresponding author: Bryan N. Duncan ([email protected]) 38 39 Key Points: 40 • we review the strengths and limitations of current space-based observational capabilities 41 for several important Arctic-Boreal System components 42 43 1 44 Abstract. Satellite and other observations taken over the last few decades indicate that dramatic 45 changes are occurring in the Arctic-Boreal Zone (ABZ), which are having significant impacts on 46 ABZ inhabitants, infrastructure, flora and fauna, and economies. There are unique challenges in 47 observing all the properties of the Arctic-Boreal System (ABS) -- which includes the cryosphere, 48 biosphere, hydrosphere, and atmosphere -- that are necessary to adequately monitor these 49 changes and to gain a process-based understanding of the factors that drive ABS changes, 50 including the interactions between ABS components. Therefore, we recommend a 51 comprehensive, yet practical, ABS observing strategy that will provide the necessary data to 52 monitor ABS changes, accurately predict future changes, and develop informed adaptation and 53 mitigation strategies. In this article, we review the strengths and limitations of current space- 54 based observational capabilities for several important ABS components and propose some 55 observational needs, including for the development and evaluation of ABS processes in Earth 56 System models, which may be met from space-based platforms. We strongly advocate for a more 57 robust surface observing network to complement satellite data and also to aid the evaluation of 58 space-based observations. Finally, we recommend that Earth scientists work closely with 59 stakeholders so that ABS data are properly used in decision-making, such as adaptation and 60 mitigation strategy development. 61 62 2 63 Contents 64 1 Introduction ................................................................................................................................................ 4 65 2 Surface Temperature: A Driver of Change (Josefino C. Comiso) ............................................................. 7 66 3 Observing Properties of the Cryosphere .................................................................................................. 10 67 3.1 Sea Ice (Claire L. Parkinson) ............................................................................................................ 10 68 3.2 Land Ice (Ludovic Brucker) ............................................................................................................. 13 69 3.3 Mapping Seasonal Snow Cover in the ABZ (Dorothy K. Hall) ....................................................... 16 70 3.4 Permafrost (Jouni Pulliainen, Kimmo Rautiainen) ........................................................................... 21 71 4 Observing Properties of the Oceans ......................................................................................................... 24 72 4.1 Ocean Salinity, Temperature and Circulation (Emmanuel P. Dinnat, James Carton) ...................... 24 73 4.2 Ocean Biology and Biogeochemistry (Cecile S. Rousseaux, Watson W. Gregg, Maria A. Tzortziou) 74 ................................................................................................................................................................ 28 75 5 Observing Properties of the Land Biosphere ........................................................................................... 30 76 5.1 Tundra Vegetation: Drivers, Feedbacks and Indicators of Systemic Change (Bruce C. Forbes, Timo 77 Kumpula) ................................................................................................................................................ 30 78 5.2 Boreal Vegetation (Brendan M. Rogers, Alemu Gonsamo, Paul M. Montesano, Christopher S. R. 79 Neigh, Jennifer D. Watts) ....................................................................................................................... 34 80 5.3 Wildfires: An Agent of Rapid ABZ Change (Amber J. Soja, Tatiana V. Loboda, Randi Jandt) ..... 39 81 5.4 Wetlands (Ben Poulter, Nicholas Steiner, Kyle C. McDonald) ........................................................ 44 82 6 Observing Properties of the Atmosphere ................................................................................................. 48 83 6.1 Short-lived Pollutants (Ralph A. Kahn, Bryan N. Duncan) .............................................................. 48 84 6.2 Long-Lived Greenhouse Gases (Bryan N. Duncan, Stephen R. Kawa, James B. Abshire, James S. 85 Wang, Lesley E. Ott, Ray Nassar) .......................................................................................................... 52 86 6.3 Clouds (Dong Wu) ............................................................................................................................ 56 87 6.4 Surface Ultraviolet Radiation and Stratospheric Ozone (Johanna Tamminen, Erkki Kyrölä, Alexey 88 Karpechko) ............................................................................................................................................. 58 89 7 ABZ Satellite Observing Strategies (Ray Nassar) ................................................................................... 61 90 8 Summary .................................................................................................................................................. 63 91 References ................................................................................................................................................... 64 92 93 3 94 1 Introduction 95 Numerous Earth science observations (e.g., surface temperature, sea ice extent and 96 thickness, snow cover extent and seasonality, ocean color, fire regimes, and ice sheet mass) 97 indicate long-term changes are occurring in the Arctic-Boreal Zone (ABZ; e.g., Comiso and 98 Hall, 2014; Richter-Menge et al., 2016), a region that lies north of approximately 50°N and 99 includes the boreal, sub-Arctic, and Arctic climate zones (Figure 1). In fact, ABZ surface 100 temperatures have warmed over twice as fast as the Earth as a whole over recent decades 101 (USGCRP, 2017) and the Arctic experienced the warmest average winter surface air temperature 102 on record in 2015-2016 (e.g., Cullather et al., 2016; Boisvert et al., 2016), which led to record 103 low winter sea ice extent (Ricker et al., 2017). The Arctic Monitoring and Assessment 104 Programme’s (AMAP) Snow, Water, Ice and Permafrost in the Arctic (SWIPA) assessment 105 (AMAP, 2017) summarizes these long-term ABZ changes, which are having profound and 106 complex effects on ABZ inhabitants and their welfare, flora/fauna, and economies (e.g., Larsen 107 et al., 2014; Arctic Council, 2016; USGCRP, 2017). Consequently, these changes have captured 108 the attention of ABZ countries, leading to efforts, such as the formation of the intergovernmental 109 Arctic Council in 1996, to coordinate and cooperate on common ABZ issues. 110 111 Figure 1. A true color image from the NASA Aqua/Moderate Resolution Imaging Spectroradiometer (MODIS) taken on June 28, 2010. The image captures many of the important ABZ components, including