Monitoring Change in the Arctic - Satellite-based Applications on Climate Change - page 124

Untersteiner 2011; Comiso 2012) and that changes are also evident in other climate
parameters such as surface air temperature, atmospheric circulation, precipitation,
snowfall, biogeochemical cycling, and vegetation (Curry et al. 1996 ; Wallace et al.
1996 ; Rigor et al. 2000 ; Groves and Francis 2002 ; Chapman andWalsh 1993 ;Myneni
et al. 1997 ;WangandKey 2003 ; Wang et al. 2012). A comprehensive reviewof recent
changes in the Arctic cryosphere (snow and ice) is available in AMAP ( 2011 ).
Numerous modeling studies have shown that the Arctic is one of the most
sensitive regions on Earth to global climate change due primarily to the positive
feedback between surface temperature, surface albedo, and ice extent, known as
the ice-albedo feedback (Manabe et al. 1992 ; Manabe and Stouffer 1994 ; Miller
and Russell 2000 ; Meehl and Washington 1990 ; Curry et al. 1996 ). This theory
of “polar amplification” has been confirmed by observational evidence, though
records of Arctic climate change are brief and geographically sparse. There are a
number of potential causes for Arctic climate change: changes in the large-scale
atmospheric circulation (e.g., Graversen et al. 2008 ; Overland 2009 ), the ice-albedo
feedback (Perovich et al. 2008 ), changes in greenhouse gas amounts and the
associated radiative forcing (Serreze et al. 2007 ; Graversen and Wang 2009 ) and
clouds (Liu et al. 2008 ; Kay and Gettelman 2009 ), and changes in ocean circulation
and the inflow of warm ocean water (Shimada 2006 ).
The Arctic, roughly defined here as the area poleward of 60 north latitude
(Fig. 9.1 ), has a complex climate system that is strongly influenced by both internal
processes and external forcings. Being one of the Earth's “heat sinks” (the other is
the Antarctic), atmospheric and oceanic heat and moisture fluxes dominate large-
scale Arctic climate patterns. Interactions between the ocean, atmosphere, and
cryosphere not only control local processes such as the surface energy budget but
also feed back to the global climate system. Changes in Arctic climate can have a
profound impact on midlatitude weather.
Monitoring the Arctic climate system requires accurate measurements of the
atmosphere, cryosphere, and ocean. This includes, but is not limited to, snow cover;
sea, lake, and land ice; cloud; atmospheric temperature and humidity structure; winds;
and sea surface temperature. Measurements of the following quantities are needed:
￿ Clouds: cover, thermodynamic phase, height, optical thickness, particle size
￿ Atmospheric temperature and humidity profiles
￿ Wind speed, direction, height
￿ Snow: extent (cover), snow water equivalent (SWE), depth
￿ Sea and lake ice: extent (cover), concentration, thickness, motion
￿ Surface temperature and albedo
These are not the only climate variables of interest, but they are the variables
that have significant impacts on climate, change on hourly to annual time scales,
and can be measured with sufficient accuracy from space. Other quantities for
which space-based remote sensing methods continue to be developed include
solid precipitation, permafrost characteristics, glaciers, ice sheets, and freshwater
ice. Table 9.1 lists the satellite sensors that can be used to estimate many of the
essential climate variables (ECVs) in the polar regions.