Appendix B: Additional Climate-Related Factors Not Directly Modeled -- A Literature Review
SNAP’s climate data, while extensive, is limited to factors related to mean monthly temperature and
precipitation. However, other climate-related factors may also play key roles in the future of ecological
landscapes, natural resources and livelihoods in south-central Alaska. These factors include the Pacific
Decadal Oscillation (PDO), storms, extreme weather events, potential changes in sea level, glacial loss,
and ocean acidification, While this report cannot provide an exhaustive review of all of the above topics,
the overview below, based on the best available literature, provides a brief assessment of the roles
these factors may play, as well as feedbacks among them.
Pacific Decadal Oscillation (PDO)
Fluctuations in climate over a period of approximately one to three decades in the Gulf of Alaska region
and other parts of the state are tied to a pattern of variability known as the Pacific Decadal Oscillation
(PDO). The PDO is not directly linked to anthropogenic climate change, but can either exacerbate or
temporarily mask ongoing trends. Although other global patterns of atmospheric and oceanic variability
also affect the region, the PDO accounts for the most variance in modeled sea surface temperatures and
sea surface heights (Chhak et al. 2009). The PDO has major impacts on natural systems, including many
marine fisheries in the North Pacific. PDO fluctuations have been occurring at least as far back as 1750
(D’Arrigo et al. 1999). Several independent studies show that a cool PDO regime occurred from 18901924, a warm regime from 1925-1947, another cool spell from 1947-1976, and a warm PDO from 1977
through the mid-1990's (Mantua and Hare 2002). A current shift back to a cold cycle may mask climate
trends for the next few years.
Storms
The literature presents conflicting scenarios regarding recent and projected storm activity in the Gulf of
Alaska. These conflicting scenarios reflect continuing uncertainty about the complex role that global
climate has in warming ocean surfaces, and the unclear linkages between this warming and regional
storm patterns at annual, decadal, and longer time frames. Graham and Diaz (2001) found evidence
that North Pacific winter cyclones have been increasing since 1948. Specifically, they measured major
changes in cyclones in the Gulf of Alaska over a fifty-year time period, along with increases in extreme
wave heights. They attribute this change to increasing upper-tropospheric winds and vertical wind
shear, which are in turn linked to modulation of El Nino and increasing sea surface temperatures in the
western tropical Pacific. In contrast, Teng et al. (2008) predict decreases in cyclone activity in Alaska,
based on outputs from the CCSM3 model. Meanwhile, Mesquita et al. (2010) found that there was no
clear trend toward either increased or decreased storm frequency in the region. Sea surface
temperature did not appear to be a major driver of stroms in the Gulf of Alaska. They also noted that
summer storms tended to be longer than winter storms, and that the coastal orography of northwest
North America results in the Gulf of Alaska being the "graveyard'' of Pacific storms. Lee et al. (2012)
observed that North Pacific storm patterns moved into the Gulf of Alaska during the winter season after
the climate shift that took place in the late 1970s, but state that climatologists are still uncertain
regarding linkages between this type of shift and increases in tropical sea surface temperatures.
Extreme Weather Events
Extreme weather events include storms (discussed above) and associated high precipitation events;
extreme daily high and low temperature events; and prolonged periods of high or low temperature or
high or low rainfall (droughts). SNAP data captures these prolonged events, but does not necessarily
capture daily extremes.
If we can assume that the overall variability in weather (day-to-day fluctuations) is neither increasing nor
decreasing, and that variability in temperature and precipitation are approximately normally distributed,
then we can extrapolate future extreme values by coupling trends in mean values with historical
variability. For example, if mean January temperatures for a particular site are expected to increase
from -5°C to +1°C in the next 50 years, and if the standard deviation in daily values for January is 6°C,
then we can assume that historically, less than 2.5% of all January days exceeded temperatures of +7°C,
whereas 50 years from now, roughly 17% of all days will exceed this temperature.
However, if changes in the variability of temperature and precipitation are expected, then this algorithm
would not hold true. Whether this is occurring in the Gulf of Alaska is somewhat unclear, although the
general consensus appears to be that variability is showing modest increases. There are few available
datasets analyzing systematic changes in variability or extremes. Walsh et al. (2005) found little
evidence of increased variance of daily temperatures in Alaska between 1951 and 2000, despite an
increase in extreme daily temperatures from the 1950s to the 1990s. However, model projections
indicate increasing frequencies of record high daily temperatures over the course of the current century
(Timlin and Walsh 2007). Walsh et al. (2011) also note that increases in both storms and extreme
temperature events are evident across Alaska. However, it is not always clear whether these extreme
values indicate a change in mean values, a change in variability, or both.
Sea Level and Glacial Loss
In Alaska, potential sea level changes are inextricably linked to glacial loss, because in many areas the
effects of rising oceans is being offset by isostatic rebound (rising land masses as the weight of glacial ice
is removed). Mann et al. (1998) note that since the Holocene, sea level has often varied widely between
sites no more than 100km apart due to earthquakes and glacial fluctuations. However, uplift has been
the prevailing historical trend, and has allowed, for example, the preservation of a 7000 year
archaeological sequence along the coastline of Katmai National Park (Crowell and Mann 1996).
As with other climate-related variables, glacial data shows a clear trend, but incorporates significant
regional variability. A comprehensive analysis of Alaskan glaciers (Molnia 2007) used maps, historical
observations, ground-and-aerial photographs and satellite images, and vegetation data to determine
changes in glacial length and area (given lack of mass balance data). More than 98% of the glaciers
examined are currently retreating. However, in the Coast Mountains, St. Elias Mountains, Chugach
Mountains, and the Aleutian Range more than a dozen glaciers – mostly tidewater glaciers -- are
currently advancing and thickening. Arendt et al. (2006) argue that tidewater glaciers should be
considered separately, since their changes are largely independent of changes in climate. In a study
focused on the Chugach Mountains, they used airborne altimetry measurements to determine the
volume changes of 23 glaciers between 1950/1957 and 2001/2004. Average growth or loss ranged from
- 3.1 to 0.16 meters per year for the tidewater and - 1.5 to -0.02 meters per year for the nontidewater
glaciers. Chen et al. 2006 used satellite gravity measurements to assess glacial loss, and found a
prominent melting trend around the Gulf of Alaska.
As global sea levels continue to rise – with Alaska’s glaciers among the contributing sources (Hood et al.
2009) – it is unclear at what point rising water may overtake the effects of isostatic rebound.
Ocean Acidification
Anthropogenic atmospheric carbon causes increased carbon dioxide (Co2) in the oceans, resulting in
lower seawater pH, which in turn can inhibit the production of shell material. Increased acidity has
recently been documented in the northeast Pacific (Pfister et al. 2011).
Thus far, pteropods do not show declines in the north Pacific (Mackas and Galbraith 2012), although
modeling efforts predict declines in fishing success and marine biomass (Ainsworth et al. 2011).
Hopkinson et al. (2010) experimentally tested the effect of CO2 on growth and primary production under
iron-limited and iron-replete conditions in the high-nutrient, low-chlorophyll waters of the Gulf of
Alaska. Their results showed variable effects of CO2
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