The State of Circumpolar Walrus Populations

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Climatic warming could also have unanticipated impacts. For example, an increase in the
occurrence of thunderstorms could disturb walruses and result in stampede-related mortality
(Okonek and Snively 2005). If primary prey species become limited, walruses might eat more
seals and thereby increase the incidence of Trichinella infection (Garlich-Miller et al. 2011)
although the life history of T. nativa is not well known.
Potential for future habitat projections
Predictions of future conditions can be an important tool for identifying conservation priorities
for circumpolar walrus populations. We therefore explored the possibility of projecting future
habitat based on two Representative Concentration Pathways (RCPs) - 8.5 and 4.5 - as identified
by the Intergovernmental Panel on Climate Change (IPCC).
Representative Concentration Pathways (RCPs) are four greenhouse gas concentration
trajectories adopted by the IPCC for its fifth Assessment Report (AR5) in 2014 (Moss et al. 2008,
2010). The pathways are used for climate modelling and research and describe four possible
climate futures that depend on the quantity of greenhouse gas emissions in future years. The four
RCPs are RCP 2.6, RCP 4.5, RCP 6, and RCP 8.5, which are named after a possible range of
radiative forcing values in the year 2100 relative to pre-industrial values (+2.6, +4.5, +6.0, and
+8.5 W/m 2 , respectively) (Weyant et al. 2009). The RCPs are consistent with a wide range of
possible changes in future anthropogenic greenhouse gas (GHG) emissions (van Vuuren et al.
2011; Collins et al. 2013). The different scenarios have the following assumptions on global
annual GHG emissions (Meinshausen et al. 2011): RCP 2.6 assumes that emissions peak between
2010-2020 and decline substantially thereafter; emissions in RCP 4.5 peak around 2040 and then
decline; compared to RCP 6 where emissions peak around 2080, then decline; and RCP 8.5,
where emissions continue to rise throughout the 21st century (i.e., a worst-case scenario). Each
RCP was developed by a different modelling group.
Two of the four scenarios are being considered. RCP 4.5 is an intermediate emissions scenario
developed by the Pacific Northwest National Laboratory in the US. In this scenario radiative
forcing is stabilized by 2100, consistent with a future with relatively ambitious emissions
reductions, stringent climate policies, stable methane emissions, and CO2 emissions that continue
to increase only slightly before a decline commences ca. 2040 (Thomson et al. 2011). In contrast,
RCP 8.5 is a high emission scenario developed by the International Institute for Applied System
Analysis in Austria. It is consistent with a future with no policy changes to reduce emissions and
is characterized by increasing greenhouse gas emissions that lead to high greenhouse gas
concentrations over time (Riahi et al. 2011).