Past, Present, and Future Climate Change: Can Palaeoecology Help Manage a Warming World? - Biodiversity Conservation and Environmental Change - page 97

palaeo environmental record provides vital information on quantifying the effects of land
cover-climate feedbacks, aiding the development of more realistic climate-vegetation simu-
lations, and thus improving our capacity to predict the effects of future climate change. The
modelling and palaeoecology together have demonstrated the likely non-linear response of
the Sahara desert to changing climate. More complex models that include feedbacks between
climate and landcover illustrate how rapid and abrupt changes in vegetation can occur, even
though orbital insolation was increasing gradually (Demenocal et al. 2000, Cole et al. 2009,
Krinner et al. 2012). In the mid-Holocene, orbital forcing changed gradually, but vegetation
tipped relatively abruptly into a green state, and remained resilient for several thousand
years, even when orbital factors had diminished.
This tipping point between desert and green stable states holds important information
about how vulnerable the Sahara and Sahel are to future changes in the North Atlantic mon-
soon. If warmer climates of the mid-Holocene led to increasing water availability in North
Africa, could the Sahara become green again in the future? Simulations by a global coupled
climate model that includes insolation and atmospheric CO 2 and CH 4 concentrations, shows
that both 'green' and 'desert' Sahara alternate stable states were possible between 7,500 and
5,500 years ago (deMenocal et al. 2000, Renssen et al. 2003, 2006). Under present-day insola-
tion, only the desert state is possible, but this may change; the simulation suggests that a
'green Sahara' may be possible in the future if CO 2 continues to rise and the predicted increase
in rainfall occurs (Renssen et al. 2006, Lézine et al. 2011).
Effects of warmer climates on socioecological systems
Studies of the effects of declining vegetation cover in the Sahara, and aridification of the Alti-
plano (see earlier) show the important interactions between environmental change and
socio-ecological adaptations; populations responded to aridification through changes in
livelihood strategy, settlement patterns, changes in governance, and technological innov-
ations such as the development of irrigation systems (Bard 2013). The effects of warmer cli-
mates on societies vary dramatically in different places, depending on the interacting effects
of rainfall and temperature, and whether food production is temperature or rainfall limited.
As a result, some societies survived and flourished during past warm periods, while others
perished.
The complex interactions between climate change and societal adaptations highlight
the importance of effective water management and resilient agricultural systems in times
of rapid environmental change. For example, warm, wet summers contributed to rising
prosperity in central Europe during the RWP, contributing to the expansion of the Roman
Empire and facilitating economic connections throughout the Mediterranean and near
East (Büntgen et al. 2011, Drake 2012). Subsequently, erratic rainfall from 250-600 ce and
the failure of wheat crops, contributed to the fall of the Western Roman Empire, trigger-
ing waves of migration, invasions, political instability, and social turmoil (Büntgen et al.
2011). Recent studies have shown that wheat and maize production may decrease