Page 6 - Perspective Paper

2 Degradation in Northern Africa: a multi-causal phenomena

The timing, rate and direction of climate change is the cumulative result of natural variability, anthropogenic
forcing and the resultant terrestrial-atmospheric feedbacks. Palaeoclimatological records indicate a strong
relation between the Earth’s orbital parameters (Milankovitch cycles) and the planetary climate conditions
(Pausata et al., 2020). Since the beginning of the Pleistocene 2.6 million years ago, there have been over 20
ice ages driven by orbital changes, which have had significant effects on global climates extending to the
equatorial regions (Crucifix, 2012; Herbert et al., 2010). However, climate variations throughout history
cannot be explained by Milankovitch cycles alone. The general conclusion of long-term ecological research
shows that shifting regimes are always multi-causal (Foley et al., 2013) and the role of anthropogenic forcing
in driving continental-scale changes to land cover may have been much more significant than previously
understood (Boivin et al., 2016; Hoag & Svenning, 2017; Wright, 2017). The profound potential of humans
to reduce vegetal biomass is not restricted to the post-industrial era, but rather dates back far into prehistory,
a period some call the Palaeoanthropocene: ‘the time interval before the industrial revolution during which
anthropogenic effects on landscape and environment can be recognized, but before the burning of fossil
fuels produced a huge crescendo in anthropogenic effects’ (Foley et al., 2013). This hypothesis further claims
humans have actively and interdependently co-evolved with their landscapes in the form of ‘niche
construction’ in which organisms’ trophic behaviours correspondingly shape the ecosystems they inhabit
(Braje & Erlandson, 2013; Glikson, 2013; Thompson et al., 2021). Decoupling the interplay of human agency
in shaping the environment is laden with uncertainty. This all begs the question: What is the ‘natural’ climate
and what role does humanity play in shaping planetary functioning over longue-durée timescales?

Socio hydrological interactions in the form of land-use change touch upon all green water variables –
terrestrial precipitation, evaporation and soil moisture. Land-use change alters precipitation patterns
through the modification of the local land–atmosphere coupling and large-scale circulation patterns (Pitman
et al., 2012; Runyan et al., 2012; Wang-Erlandsson et al., 2018). As for evaporation – agriculture and pasture
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expansions (now covering almost half Earth’s ice-free land area) has estimated effects of 2,000–3,000 km /yr
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decreases and 800–2,600 km /yr increases in evaporation – as a result of deforestation and irrigation,
respectively (Gordon et al., 2005). Soil moisture functions as the interface between precipitation and
evaporation, which implies that changes in soil moisture retention and availability to plants could generate
non-linear ecological, biogeochemical and atmospheric changes across scales (Wang-Erlandsson et al., 2022).

In all efforts to restore or regenerate ecosystems we ought to be aware of the root causes and potentially
amplifying feedbacks that lead the changing of landscapes and the inherit uncertainties therein. In this light,
although regreening efforts can have desirable effects for climate mitigation and biodiversity, afforestation
initiatives are still widely criticised. One major criticism that came from global analyses (e.g., Bastin et al.,
2019) is that those new forests are planned on places which have always supported other ecosystems with
their own functioning and biodiversity. This criticism emphasizes the necessity of conducting complementary
historical analyses of changing ecosystems including the dynamics of their functioning and the degree of
human agency in inducing regime shifts. Moreover, restoration action must assess the feasibility of
intentionally inducing ecological regime shifts and the associated (regional and global) impacts of doing so.

2.1 Palaeoclimatological and geomorphological signs of degradation

Degradation is defined in this report as the negative trend in land condition, including the loss of at least one
of the following: biological productivity, ecological integrity, or value to humans (Olsson et al., 2019). Like
many other deserts on Earth, the Sahara (which in biofunctionality includes the Sinai Peninsula) have
witnessed much wetter conditions in the past. Natural variation in insolation, combined with various other
mechanisms, gives rise to alternating arid and humid periods in North Africa, shifting approximately every

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