Page 10 - Perspective Paper

3 Reciprocity between land cover and climate

On a planetary scale, anthropogenic forcing has led to a persistent imbalance in the global mean top-of-
atmosphere radiation budget (Forster et al., 2021). Perturbations in the radiation budget alters the global
mean temperature, rainfall patterns and climate extremes (Pörtner et al., 2022). The burning of fossil fuels
and subsequent rising CO2 levels as the main cause of climate change has become conventional wisdom
among scientists and policy makers, and has led to a carbon focus for climate mitigation strategies all over
the globe. However, the exclusive focus on greenhouse gas (GHG) emissions as the only cause of climate
change has distracted us from another major climate-impacting development that has occurred
synchronously, namely land use change. Over the past 10,000 years, but particularly the past 3000 years, we
have altered vast areas of terrestrial surfaces by clearing forests and expanding agriculture (Ellis, 2021),
enough to degrade up to 40% of Earth’s surface, according to the UNCCD (UNCCD, 2022). This has greatly
altered the capacity of the land surface to infiltrate/retain rainfall, protect soils from solar radiation/erosion
and contribute to the water/energy cycles via evapotranspiration and cloud formation (Anthes, 1984;
Lawrence et al., 2022; Seneviratne et al., 2010). Whilst recognizing CO2 emissions should be cut back, devising
all climate change solutions within the carbon math paradigm will likely fall short in the long term. The state
of the climate is not only a function of GHG, but also of water and radiant energy. These are biologically-
mediated, interrelated cycles, and deploying only carbon-sequestering technology or reduction strategies
will not restore the natural climate-regulating capacity of the biosphere.

3.1 The climate regulating role of the biosphere

The biosphere includes all life on Earth. The different components of the biosphere have co-evolved with the
land, atmosphere and oceans and together govern the state of the climate through regulating the carbon,
water and radiant energy cycles (Gettelman & Rood, 2016). This includes a climate in which life on Earth
(including humans) has evolved and continue to depend on for their existence. The physical and ecological
processes of the biosphere are driven by the energy from the Sun. Incident solar energy that reaches Earth’s
atmosphere (insolation) will either reflect back to space (depending on clouds, aerosols or atmospheric
composition), be absorbed by the atmosphere or penetrate through and reach Earth’s surface directly. After
which this radiation is reflected or absorbed depending on albedo, which is determined by the colour/texture
of the land surface (Spellman, 2017). Upon absorption at the surface, solar energy undergoes a
transformation in which biosphere largely governs the flux of energy between the surface and the
atmosphere (Gerten et al., 2004). In particular, the biosphere plays an important role in the partitioning of
latent and sensible heat (the Bowen ratio), which determines the amount of evapotranspiration and the
temperature at the surface (Moon et al., 2020).
Evapotranspiration refers to the process by which water moves from Earth’s surface to the atmosphere
through soil evaporation and plant transpiration. Globally this process consumes more than half of the
incoming radiant energy (Trenberth et al., 2009). Vegetation is the primary factor affecting
evapotranspiration, as 59% of global evapotranspiration comes from terrestrial plant transpiration (Wang-
Erlandsson et al., 2014). These exchanges and interactions between the biosphere and atmosphere regulate
the hydrological cycle, govern the heat dynamics of the Earth and together produce the climate patterns we
know today (te Wierik et al., 2021).

Land-atmospheric interactions in the form of water and energy exchanges occur at the atmospheric
boundary layer (ABL), which marks the interface between these two spheres and largely influence global
weather and climate patterns (Santanello et al., 2018). Changes in land surface affect its roughness
properties, which, in turn, govern the degree of albedo and evapotranspiration coming from it (Perugini et
al., 2017). Changes in evapotranspiration mediate the energy and water balance of the atmosphere and can
influence local and regional climate and temperature (Wang-Erlandsson et al., 2022). For example, changes

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