11
Susceptibility to a range of soil degradation processes is another cause of the depletion of SOC concentration and stock in soils of SSA. The SOC-related degradation
is set in motion by decline in soil structure, reduction in proportion and strength of
soil aggregates, crusting, compaction, decline in water infiltration, high runoff, erosion and non-point source pollution, and the attendant drought-flood syndrome.
Indeed, drought and flood are the two sides of the same coin. Thus, restoration and
judicious management of SOC concentration and stock is the most critical strategy
to reverse the degradation trends.
4 Impact of Climate Change
Climate is one of the five active factors of soil formation (Jenny 1941), and “human”
is now the sixth factor, hence the name “Anthrosols” (Bidwell and Hole 1965; Dudal
2004). Leopold (1949) stated that “Human beings are all interlocked with plants,
animals, soils and waters in one humming community of cooperation and competition: one biota. They are related and bound into a seamless fabric.” Indeed, soilclimate- human factors are intricately interlinked, and humanity’s impact on soil is
increasing with increase in population, affluence with which the population lives,
and changes in technologies. Thus far, from the onset of agriculture about 10–12 millennia ago till now, the impact of humanity on climate and soil has been negative
because both of these resources have been taken for granted. Indeed, climate and
soil, considered and used as global commons, are prone to the tragedy of commons
and are a phenomenon of the Anthropocene (Lal 2007b).
Global abundance of greenhouse gases (GHGs) in 2017 was 405.5 ppm for
carbon dioxide (CO 2 ), 1859 ppb for methane (CH 4 ), and 329.9 ppb for nitrous
oxide (N 2 O) (Lal 2018a; WMO 2019).The atmospheric concentration of CO 2
attained the value of 415.6 ppm during May 2019 (NOAA-ESRL 2019). Carbon
dioxide levels at present are more than those at any time during the past
800,000 years (Lindsey 2018). Three principal sources of emission of GHGs are
fossil fuel combustion, tropical deforestation, and accelerated soil erosion. For the
decade of 2008–2017, annual average emissions were 9.4 ± 0.5 Pg C/year from
fossil fuel combustion and 1.5 ± 0.7 Pg C/year from tropical deforestation. Of
this, 4.7 ± 0.02 Pg C/year was absorbed by the atmosphere, 2.4 ± 0.5 Pg C/year by
the ocean, and 3.2 ± 0.8 Pg C/year by the land-based sinks with a budget imbalance of 0.5 Pg C/year (Le Quéré et al. 2018). For the year 2017, emission was
9.9 ± 0.5 Pg C/ year from fossil fuel combustion and 1.4 ± 0.7 Pg C/ year from
tropical deforestation. In comparison, uptake by different sinks was 4.6 ± 0.2 Pg
C/year by the atmosphere, 2.5 ± 0.5 Pg C /year by the ocean, and 3.8 ± 0.8 Pg C /
year by the land-based sinks, with a budget imbalance of 0.3 Pg C (Le Quéré et al.
2018). Thus, the anthropogenic activities have approximately caused global
warming of 1.0 °C above the pre-industrial level (with a range of 0.8–1.2 °C).
Further, with the business-as-usual attitude, global warming is likely to reach
1.5 °C between 2030 and 2052 (IPCC 2018).
Agricultural and Natural Resource Sustainability Under Changing Climate in Africa
Susceptibility to a range of soil degradation processes is another cause of the depletion of SOC concentration and stock in soils of SSA. The SOC-related degradation
is set in motion by decline in soil structure, reduction in proportion and strength of
soil aggregates, crusting, compaction, decline in water infiltration, high runoff, erosion and non-point source pollution, and the attendant drought-flood syndrome.
Indeed, drought and flood are the two sides of the same coin. Thus, restoration and
judicious management of SOC concentration and stock is the most critical strategy
to reverse the degradation trends.
4 Impact of Climate Change
Climate is one of the five active factors of soil formation (Jenny 1941), and “human”
is now the sixth factor, hence the name “Anthrosols” (Bidwell and Hole 1965; Dudal
2004). Leopold (1949) stated that “Human beings are all interlocked with plants,
animals, soils and waters in one humming community of cooperation and competition: one biota. They are related and bound into a seamless fabric.” Indeed, soilclimate- human factors are intricately interlinked, and humanity’s impact on soil is
increasing with increase in population, affluence with which the population lives,
and changes in technologies. Thus far, from the onset of agriculture about 10–12 millennia ago till now, the impact of humanity on climate and soil has been negative
because both of these resources have been taken for granted. Indeed, climate and
soil, considered and used as global commons, are prone to the tragedy of commons
and are a phenomenon of the Anthropocene (Lal 2007b).
Global abundance of greenhouse gases (GHGs) in 2017 was 405.5 ppm for
carbon dioxide (CO 2 ), 1859 ppb for methane (CH 4 ), and 329.9 ppb for nitrous
oxide (N 2 O) (Lal 2018a; WMO 2019).The atmospheric concentration of CO 2
attained the value of 415.6 ppm during May 2019 (NOAA-ESRL 2019). Carbon
dioxide levels at present are more than those at any time during the past
800,000 years (Lindsey 2018). Three principal sources of emission of GHGs are
fossil fuel combustion, tropical deforestation, and accelerated soil erosion. For the
decade of 2008–2017, annual average emissions were 9.4 ± 0.5 Pg C/year from
fossil fuel combustion and 1.5 ± 0.7 Pg C/year from tropical deforestation. Of
this, 4.7 ± 0.02 Pg C/year was absorbed by the atmosphere, 2.4 ± 0.5 Pg C/year by
the ocean, and 3.2 ± 0.8 Pg C/year by the land-based sinks with a budget imbalance of 0.5 Pg C/year (Le Quéré et al. 2018). For the year 2017, emission was
9.9 ± 0.5 Pg C/ year from fossil fuel combustion and 1.4 ± 0.7 Pg C/ year from
tropical deforestation. In comparison, uptake by different sinks was 4.6 ± 0.2 Pg
C/year by the atmosphere, 2.5 ± 0.5 Pg C /year by the ocean, and 3.8 ± 0.8 Pg C /
year by the land-based sinks, with a budget imbalance of 0.3 Pg C (Le Quéré et al.
2018). Thus, the anthropogenic activities have approximately caused global
warming of 1.0 °C above the pre-industrial level (with a range of 0.8–1.2 °C).
Further, with the business-as-usual attitude, global warming is likely to reach
1.5 °C between 2030 and 2052 (IPCC 2018).
Agricultural and Natural Resource Sustainability Under Changing Climate in Africa