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«Published: 01/01/2015 Link to publication Citation for published version (APA): Ardö, J. (2015). Soil carbon sequestration and climate change in ...»

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Soil carbon sequestration and climate change in semi-arid Sudan

Ardö, Jonas

Published in:

Sudan Academy of Sciences Journal-Special Issue (Climate Change)

Published: 01/01/2015

Link to publication

Citation for published version (APA):

Ardö, J. (2015). Soil carbon sequestration and climate change in semi-arid Sudan. Sudan Academy of Sciences

Journal-Special Issue (Climate Change), 11, 140-163.

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Download date: 16. Nov. 2016 Ardö, Sudan Academy of Sciences Journal-Special Issue (Climate Change), Vol. 11, 2015, 140-163 ISSN 1816-8272 Copyright © 2015 SAPDH Soil Carbon Sequestration and Climate Change in Semi-arid Sudan Jonas Ardö1 Abstract Climate change poses risk for natural and human systems in Africa. Increasing temperatures and changes in precipitation patterns is likely to affect agriculture, pastoralism and forestry. Mitigation of increasing atmospheric concentration of CO2 through soil carbon sequestration in semi-arid ecosystems may be beneficial to soil properties and cultivation. This paper describes and discusses soil carbon sequestration in relation to climate change in semi-arid regions, with special attention to the Sudan. It is anticipated that adaptation to climate changes is a more reasonable way to cope with future climate change than mitigation through soil carbon sequestration, especially for low emitting countries in Africa such as the Sudan.

Keywords: Adaptation, GHGs, Climate Change, Mitigation Introduction The increase of CO2 and other greenhouse gases (GHGs) in the atmosphere are very likely to impact future climate through increasing temperatures and changes in precipitation patterns and magnitudes. This will alter the general conditions for agriculture, forestry and similar activities directly depending on „weather‟ or climate. Marginal areas such as semi-arid regions are expected to be strongly affected by climate change as they are already affected by strong natural climatic fluctuations (mainly precipitation) that impact prosperity of self-supporting populations.

The term climate change has different meanings in different contexts. According to IPCC, climate change refer to “any change in climate over time, whether due to natural variability or as a result of human activity” (IPCC, 2014). United Nations Framework Convention on Climate Change (UNFCCC), on the other hand, defines climate change as “a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods” (UNFCCC, 2014). The recent IPCC fifth assessment report (AR5) describes and summarizes the state of the art of the current knowledge on the physical science basis of climate change (IPCC, 2013a), as well as the probabilities for various phenomena. The report combines a qualitative level of confidence for evaluation of the underlying scientific understanding and uses quantified probabilistic likelihoods when possible, to describe the degree of evidence for key findings (IPCC, 2013b).

Two major strategies to cope with climate changes are often considered, adaptation and mitigation (a third option, to deny or ignore that climate change occur at all, exists, but this is not based on scientific principles (Dunlap and 1 Department of Physical Geography and Ecosystem Science, Lund University Sölvegatan 12, 22362 Lund, Sweden, Jonas.Ardö@nateko.lu.se, 31 March 2014.

140 Ardö, Sudan Academy of Sciences Journal-Special Issue (Climate Change), Vol. 11, 2015, 140-163 McCright, 2011; Wikipedia, 2014)). Climate change mitigation includes actions taken to reduce the sources or enhance the sinks of GHGs. Climate change adaptation includes actions taken to decrease the effects or vulnerability of anthropogenic and biological systems to climate change effects. It is defined by UNFCCC as “Adjustment in natural or human systems in response to actual or expected climatic stimuli or their effects, which moderates harm or exploits beneficial opportunities”.

Carbon sequestration is the process of removing carbon (C) from the atmosphere and depositing it in a reservoir (UNFCCC, 2014) such as soil or biomass. It is hence mainly, but not only, a mitigating action. Carbon sequestered in soils or in vegetation is only temporarily removed from the carbon cycle. Residence times vary among carbon pools (soil, vegetation, atmosphere, oceans) and, hence will the sequestered carbon continue its flow as part of the carbon cycle after some time. This time is dependent on the abiotic and biotic environments, management, as well as other factors. The magnitude of these fluxes is also strongly influenced by the climate and can provide feedbacks on the climate system (IPCC, 2014;

Arneth et al., 2010).

This paper briefly describes, discusses and exemplifies experiences gained from studies of soil carbon sequestration and carbon cycle studies in semi-arid Africa with focus on the Sudan. The presented material is a combination of results from finished and current research projects as well as from selected scientific literature within the field.

1. Climate change IPCC states that “Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased” (IPCC, 2013a). The global average temperature have increased

0.78 °C when comparing the 1850–1900 period with the 2003–2012 period and almost the entire globe has experienced surface warming (IPCC, 2013a). Due to natural variability, trends calculated on short time series describing surface temperature are very sensitive to start and end time of these time series and robust multi-decadal data sets are needed. Most reports agree on the global warming, however a recent report mentions that the warming has taken “a pause” since 1998, and the increase in the global surface temperature from 1998 until 2013 is only 0.04 °C per decade from observations, but 0.21 °C per decade from recent simulations (Tollefson, 2014). This temporary reduction in temperature increase (Santer et al., 2014) should not be interpreted as a reduction of the changes in the climate. Out of the 14 warmest years since 1850 have 12 that occurred during the 21th century and for the north hemisphere is the latest 30 year period probably the hottest since the 15th century (IPCC, 2013a). Changes in precipitation are less confident and both positive and negative changes occur.

Extreme weather and climate events have been observed since about 1950. On the global scale, it is very likely that the number of cold days and nights has decreased and the number of warm days and nights has increased (IPCC, 2013a).

141 Copyright © 2015 SAPDH ISSN 1816-8272 Ardö, Sudan Academy of Sciences Journal-Special Issue (Climate Change), Vol. 11, 2015, 140-163 There are likely more land regions where the number of heavy precipitation events has increased than where it has decreased.

The main cause of the observed climatic changes is attributed to the increase of GHGs in the atmosphere. The atmospheric concentrations of CO 2, CH4 and N2O are higher today than they had been during the last 800,000 years (IPCC, 2013a).

The mean rates of increase are the highest in 22,000 years. The major sources of CO2 include emissions from fossil fuel burning and cement production yielding a source of 9.5 Gt C yr–1 in 2011. The annual net increase of CO2 due to anthropogenic land use change was estimated at 0.9 Gt C yr –1 (average for 2002The increase of CO2 makes the total radiative forcing positive and cause an uptake of energy in the climate system. The total radiative forcing has increased with a factor of 2.29 as compared to the 1750 level (IPCC, 2013a).

A waste majority of the scientific community agree that there is a casual relationship between the release of GHGs and increasing temperatures (IPCC, 2013b; Anderegg, 2010; Doran and Zimmerman, 2009; Oreskes, 2004; NASA, 2014). A recent investigation concludes that “the number of papers rejecting the consensus on anthropogenic global warming is a vanishingly small proportion of the published research” (John et al., 2013) and the AR5 also states that “human influence on the climate system is clear” (IPCC, 2013b).

The large amount of scientific literature concerning climate change is demanding to survey but an up to date summary is given in the fifth IPCC assessment report whereof the working group 1 (The Physical Basis) report (IPCC, 2013a) is already available and the reports of working group 2 (Impacts, Adaptation and Vulnerability) and 3 (Mitigation of Climate Change) will be released during the spring of 2014 and will be available at http://www.ipcc.ch/.

We find support for anthropogenic climate changes, mainly attributed to emissions of GHGs originating from the developed world and with a tendency to affect the developing world, not at least Africa (Toulmin, 2009).

Africa IPCC fourth assessment report states that “Africa is one of the most vulnerable continents to climate change and climate variability, a situation aggravated by the interaction of „multiple stresses occurring at various levels and low adaptive capacity” (Boko et al., 2007), and it points out the high vulnerability of Africa‟s major economic sectors to current climate change. This vulnerability is due to the already limited water supply, poverty, ecosystem degradation, complex disasters and conflicts, among other causes. The adaptive capacity is considered weak, further increasing the vulnerability to climate change. Water stress may increase due to changes in precipitation, rainfall intensity and increased evaporation in combination with an increased demand for water. The proportion of arid and semi-arid regions is likely to increase by 5-8% (Boko et al., 2007).

Minimum temperatures have been observed to increase slightly faster than maximum and mean temperatures (Boko et al., 2007). The number of warm spells over western and southern Africa has increased and a decrease in the number of very cold days has been reported (New et al., 2006). The recent IPCC fifth assessment report shows significant temperature increases for all of Africa (1901whereas some areas are uncertain due to incomplete or missing data (IPCC, 142 Copyright © 2015 SAPDH ISSN 1816-8272 Ardö, Sudan Academy of Sciences Journal-Special Issue (Climate Change), Vol. 11, 2015, 140-163 2013b).The density of the network of climate stations in Africa is low, averaging one station per 26000 km2, eight times lower than the WMO's (World Meteorological Organization) recommendation (Osman Elasha et al., 2006). The number of climate monitoring stations in Africa has also decreased since the 1970's (Hulme, 1992), which may result in less reliable observations and forecasts, especially in areas with strong environmental gradients such as the Sahel region (Sjöström et al., 2013). Estimates for Africa indicate, with high likelihood, higher future temperatures, warmer and more frequent hot days and nights or most land areas (IPCC, 2013b).

African precipitation shows a less clear pattern, both in terms of observations, as well as for predicted future precipitation patterns (Giannini et al., 2008; Boko et al., 2007). Interannual variability is large over most of Africa and some areas also show strong multi-decadal variability (Boko et al., 2007). During the last 50 years, declines in precipitation have been observed in West Africa, whereas a recent increase has been observed along the Guinean coast (Boko et al., 2007).

Some areas, such as southern Africa show no clear trend but some areas have experienced extreme precipitation events causing severe flooding (Usman and Reason, 2004). The recent greening observed in the Sahel (Olsson et al., 2005;

Dardel et al., 2014) is mainly explained by increased precipitation (Hickler et al., 2005). Predictions for the 21st century state that the Sahara region which is already very dry is very likely to remain very dry. The confidence in projection statements about drying or wetting of western Africa is low (IPCC, 2013b). A minor positive change in precipitation, with medium confidence is predicted for East Africa and changes in precipitation seasonality may occur in several regions.

The importance of sea surface temperatures and the monsoon are highlighted for the Sahel region whereas ENSO (El Niño–Southern Oscillation) may play an important role in southern Africa (IPCC, 2013b).

Effects of climate change Direct effects of increased temperatures include higher levels of plant and water stress, larger evaporative losses of water from soil and surface waters. This will decrease water availability for agriculture and water power and may further limit access to drinking water. Higher air temperatures increase the amount of water and energy that the atmosphere can hold which in turn may increase severity of extreme events (Field et al., 2012). Extreme precipitation events increase the risk of flooding and severe erosion causing damage to cultivation and infrastructure.

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