Desertification and Climate Change
Desertification is the ongoing process of dry ecosystem degradation due to human mismanagement, a process which started with the beginning of human civilization and continues to this day. Desertification has created huge expanses of infertile, desert-like terrain that was previously productive farmland, savannas or woodlands. Desertification and global warming are intricately connected. Rising temperatures and changing precipitation patterns are expected to increase the rates of dryland degradation and desertification, and major river systems in drylands are predicted to gradually dry out. Manmade desertification and ecosystem degradation have, over the course of the millennia, emitted more carbon dioxide into the atmosphere than has been emitted so far by the burning of fossil fuels. Another impact of desertification with respect to global warming is the fact that degraded, de-vegetated ecosystems are much less resilient to the increasing frequency of climate extremes such as drought, heatwaves and floods. In light of these facts, the huge environmental and economic potential of ecosystem restoration, especially in degraded dryland environments, becomes acutely evident. Global dryland restoration could sequester hundreds of gigatons of carbon dioxide back into biomass and soil, while restoring sustainable, productive potential for food, fodder, energy and biomaterials. Similarly, diverse natural ecosystems and plant and animal biodiversity can be restored to vast areas of degraded deserts. Project Wadi Attir is a small, but fully integrated and holistic effort to demonstrate and quantify those complex interactions while providing significant economic and social gains.
Global warming or global climate change is the observed rise in global average temperatures and associated phenomena such as shrinking polar and mountain glaciers, shifting vegetation zones, rising ocean temperatures and rising sea levels. Global warming is caused by exponential growth of greenhouse gas concentrations (carbon dioxide, methane, nitric oxides and others) in the atmosphere, due to fossil fuel combustion, deforestation, soil degradation, industrial activities, agrochemicals and a growing number of ruminants. Increasing atmospheric greenhouse gas concentrations reduce the amount of heat radiation escaping to space and thus lead to a gradual, but significant increase in global temperatures. The ‘Intergovernmental Panel on Climate Change’ (IPCC) is continuously assessing the science underlying global warming and the potential risks and impacts of rising temperatures. These findings are periodically summarized and published in so-called ‘Assessment Reports.’ To date, average global temperatures have increased by almost one degree centigrade over pre-industrial times (Fig. 2) causing noticeable changes such as sea level rise, rapidly retreating ice cover in the Arctic, rapidly changing vegetation in subarctic zones, melting permafrost, and more.
Fig. 1: Global warming and desertification are mutually interacting environmental calamities. Average global temperatures have risen to almost 1oC above the 19th century average, and the warming trend is expected to accelerate in accordance with exponentially rising concentrations of greenhouse gases in the atmosphere and dangerous positive feedback mechanisms. Mismanagement continues to cause degradation of large dryland areas, such as in this location near Project Wadi Attir (right). Restoring vegetation and soil organic matter in such degraded areas can sequester significant amounts of the greenhouse gas carbon dioxide, while increasing agricultural productivity and ecosystem resilience.
Fig. 2: Global average temperatures have been rising steadily in the course of the industrial age, in accordance with rising concentrations of atmospheric carbon dioxide and other greenhouse gases. The black line indicates the 1oC difference between the late 19th century average and 2014’s record global temperature average.
Further warming is expected to result in serious environmental impacts all around the world. Changes in rainfall patterns may disrupt agricultural production and river flows, threatening the existence of major population concentrations. Disruptions in global supply chains may result in serious security threats, together with decreasing food and water security. Two parallel strategies are being recommended to cope with global warming: 1. Mitigation, meaning avoiding the release of further greenhouse gasses or facilitating their sequestration back into biomass, or 2. Adaptation to the effects of climate change by enhancing the resilience of ecosystems, agriculture, infrastructure, the economy, settlements and societies as a whole, in order to better cope with a changing climate and its expected impacts. Fighting land degradation by restoring soils and vegetation is an equally suitable response to both objectives and consequently deserves urgent consideration.
Fig. 3: The ice cover of the Arctic is decreasing much faster than predicted and modeled, creating a dangerous positive feedback mechanism to further accelerate global warming, by decreasing the amount of reflected light and increasing methane emissions from thawing permafrost. Such positive feedback mechanisms can amplify and potentiate the dangers of global warming. Their consequences are difficult to model.
Desertification is one of the dominant present-day environmental calamities, affecting hundreds of millions of dryland inhabitants and an unspecified area, estimated between 1000 – 3000 million hectares (Dregne and Chou, 1992; Safriel and Adeel, 2005). Early civilizations have caused significant and often irreversible land degradation in arid, semiarid and sub-humid areas in the Middle East and the Mediterranean Basin, South and Central Asia and Central America (Fig. 4, Ruddimann, 2003; Fig. 5). In most semi-arid and sub-humid areas of Africa and Asia, but also in Israel, desertification is still progressing unchecked due to intensive farming, deforestation, overgrazing and inadequate irrigation and farming technologies. The United Nations Convention for Combatting Desertification (UNCDD) coordinates the efforts against desertification globally and has adopted a near-term goal of zero net land degradation.
Fig. 4: A classical example of desertification from ancient times. Parts of the Judean Mountains have seen extreme degradation and complete soil loss to the extent that large slabs of bare rock are now exposed. This phenomenon is observed extensively all around the Mediterranean coast, and was already described in detail 2,500 years ago in Plato’s ‘Critias.’
Interrelation Between Global Warming and Desertification
Recent research and reviews have outlined the tight interrelation between global warming and land degradation. Desertification not only causes loss of productivity with serious impacts on food production, future food security and economic development (Safriel and Adeel, 2005; Hussein, 2008), but also causes the release of greenhouse gases to the atmosphere, thereby accelerating global warming. Decomposition of soil organic matter and biomass during the last 7,800 years caused by land degradation and desertification has resulted in carbon dioxide emissions estimated at 450 – 500 gigatons of carbon (Ruddimann, 2003, Fig. 5; Lal, 2004), which corresponds to more than the total amount of CO2 emitted from fossil fuel combustion so far.
Fig. 5: The large-scale impact of historical land degradation has been modeled and analyzed by Ruddiman (2003). The black and grey areas have been profoundly degraded and in part transformed to deserts, a process that already took place more than 2,000 years ago.
More recently, rapid deforestation—mainly the destruction of rainforests—and large-scale degradation of dryland soils and vegetation have continued to comprise up to 20% of rising greenhouse gas concentrations in the atmosphere. Such degraded lands become more sensitive to increasing climate extremes such as heatwaves, droughts and flash floods. Vegetation loss and soil degradation also enhance ecosystem sensitivity to further erosion and desertification.
Integrated Ecosystem Rehabilitation
Large-scale restoration of degraded ecosystems can mitigate floods, droughts, erosion and other effects of weather extremes, and has been successfully applied in many countries (see GAIA – an Atlas of Planet Management). Furthermore, the large-scale rehabilitation of degraded ecosystems sequesters huge amounts of carbon dioxide into recovering biomass, and into newly formed soil organic matter. An integrated global biosphere rehabilitation program based on reforestation, desertification control and sustainable agriculture using agroforestry and permaculture-like farming systems, could sequester sufficient carbon dioxide into biomass and soils to temporarily stabilize atmospheric carbon dioxide concentrations (Fig. 6, Leu 1990).
Fig. 6: Hypothetical impact of a large-scale biosphere protection and restoration program on atmospheric carbon dioxide concentrations, as modeled in 1992. Decisive action addressing deforestation, desertification and more sustainable agriculture could provide a 50-year break in atmospheric greenhouse gas accumulation.
Lal (2001) predicted a yearly sink of 3 – 6 gigatons of CO2 by carbon sequestration into degraded dryland soils alone, a number which has been confirmed by several independent analyses. The global carbon sink potential of dryland rehabilitation is up to ten gigatons of carbon dioxide per year (Grunzweig et al, 2003; Leu, 2005). This corresponds to about 25% of anthropogenic greenhouse gas emissions, and up to 50% of the greenhouse gas accumulation rate in the atmosphere. Rehabilitation of degraded drylands would also restore essential ecosystem services such as biodiversity, sustainable wood supply, fodder, food, and renewable energy—essential commodities in a world more and more limited in land and water (Leu, 2005; Abu Rabbia et al. 2008, Leu 2010). Combatting desertification is therefore predicted to play a central role, both in mitigating global warming, and in adaptation to global warming. Together with expected positive economic and social impacts, dryland restoration emerges as a top-priority, win-win approach in sustainable development.
Carbon Emissions, Sequestration, and Rehabilitation
Fig. 7: The greenhouse gas balance of desertification or rehabilitation is relatively straightforward. Degradation leads to destruction and oxidation of biomass, and to the conversion of soil organic matter to carbon dioxide that is emitted to the atmosphere, thereby enhancing global warming. Restoring vegetation and soil by means of rehabilitation sequesters carbon dioxide from the atmosphere back into biomass and soil, in the form of plant litter, roots and soil organic matter. This can be a long-term process, whereby plant induced rock-withering, together with decomposing biomass, can slowly restore the original, fertile humus layers that were lost by erosion.
A recent analysis by Rotenberg and Yakir (2010) has cast doubt on the benefits of dryland afforestations since albedo changes associated with afforestations may temporarily surpass the gains achieved by carbon sequestration. Further controversies concerning dryland afforestation have to do with the claimed competition between trees and herbaceous vegetation for water and resources, and the depletion of groundwater and aquifers by trees. IPCC for example does not support dryland afforestation for carbon sequestration. Those arguments have been discredited to a large extent by recent research indicating that appropriate dryland afforestations do safeguard significant amounts of moisture while reducing erosion and water runoff. Therefore, the climatic impact of desertification control and dryland rehabilitation warrants a more detailed analysis (Leu, 2010) which takes into account all ecosystem services provided by intact dryland ecosystems such as biological production potentials for fodder, biomass or other agricultural products (Leu, 2005; Safriel and Adeel, 2005, Abu Rabia et al. 2008), watershed management and protection, erosion control, soil conservation, biodiversity and others. The following picture series summarizes the approximate carbon balance and services of three stages of dryland degradation (Fig. 7) determined in research undertaken while developing Project Wadi Attir.
Fig 7A. Shrubland area degraded by overgrazing and soil movement: SOM 2-3%; aboveground standing biomass 0 – 1 ton per hectare; soil nutrient content and water infiltration very low; very high water runoff; biological productivity 0.5 – 1 ton per hectare per year.
Fig. 7B. Conserved, moderately-grazed shrubland: SOM 3-5%; aboveground biomass 3 – 5 tons per hectare; soil nutrient content and water infiltration high in shrub patches, water runoff low; biological productivity 2 – 4 tons per hectare per year.
Fig. 7C: Acacia woodland (18 years old): SOM 5%; aboveground biomass, including litter: 20-25 tons per hectare; soil nutrient content and water infiltration high, zero water runoff; biological productivity 7-9 tons per hectare per year.
All pictures shown in Figure 7 were taken on the same date in an arid area 6 km north of Project Wadi Attir. Our recent assessment of the areas shown in Figure 7 indicates that a 20-year-old dry Acacia woodland stores over 100 tons per hectare more CO2 in topsoil and biomass than the degraded shrubland.
Solar Radiation Impact of Desertification
A major impact of desertification is a complete change in the way the land surface interacts with solar radiation, leading to a wide range of possible impacts on climate and global warming (see Rotenberg and Yakir 2010), as documented in an ensuing discussion in Science Magazine (Leu 2010 and related articles, see references in the ‘science and educational resources’ page). The schematic representation in Figure 8 tries to briefly summarize the major possible interactions and climatic effects caused by altering the radiation balance in a denuded, desertified landscape (A), compared to a replanted dryland forest (B).
Fig 8: Schematic representation of radiation interactions in desertified (A) and vegetated (B) drylands:
(A) – Desertified surfaces have high albedo and reflect some sunlight back to space (yellow arrows). The remaining radiation, however, is absorbed by the exposed soil and rock, leaving the air relatively cool and creating a high-pressure system, reducing the probability of precipitation. The heated surface releases energy in the form of longwave infrared radiation (blackbody radiation, brown to orange arrow), that interacts fully with the absorption bands of the major greenhouse gasses (CO2, methane, NOx and water), thus heating the atmosphere and contributing to global warming (symbolized by the brown-orange cloud).
(B) – Restored vegetated surfaces have low albedo and absorb all or most of the incoming sunlight. Some of it is immediately released from vegetation as chlorophyll fluorescence and other shortwave infrared radiation that escapes to space unhindered (red dotted arrow). The remaining light energy is converted into heat radiation in the forest canopy, and enhances the trees evapotranspiration, triggering rising of the hot and humid air masses (violet/blue arrow), while creating a low-pressure system. If the resulting uplift and humidity are sufficient, clouds form as soon as cooler air masses are encountered.
Yattir forest and nearby afforestations are the driest continuous forest systems in Israel. Though an initial warming effect is predicted due to reduced albedo, the forest also seems, based on empiric observations, to induce cloud formation, especially in early summer when high soil humidity permits significant evapotranspiration (Fig. 9). This phenomenon may become significant once larger vegetated areas are restored to their maximal water-use efficiency.
Fig 9: Yattir forest is a significant source for convective cloud induction, especially in late spring/early summer, when humidity available to the trees is still high, and temperatures and radiation intensity start rising. The precise climate impact of this and other climate-related effects of dryland restoration remain to be quantified (Leu 2010).
Soil Hydrology of Desertification and Rehabilitation
Desertification dramatically alters the hydrology of the degraded soil surfaces. Desertified surfaces are either rocky surfaces or exposed crusted soils with very low water infiltration capacity; water immediately runs off at high speed, causing further soil erosion. Remaining humidity in exposed soils rapidly evaporates in the intensive sunlight, so that resulting biological productivity is a fraction of that of restored ecosystems. In intact or restored ecosystems, large amounts of water can infiltrate through layers of plant litter into rich topsoil, whereby decomposing litter releases the nutrients required for vigorous plant growth (Fig. 10). Shade provided by perennial plants and plant litter layers also reduces soil surface temperatures and, consequently, evaporation, so that most precipitation becomes available to plants, resulting in superior water-use efficiency (Fig. 11).
Fig. 10: Mechanisms and impacts of dryland degradation and rehabilitation. Significant levels of rehabilitation and soil restoration can be achieved within 20 years, though gains in carbon sequestration, soil improvement, biological productivity and hydrology can continue growing for one hundred years or more.
Fig 11: Even moderate land degradation results in a dramatic reduction in water-use efficiency due to increased water runoff and evaporation. A large-scale analysis using NDVI to estimate biological productivity (Helmann et al 2014) demonstrated that conserved areas produce up to double the amount of biomass per unit of precipitation than degraded areas.
Dryland Rehabilitation by Silvipasture and Agroforestry
Agroforestry and silvipasture are effective methods of land rehabilitation, while creating significant carbon sinks and providing subsistence income to private landowners (Montagnini and Nair, 2004; Abu Rabia et al. 2008; Smith, 2009). They are thus win-win strategies for reversing environmental degradation, economic deterioration and climate change (Leu, 2005). Silvipasture is an effective tool for making livestock grazing more sustainable by contributing to the rehabilitation of degraded soils, the provision of tree products and the increase of fodder availability. Recent research in arid shrubland in Southern Israel indicates that silvipasture using A. victoria has a variety of benefits in terms of rangeland improvement, fodder production, soil rehabilitation and biodiversity.
Fig. 12: Heavily degraded contour-trenched afforestation, compared to a restored silvipasture savannah. Both approaches were initiated at the same time (and both pictures were taken on the same day).
Project Wadi Attir as a Showcase for Sustainable Dryland Development
Re-vegetation and soil rehabilitation are key low-tech technologies, applicable to huge degraded areas in the arid, semi-arid and sub-humid climate zones. Forestry has often been presented as a means for carbon sequestration only. However, the planting of adequate agroforestry species and the application of sustainable soil management approaches transform such woodlands into multipurpose agroforestry plantations for the production of food, fodder, energy and timber. Local production of such goods can significantly reduce transport distances and costs, while replacing high-impact farm products produced in intensive agriculture. Recent economic and life cycle assessments by Dr. Leu indicate that fodder and food production in restored dryland ecosystems are highly profitable, since formerly wasted, free resources such as water and land are put to productive use while biodiversity is being restored and greenhouse gases are being sequestered into soil and biomass (Fig. 12). This indicates that dryland rehabilitation is an excellent tool to overcome the apparent land-water-food crisis in a sustainable and profitable way, both locally and globally. These approaches are being put to use at Project Wadi Attir, where we have just reaped the benefits of the first harvests of olives and pomegranates, fodder and biomass production are increasing, and carbon sequestration by planted trees and restored soils are already setting in (Fig. 13).
Fig. 13: Agroforestry and silvipasture provide value far beyond carbon sequestration alone, and thus need to be implemented independently to enhance food security and the sustainability of the global food production chain. In the picture above, olive plantations stabilize an eroding dry valley. Below, an edible dry forest composed of Moringa and Prosopis stabilizes an agroforestry terrace.
Project Wadi Attir, together with other minor projects, is unique within 200,000 hectares of degraded drylands in the Northern Negev. Applied to this whole area, careful rehabilitation could sequester 10 – 20 million tons of carbon dioxide, while providing work and income to thousands. Enhanced fodder production would strongly reduce the greenhouse gas footprint of animal husbandry, because of reduced fodder import and transport needs. The economics of each restoration approach is different. Nevertheless, a general business model, as outlined in the scheme below (Fig. 14) and confirmed by assessments at Project Wadi Attir and nearby sustainable farming enterprises (Abu Rabia et al 2008), indicates that the investments required for restoration efforts can be recovered within a few years. The major obstacles to implementation are often the lack of land ownership and/or capital. Both issues should be addressed urgently, considering the huge potential for environmental and economic benefit.
Fig. 14: Expected outcome of a dryland restoration program involving agroforestry and silvipasture approaches, for the production of fruit, food, fuel and livestock fodder. The predicted timescales have been confirmed in nearby farming ventures, as well as during the first three years of project implementation at Project Wadi Attir.