Proceedings of the 4th World Conference on Climate Change and Global Warming
Year: 2024
DOI:
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Potential Global Sequestration of Atmospheric Carbon Dioxide by Drylands Forestation
Murray Moinester, Rafat Qubaja, Joel Kronfeld
ABSTRACT:
The CO2 sequestration potential of global drylands forestation is estimated. Drylands (31 million km2, hot arid and hot semiarid) comprise a significant fraction of the global land surface. The organic and inorganic carbon sequestration rates at Israel’s planted Yatir forest were measured. This forest sequesters ~550 g CO2 m-2 yr-1 (150 g C) organic carbon in the tree’s biomass, and ~132 g CO2 m-2 yr-1 (36 g C) inorganic carbon (arising from root exhalation of CO2) primarily as calcite (CaCO3) in the top (~6 m) of the soil’s unsaturated zone. In addition, calcite precipitation takes place when soil microbes in the uppermost meter of soils interact with diffused atmospheric CO2. The Yair Forest is taken here as representative of typical global dryland forests. It is a 28 km2 Aleppo pine forest growing at the semi-arid timberline (with no irrigation or fertilization). The potential maximal efficacy of global afforestation depends on the maximal area available for sustainable forestation. The dominant limitation, particularly in the vast desert regions, is the apparent lack of water. This would reduce the potential area for sustainable forestation to a published estimate of roughly 4.5 million km2. Assuming forestation of this area, we estimate the maximal total global drylands sequestration rate to be ~3.5 billion tons CO2 yr−1; divided between 2.5 and 1.0 billion tons organic and inorganic, respectively. However, this estimate does not take into account an important hydrogeologic fact; namely, that in many drylands areas, plentiful water is available from immediately underlying local paleowater (fossil) aquifers. Using these areas, so far not considered, would increase the functional dryland forestation area to at least 9.0 million km2; thereby increasing the potential total sequestration rate to a minimum of ~7.0 Gt CO2 yr−1. However, the transformation of bright high albedo desert areas to dark forests would reduce the positive climate cooling effects. For a 7.0 Gt yr−1 total rate, based on published estimates, the total CO2 “equivalent” atmospheric cooling sequestration rate would be reduced to 5.0 Gt yr−1. The actual effective reduction may be less, considering that drylands forestation would decrease surface temperature through the increase of evapotranspiration; and because the increased evaporation (thanks to irrigation) would increase albedo due to increased low elevation cloud cover. The global climate effects of increased evaporation and the albedo effect due to drylands forestation require further study. Estimating more precise effective sequestration values would also require taking into account the choice of tree species, stand densities, canopy cover, precipitation levels, cloud cover, and also how CO2 concentrations equilibrate between atmosphere, land and oceans. Still, our first estimate already demonstrates a significant potential for reducing global warming. Besides, dryland forests would provide important ancillary environmental benefits. These include preventing encroaching desertification, producing oxygen, increasing precipitation and evaporation and cloud cover, reducing ocean acidification, improving soil structure and quality and soil stability, reducing erosion and runoff, reducing soil biogenic nitric oxide emissions, reducing air particulate pollution, providing lumber and charcoal, providing wildlife habitat and recreational facilities, providing forest management employment to local populations; and producing carbon offset credits to be sold on global carbon trade exchanges to help support forestation activities. Although further measurements are called for, there is already justification to begin implementing a global land management policy of widespread tree planting in drylands.
keywords: global carbon sequestration; organic and inorganic carbon; drylands forestation