Over the past few decades, numerous studies have been conducted on the exchange of greenhouse gases between the atmosphere and the biosphere. Of these gases, carbon dioxide (CO2) is the most studied, given its continuous increase in the atmosphere and its contribution to the increase in global temperature.
One third of CO2 emissions caused by human activities are absorbed by terrestrial ecosystems. Ecosystems such as forests, wetlands and jungles play a crucial role in this absorption. However, what often goes unnoticed is that deserts and tundras are also important in this process, although in a different way.
The role of arid regions in the carbon cycle
Arid regions, such as deserts, have traditionally been ignored in terms of their role in the carbon cycle. This is because, compared to other ecosystems, their biological activity is much lower. However, recent studies have shown that these ecosystems play a crucial role in the global carbon balance, and not only by absorbing CO2. Research led by the Consejo Superior de Investigaciones Científicas (CSIC) have revealed that the CO2 emissions in arid areas can be triggered by wind, through a process called 'underground ventilation'.
This phenomenon occurs when CO2-laden air trapped underground is expelled into the atmosphere due to atmospheric turbulence caused by wind. This process is particularly intense during the dry season in places with low soil moisture. CO2 emissions of this type in arid ecosystems have been widely underestimated, and current research indicates that they could contribute significantly to the increase in greenhouse gases.
The experimental site in Cabo de Gata
One of the most relevant studies on underground ventilation has been carried out in a semi-arid esparto grassland in the Cabo de Gata-Níjar Natural Park, Almería. This site was chosen due to its extreme aridity and low biological activity, making it an ideal reference point for measuring CO2 emissions in arid climates. For six years, between 2009 and 2015, researchers measured carbon dioxide levels in the soil and atmosphere.
The results indicated that under windier and drier conditions, significant emissions of CO2 are produced from the soil into the atmosphere, altering the carbon balance. In fact, it was observed that at certain times CO2 trapped underground is released in large quantities, forming an additional emissions stream.
The vulnerability of carbon stored in arid soils
According to recent studies, Organic carbon stored in arid soils is much more vulnerable than previously thought. Soil minerals were expected to act as protective shields to prevent the release of this carbon. However, research by the Institute of Agricultural Sciences (ICA) of the CSIC has revealed that the minerals present in these areas are not as effective as previously thought. As a result, the increase in aridity and temperatures due to climate change is causing unexpected carbon losses in these ecosystems.
These carbon losses have a double impact. On the one hand, they release more CO2 into the atmosphere, which contributes to global warmingOn the other hand, this loss also directly affects biodiversity and soil fertility in arid areas, since organic carbon is essential for these ecosystems.
The impact of climate change on arid zones
Climate change is severely affecting arid and semi-arid ecosystems. Projections of Increased droughts and expansion of arid zones could significantly increase the phenomenon of underground ventilation, which could transform these areas from being carbon sinks into net emitters of CO2.
A study by King Abdullah University of Science and Technology estimates that this situation could completely alter the global carbon balance. Unless measures are taken to mitigate the effects of climate change, arid ecosystems could accelerate the process of global warming, contributing significant amounts of additional CO2 to the atmosphere.
In addition, in these areas where the soil moisture is less than 30%, wind and lack of vegetation facilitate the escape of CO2 trapped underground. This suggests that climate projections for the coming decades could worsen the situation in arid areas, increasing CO2 emissions globally.
On the other hand, some studies suggest that arid areas could capture more CO2 than previously thought if they were 're-greened'. Plants adapted to arid environments, together with certain soil microorganisms, could be key to restoring carbon absorption capacities in these areas.
In summary, while drylands have been overlooked in carbon cycle studies, recent research highlights their relevance and great complexity. Rising CO2 emissions due to underground ventilation and the vulnerability of stored carbon make these regions a necessary focus of attention in the context of climate change.