Global warming will make Earth’s atmosphere dustier

The amount of dust in the atmosphere is limited by the presence of a “biocrust” composed of various micro-organisms, which preserve arid soils from wind erosion. This biocrust is however threatened by global warming and human activity. Its disappearance could lead to a significant increase in the amount of dust in the atmosphere by 2070.

Some 12% of the earth’s surface is covered by “biocrust”, or crust terrestrial biotic, which is a real living layer marking the surface part of the soil, most often in arid regions. This crust is generally composed of lichensof mosses and various cyanobacteria. She actively participates in ecosystems of these particular environments, in which it plays a central role, in particular for carbon and nitrogen fixationbut also for soil stabilization.

This last point is particularly important since the presence of a biotic crust prevents arid soils from being intensively eroded by winds and dust particles from ending up in theatmosphere. While this effect is recognized, there is however very little information to quantify and assess the real impact of the biocrust on the dust cycle in the atmosphere and therefore on the climate.

The presence of dust in the atmosphere impacts the climate

atmospheric dust is indeed one of the aerosols whose role in the climate system no longer needs to be proven. Most dust particles in the atmosphere are generated by wind erosion of soils in arid regions. These small grains can thus travel great distances, depending on the atmospheric currents. Their presence at altitude is however not insignificant, since it modifies the optical properties of the atmosphere by dispersing the solar radiation descending towards the ground and by absorbing certain wavelengths emitted from the ground. These particles also play a role in the formation of clouds.

If, on the one hand, dust transport has a positive role on productivity by providing nutrients in certain environments, on the other hand it can be harmful for human health but also for certain ecosystems. The climatic and environmental impact of atmospheric dust is complex and far from negligible. The question now is to know to what extent biocrusts make it possible to regulate this impact and to what extent their role may be affected by ongoing climate change.

Less biocrust, more dust in the atmosphere

A team of researchers therefore looked into these questions. Their results, published in Nature Geoscienceshow that biocrusts actually prevent theemission in the atmosphere of 700,000 tons of dust per year. Overall, the presence of these living layers in arid zones makes it possible to reduce the quantity of dust in the atmosphere by 60% compared to the hypothetical case where the biocrust would not exist.

The problem is that the biocrust is currently threatened by global warming, but also by the intense exploitation of the soil. Scientists estimate that by 2070, the surface covered with biocrusts will have drastically decreased by 25 to 40%. The loss of this protective layer could lead to an increase in wind erosion of the soil and therefore an increase of nearly 15% in the quantity of dust suspended in the atmosphere. The effect on climate could be significant, with a marked reduction in the overall radiation budget reaching the Earth’s surface.

This change in the level of atmospheric dust, for which it is still difficult to clearly estimate the climatic consequences, could however have a strong impact on the formation of clouds and therefore on the precipitation. The accumulation of dust on the glaciers and the caps could further accelerate their melting. Finally, the impact on human health and on the various biogeochemical cycles appears to be most certainly negative. This study shows that the evolution of biocrusts is an important factor to take into account in future modeling climatic.