Whether Sahara, Gobi or Namib: The dust of the earth’s deserts has a greater influence on the climate than previously assumed. Because the veil of dust in the atmosphere compensates for around eight percent of the anthropogenic warming caused by greenhouse gases, as new analyzes suggest. In addition, the amount of desert dust in the atmosphere has increased by around 55 percent since pre-industrial times – this also contributes to the cooling buffer effect. However, should dust levels drop again, this could increase warming.
Volcanic eruptions, forest fires, exhaust fumes and the desert dust thrown up by the wind have an effect on the climate: Depending on their size, brightness and location, such aerosols can promote or impede cloud formation, reflect sunlight as a bright veil or darken the surface of glaciers and snow areas. Such suspended particles therefore have a partly cooling and partly warming effect on the climate.
It is known, for example, that the sulfur aerosols released during volcanic eruptions, asteroid impacts or industrial emissions primarily have a cooling effect. This is one of the reasons why it is being discussed whether this could be used in the context of geoengineering.
But what about the climate effect of desert dust? This dust enters the atmosphere when dust particles are kicked up from the desert floor. With the wind and prevailing air currents, they can then be transported over enormous distances – for example from the Sahara across the Atlantic. Millions of tons of dust enter the earth’s atmosphere every year.
The desert dust makes up a large part of all aerosols present in the earth’s atmosphere. The Sahara and the Gobi desert in Asia alone are responsible for 50 percent of the earth’s aerosol budget, as Jasper Kok from the University of California in Los Angeles and his colleagues explain. In a review article, you have now examined in more detail how the desert dust load has changed over time and what effect it has on the climate.
The analysis of bog samples and ice and sediment cores showed that since the pre-industrial period around 1850, the amount of desert dust in the earth’s atmosphere has increased from 19 million to 29 million tons. This corresponds to an increase of 55 percent. “Dust from Asia, which has even increased by 74 percent, accounts for the largest share,” report Kok and his team. It is followed by dust from the North African Sahara with 46 percent.
The researchers see changes in land use as the primary cause of these increased dust emissions, especially on the outskirts of the large desert areas. As agriculture increases, tillage contributes to erosion and dust raising, the team explains. But increasing drying out of soil and lakes due to climate change also plays a role. Globally, however, dust emissions appear to have largely stabilized since 2000, as satellite data suggest.
But how big is the climate impact of this desert dust? According to calculations by Kok and his team, the dust thrown up has a mostly net cooling effect. Overall, it reduces the earth’s radiative output – the energy from the sun’s rays – by 0.2 watts per square meter. This corresponds to around eight percent of the warming caused by anthropogenic greenhouse gases. The increase in desert dust since 1850 accounts for around 0.07 watts per square meter.
Measured against the total global warming, this cooling effect is not very large – but large enough to be taken into account in climate models. Because only then are precise predictions and modeling possible. So far, however, this dust load has only been partially recorded, as the research team explains. “The historical increase in the dust load is even completely missing in the current climate models,” say Kok and his colleagues. This needs to be improved.
For the climate, the dusty cooling effect also means that the coming warming also depends, at least in part, on the Earth’s deserts and soil erosion. If dust emissions no longer increase or even drop significantly, this could further intensify global warming. (Nature Reviews Earth Environment, 2023; doi: 10.1038/s43017-022-00379-5)
Source: Nature Reviews, Research Center Jülich
This article was written by Nadja Podbregar
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The original of this post “What desert dust can counteract climate change” comes from scinexx.