Editing IPCC:AR6/WGI/Chapter-8 (section)

==== 8.6.2.3 Amplification of Drought by Dust ====

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Mineral dust aerosols in the climate system originate from both semi-permanent and transient sources ( [[#Prospero--2002|Prospero et al., 2002]] ; [[#Ginoux--2012|Ginoux et al., 2012]] ). The former are typically arid regions where significant alluvial sediments have accumulated over time, while the latter are often associated with natural (e.g., droughts, wildfires) and anthropogenic (e.g., land use change, desertification) disturbances. Modern-day dust emissions are dominated by natural sources ( [[#Ginoux--2012|Ginoux et al., 2012]] ), although human emissions may contribute 10–60% of the global atmospheric dust load ( [[#Webb--2018|Webb and Pierre, 2018]] ). Paleo-dust records suggest that human factors (land use change and landscape disturbance) may have doubled global dust emissions between 1750 and the last quarter of the 20th century (Section 2.2.6; [[#Hooper--2018|Hooper and Marx, 2018]] ).

Dust aerosols influence the climate system and hydrologic cycle through both direct impacts on radiation (absorbing and scattering longwave and shortwave) and via indirect effects on cloud and precipitation processes (Box 8.1; [[#Choobari--2014|Choobari et al., 2014]] ; [[#Kok--2018|Kok et al., 2018]] ; [[#Schepanski--2018|Schepanski, 2018]] ). The capacity of dust aerosols to suppress precipitation by reducing humidity and energy availability, and increasing stability in the atmosphere ( [[#Cook--2013|Cook et al., 2013]] ; [[#Huang--2014|Huang et al., 2014]] ) can drive positive feedbacks (see also Section 6.3.6). Thus there is strong potential for dust to contribute to abrupt changes in the water cycle, especially in semi-arid regions where wind erosion is highly sensitive to vegetation cover and drought variability ( [[#Yu--2015|Yu et al., 2015]] ). One such event occurred over the Central USA during the 1930s: the Dust Bowl drought, an iconic event characterized by widespread land degradation and historically unprecedented levels of dust storm activity ( [[#Hansen--2004|Hansen and Libecap, 2004]] ; [[#Lee--2015|Lee and Gill, 2015]] ). While initialized by warm sea surface temperatures in the North Atlantic, modeling work indicates that land cover changes and resulting dust emissions contributed to the severity and spatial extent of the drought by further suppressing precipitation ( [[#Cook--2009|Cook et al., 2009]] ; [[#Hu--2018|Hu et al., 2018]] ; [[#Cowan--2020|Cowan et al., 2020]] ). There is also increasing evidence that dust aerosol feedbacks are necessary to explain the magnitude of rainfall increase during the mid-Holocene Green Sahara ( [[#Pausata--2016|Pausata et al., 2016]] ; [[#Tierney--2017|Tierney et al., 2017]] ).

The importance of dust aerosol feedbacks in future abrupt climate events, like droughts or rapid aridification, is unclear. In part, this is because the response of dust aerosol emissions and loading levels in the atmosphere to climate change is highly uncertain (Tegen and [[#Schepanski--2018|Schepanski, 2018]] ; [[#Webb--2018|Webb and Pierre, 2018]] ). This difficulty in predicting future dust responses is rooted in the fact that emissions depend on both changes to the land surface (e.g., land use/land cover change, aridification, ecological responses to climate change) and the state of the atmosphere (Tegen and [[#Schepanski--2018|Schepanski, 2018]] ). While there is some evidence that global dust aerosol concentrations in the future will increase ( [[#Allen--2016|Allen et al., 2016]] ; Tegen and [[#Schepanski--2018|Schepanski, 2018]] ), it is highly dependent on changes in precipitation patterns and atmospheric circulation (see the SRCCL, [[IPCC:Wg1:Chapter:Chapter-2#2.4.1|Section 2.4.1]] ), and it is not clear what the radiative impact will be ( [[#Allen--2016|Allen et al., 2016]] ; [[#Kok--2018|Kok et al., 2018]] ).

In summary, due to ''limited evidence'' , there is ''low confidence'' regarding the role of dust in abrupt climate change events over the next century.

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