Variability of the Inter-Tropical Convergence Zone Related to Changes in Inter-Hemispheric Dust Load

Dust is a key forcing agent in climate and has major societal impacts on health, agriculture, and transportation. Dust varies on inter-annual to millennial timescales up to a factor of 20 between glacial and interglacial periods. Over the 20^th century, desert dust has doubled over much of the globe. In addition, dust has strong spatial heterogeneity producing disparate radiative forcing. Hemispheric asymmetry in dust concentrations has been observed between ice cores in Greenland and Antarctica and more recently between Australia and Africa in the 1970’s. Our objective is to assess the impact of such hemispheric dust asymmetry on climate with an emphasis on the Inter-Tropical Convergence Zone (ITCZ). We perform a set of experiments with the GFDL coupled climate models (CM3), modifying dust emission in each hemisphere by 0, 1, 2, and 5 times preindustrial levels. Dust load follows the imposed emission, which reduces the net radiative flux at the surface and top of the atmosphere. When dust load is asymmetric, we find that the radiative forcing is similarly asymmetric, generating an inter-hemispheric transfer of energy through the atmosphere and ocean and an associated shift in precipitation along the ITCZ. We find a linear relationship between radiative forcing and tropical precipitation asymmetry in the Atlantic. Our results show that dust plays a significant role in determining the latitudinal position of the ITCZ. Understanding this relationship is crucial for accurately predicting dust feedbacks and the effects of dust on future climate. This relationship is also important for understanding past climate variability such as the mid-Holocene and Last Glacial Maximum.