Evolution of Dust and Its Climatic Impact during Earth’s History

Dust, as one of the most common types of atmospheric aerosol, affects climate in many different ways. Atmospheric dust scatters and absorbs sunlight and reduces solar radiation received at the surface; it absorbs and emits longwave radiation, having a greenhouse effect; it has a complex indirect effect on climate by serving as cloud nuclei; when deposited on snow or ice, it reduces the surface albedo and warms the surface. Despite its importance in the climate system, how the dust emission and atmospheric dust loading varied during the Earth history is unclear. Here I will give a summary of the atmospheric dust loading as well as its climatic impact for a few typical periods of the Earth. All the results are from numerical simulations and are still premature due to uncertainties in vegetation cover and soil erodibility, and biases and inability of the climate model used.

In present day, the atmospheric dust loading is slightly more than 20 Tg, and has a small impact on the global climate. Such dust loading was diminished during the mid-Holocene (~6 thousand years ago; 6 ka) and the reduced dust induced a very slight global warming (~0.1 °C) but a cooling of the Northern Hemisphere by weakening the Atlantic meridional ocean circulation (AMOC). During the cold last glacial maximum (~21 ka), the atmospheric dust loading was ~2-3 times that of present day. Had not been this dust, the LGM climate would have been colder by ~2 °C and AMOC weaker by ~30%. Clearly, the snow-darkening effect of dust was dominative during this cold time period. For earlier periods with different continental configurations, the atmospheric dust loading also varied significantly. For 80 million years ago (Ma), the continents were dispersive and the total area of the continents was small, the atmospheric dust loading was only ~1.4 Tg. For 240 Ma, the continents clustered into a supercontinent and centered around the equator, the atmospheric dust loading ~21 Tg. For a continental configuration (130 Ma) that had an area in between 80 Ma and 240 Ma, the atmospheric dust loading was ~6.1 Tg. The dust had a cooling effect of <1 °C in all these three periods. For time periods earlier than 400 Ma when land vegetation had not evolved yet, the atmospheric dust loading could have been ~10 times of present day and cooled the climate by ~10 °C. However, such cooling effect disappeared and became a warming effect when the climate was entering a snowball Earth state, due to stronger and stronger snow-darkening effect.

Overall, there was more dust during a cold time period due to stronger winds, weaker hydrological cycle and more dust sources, and the dust had a warming effect to the climate. During the warm time periods, dust tended to have a cooling effect because there was too little snow and ice for the snow darkening by dust to be effective. There was also more dust during periods when the area of continents was larger and more clustered, due to drier land surface.