The Dusty Earth of the 21st Century

A new study says that over the past century, the amount of dust covering our planet has doubled, and this extreme increase is leaving its mark on the climate and ecology worldwide.

Natalie Mahowald, associate professor of earth and atmospheric sciences at Cornell University, and leader of the study, used all available computer modeling and data to make estimations of the amount of desert dust, or soil particles in the atmosphere, throughout the 20th century.

Most research focusing on aerosol impacts on climate includes only anthropogenic aerosols (those directly emitted by humans through combustion, but the researcher said that natural aerosols have their importance as well.

This is actually the first study to analyzed the variation of natural (not human-caused) aerosols around the globe over the course of a century.

It sounds a bit ironic but to measure the variations in desert dust over the past 100 years, the researchers took samples from ice cores, lake sediment and coral.

Every sample was then linked to its source region and allowed them to calculate the rate of dust deposition over time.

Then, thanks to the Community Climate System Model, the team recreated the influence of desert dust on temperature, ocean iron deposition, precipitation and terrestrial carbon uptake over time.

The results showed, among other things, that the regional changes in temperature and precipitation, triggered a global reduction in terrestrial carbon uptake of 6 parts per million (ppm) over the 20th century.

Also, over the same time period, the dust deposited in oceans increased carbon uptake from the atmosphere by 6% – or 4 ppm.

So the connection between desert dust and climate is quite strong, as they influence each other directly and indirectly through a host of interlaced systems – dust limits the solar radiation that reaches the Earth's surface, and this could actually mask the warming effects of increasing atmospheric CO2.

It's like a vicious circle, since this also influences clouds and rain, leading to droughts, which, in turn, lead to desertification and even more dust.

Mahowald said that “now we finally have some information on how the desert dust is fluctuating.

“This has a really big impact for the understanding of climate sensitivity,” she said, adding that it is very important to continue gathering more data and to refine the estimates.

“Some of what we're doing with this study is highlighting the best available data,” she explained, but “we really need to look at this more carefully; and we really need more paleodata records.”

The research was presented by Mahowald, at the fall meeting of the American Geophysical Union in San Francisco.