Natural Dust in Atmosphere Has Doubled Since Start of 20th Century
The increase in dust in the Earth’s atmosphere is influencing climate and ecology around the world.
The amount of dust in the Earth’s atmosphere has doubled since the beginning of the 20th century and the dramatic increase is influencing climate and ecology around the world, according to a new study led by Natalie Mahowald, Cornell associate professor of earth and atmospheric sciences.
It’s the first study to trace the fluctuation of a natural (not human-caused) aerosol around the globe over the course of a century. Mahowald used available data and computer modeling to estimate the amount of desert dust or soil particles in the atmosphere, throughout the 20th century.
Desert dust and climate influence each other directly and indirectly through a host of intertwined systems. Dust limits the solar radiation that reaches the Earth, for example, a factor that could mask the warming effects of increasing atmospheric carbon dioxide. It also can influence clouds and precipitation, leading to droughts – which, in turn, leads to desertification and more dust.
Ocean chemistry is also intricately involved. Dust is a major source of iron, which is vital for plankton and other organisms that draw carbon out of the atmosphere.
To measure fluctuations in desert dust over the century, the researchers gathered existing data from ice cores, lake sediment and coral, each of which contain information about past concentrations of desert dust in the region.
They then linked each sample with its likely source region and calculated the rate of dust deposition over time. Applying components of a computer modeling system known as the Community Climate System Model, the researchers reconstructed the influence of desert dust on temperature, precipitation, ocean iron deposition, and terrestrial carbon uptake over time.
Among their results, the researchers found that regional changes in temperature and precipitation caused a global reduction in terrestrial carbon uptake of six parts per million (ppm) over the 20th century. The model also showed that dust deposited in oceans increased carbon uptake from the atmosphere by 6 percent, or four ppm, over that same time period.
While the majority of research related to aerosol effects on climate focuses on anthropogenic aerosols (those directly emitted by humans through combustion), Mahowald said, the study highlights the important role of natural aerosols as well. “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.