Researchers propose critical role of desert dust in Earth’s climate system

Several types of cirrus clouds [image credit: Piccolo Namek @ Wikipedia]

Headline: ‘Airborne study reveals surprisingly large role of desert dust in forming cirrus clouds’. Researchers found ‘Even at low concentrations dust was found to play a big role in controlling cloud properties’. One said: “These results are a striking message to the aerosol and cloud science community, that we need to improve our treatment of dust and cloud formation in climate models to more accurately predict current and future climate.” Not much faith can be put in predictions of the future climate if predicting the present one is known to be inaccurate?
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Every year several billion metric tons of mineral dust are lofted into the atmosphere from the world’s arid regions, making dust one of the most abundant types of aerosol particles in the atmosphere, says Phys.org.

Now, scientists are learning that tiny bits of dust from the hottest and driest parts of the Earth are a surprisingly large driver in forming the delicate, wispy ice clouds known as cirrus in the cold, high-altitudes of the atmosphere.

While scientists have known that desert dust particles can seed certain clouds, the extent of that relationship has been a long-standing question.

New research, based on the largest-ever airborne atmospheric sampling mission and published in Nature Geoscience, sheds light on the role of dust in the climate system.

“Dust-initiated cirrus clouds are surprisingly abundant, accounting for 34 to 71% of all cirrus clouds outside of the tropics,” explained lead author Karl Froyd, a CIRES scientist at NOAA’s Chemical Sciences Laboratory with the Aerosol Properties & Processes research program at the time of the study. “Perhaps even more surprising, we found that although the Sahara Desert is by far the world’s largest dust emitter, the deserts in Central Asia are often more important sources for cirrus formation.”

Analysis of atmospheric measurements collected over the remote oceans during NASA’s three-year Atmospheric Tomography Mission (ATom) reveals that dust plays a dominant role in forming cirrus clouds across both the northern and southern hemispheres, and that certain deserts are far more efficient than others when it comes to cloud creation.

To explore the role of wind-blown dust in creating cirrus clouds, Froyd and colleagues deployed a custom-built, single-particle mass spectrometer, known as PALMS, on the NASA DC-8 research aircraft during the ATom project to measure the chemical composition of aerosol particles in the remote atmosphere.

ATom flights circumnavigated the globe four times between 2016–2018, flying long transects down the Pacific and Atlantic Oceans and across the Arctic and Southern Oceans.

While flying, the PALMS instrument continuously ingested atmospheric particles, one by one, using a laser to vaporize each into their individual components before they’re sent into a mass spectrometer to reveal their chemical signatures. Mineral dust is just one of the many aerosol types that this powerful instrument is able to identify.

Researchers encountered continental dust across nearly every altitude and latitude sampled by the aircraft, including over the Southern Ocean, the remote Pacific, and Antarctica. The levels of dust present in the cirrus-forming upper troposphere were quite low, far below what could be observed by a satellite, but were ubiquitous.

Even at low concentrations dust was found to play a big role in controlling cloud properties.

The extensive dust measurements collected during ATom were incorporated into a detailed atmospheric model capable of simulating cirrus formation to quantify the effects of dust on cirrus across the globe.

Despite the minute quantities of dust aerosols measured in the upper troposphere, dust is still abundant enough to drive cirrus cloud formation during all seasons throughout the extra-tropics, including the Southern Hemisphere.

Full article here.
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Research article: Dominant role of mineral dust in cirrus cloud formation revealed by global-scale measurements (Nature Geoscience)