The presence of haze or African dust in the atmosphere is not something exclusive to Spain. Every year, Millions of tons of dust from the Sahara desert are swirled into the atmosphere by the easterly trade winds and carried across the Atlantic, ending up in places like the Amazon., where they fertilize plant life. A study now reveals that climate change will end up weakening this transport of dust in suspension.
In June 2020, a gigantic plume of dust traveled from the Sahara across the Atlantic Ocean to reach North America. While this conspicuous plume grabbed all the headlines, NASA scientists, using a combination of satellite data and computer models, predict that these masses of African haze will shrink more over the next century than they have in the past 20,000 years, as a result of the climate change and warming oceans.
The Sahara Desert is 9.2 million square kilometers of arid land that stretches across the northern half of Africa, and is slightly smaller in size than the United States. More of 60 million tons of its mineral powder laden with nutrients rise into the atmosphere each year, creating a massive layer of hot, dusty air that winds carry across the Atlantic to deliver those nutrients to the ocean and vegetation in South America and the Caribbean.
Recent NASA research describes the domino effect that occurs among desert elements to develop these dust plumes. The process begins with differences in temperature between the North and South Atlantic, and then the winds intervene constant east-west winds blowing in this region, as well as a relatively high tropical rain band located near the equator.
In this video you can see how the dust travels over the Atlantic.
The Sahara was never so dry before
“From ground-based and satellite observations, we see the variability of African dust,” said Tianle Yuan, an atmospheric scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
The peak of Saharan dust transport to the eastern side of the Americas occurred approximately 12,000 to 17,000 years ago, at the end of the last Ice Age. Then began the African Humid Period, during which the vast expanse of the desert was dotted with lakes, vegetation and human settlements. The increased humidity and plant life stabilized the soil and minimized dust plumes.
“The Sahara desert was relatively wet back then,” Yuan said. Offshore North African sediment cores and pollen records show that there was more rainfall and vegetation present. “The dust was much rarer,” she summarized.
Although dust transport has increased since then, the research team found that both natural processes and human activity are now driving Earth back to a dust minimum, as the climate warms.
30% less dust in suspension in this century
With global warming predicted, the research team used data from the Coupled Model Intercomparison Project 5 (CMIP5) model that indicate at least a 30% reduction in dust activity in the Sahara from current levels over the next 20 to 50 years, and a continuing decline thereafter.
“That minimum that humans experienced during the African Humid Period will probably now be exceeded, due to climate change,” Yuan said, referring to dust levels during the African Humid Period.
Sea surface temperatures directly influence wind speeds, so when the North Atlantic warms relative to the South Atlantic, the trade winds that blow dust from east to west weaken. As a result, those slower winds pick up and carry less dust from the Sahara.
In addition to carrying less dust, the weakening winds also allow the constant rain band that crosses the tropics to move north, dumping water over a larger part of the desert, moistening the dust and preventing it from being blown away.
Less dust in the air, which can reflect sunlight away from Earth’s surface like a sunshade, means more sunlight and heat reach the ocean, warming it even more. All of this creates a feedback loop of warm sea surface temperatures that leads to a reduction in dust. And that, in turn, contributes to additional warming, combining to influence climate, air quality, and the formation of storms and hurricanes.
Dust that fertilizes the Amazon
“Dust plays an important role in the Earth system,” said Hongbin Yu, an atmospheric researcher at Goddard. “A decrease in dust as the climate warms can have profound influences on a variety of phenomena, but these potential impacts can be good or bad.”
On its journey across the Atlantic, Saharan dust spreads into the ocean, feeding marine life and similarly plant life once it makes landfall. Minerals, such as iron and phosphorus in the dust, act as fertilizer for the Amazon rainforest, the largest and most biodiverse rainforest on Earth. Rains wash many of these valuable nutrients from the soil into the Amazon River basin, making nutrient delivery from Africa important for maintaining healthy vegetation.
Although African dust transport plays an important role in the genesis of soils and the sustenance of vegetation, Yu says that there are some negative effectsbecause increased nutrients can lead to harmful algae blooms off the Florida coast and dust-related coral reef disease.
Residents in the Caribbean could also see some benefits, as less dust means better air quality.. Breathing dust is particularly dangerous for childrenthe elderly and people with respiratory conditions such as asthma.
In fact, this threat led a team from NASA’s Earth Applied Sciences Program to develop an early warning system for Puerto Rico that now provides a three-day window of time before a Saharan dust storm hits Earth. the island, giving doctors and public health officials time to prepare and work with meteorologists on air quality alerts.
Reference article: https://phys.org/news/2021-04-nasa-saharan-future.html