UCLA researchers have found that global atmospheric dust has masked the full potential of greenhouse gases’ role in climate change.
A study led by UCLA researchers has revealed that global atmospheric dust – microscopic airborne particles from desert dust storms – has a slight overall cooling effect on the planet. This phenomenon is thought to have masked the full amount of warming caused by greenhouse gases. Because of this, if dust levels stop climbing, there is potential for climate change to slightly increase in speed.
The research, ‘Mineral dust aerosol impacts on global climate and climate change,’ published in the journal Nature Reviews Earth and Environment, found that the amount of desert dust has grown roughly 55% since the mid-1800s, which increased the dust’s cooling effect.
The study is the first to demonstrate the overall cooling effect of atmospheric desert dust
The planet can be warmed by some effects of atmospheric dust, but because other effects of dust counteract warming, such as by scattering sunlight back into space and dissipating high clouds that warm the planet, the researchers concluded that dust’s overall effect is a cooling one.
If dust levels decline or simply stop growing, climate change could ramp up, explained UCLA atmospheric physicist Jasper Kok, the study’s lead author.
“We show desert dust has increased, and most likely slightly counteracted greenhouse warming, which is missing from current climate models,” said Kok, who studies how particulate matter affects the climate.
“The increased dust hasn’t caused a whole lot of cooling — the climate models are still close — but our findings imply that greenhouses gases alone could cause even more climate warming than models currently predict,” he said.
The researchers compared the discovery to finding out that a vehicle’s emergency brake has been partly engaged while driving at high speed. Similar to releasing the brake, which could cause the car to move even faster, a stop to the increase in dust levels could slightly speed up climate change.
Although atmospheric desert dust levels have increased overall since pre-industrial times, the trend has not been steady as there are many natural and human-influenced variables that can cause dust levels to increase or decrease. Because of this, scientists cannot accurately project how the amounts of atmospheric dust will change in the coming decades
How does desert dust mask the effects of climate change?
Some of the microscopic airborne particles created by burning fossil fuels also temporarily contribute to cooling, Kok said. But although scientists have spent several years determining the consequences of human-made aerosols, the precise warming or cooling effect of desert dust remained unclear until now.
As well as interacting with sunlight and cloud cover, dust can darken snow and ice when it drops back to Earth, making them absorb more heat. Dust also deposits nutrients like iron and phosphorous, which when taken in by the ocean, support the growth of phytoplankton that take up carbon dioxide from the atmosphere. This, therefore, causes a net cooling effect.
Human actions have warmed the planet by 1.2°C since around 1850, and without the increase in dust, climate change would likely have already warmed the planet by a greater degree. As the planet is close to the 1.5°C of warming that scientists consider dangerous, every tenth of a degree matters, Kok said.
“We want climate projections to be as accurate as possible, and this dust increase could have masked up to 8% of the greenhouse warming,” Kok said. “By adding the increase in desert dust, which accounts for over half of the atmosphere’s mass of particulate matter, we can increase the accuracy of climate model predictions. This is of tremendous importance because better predictions can inform better decisions of how to mitigate or adapt to climate change.”
It is unknown whether desert dust levels will change
The team used satellite and ground measurements to quantify the current amount of microscopic mineral particles in the air and found that there were 26 million tons of such particles globally.
The researchers then analysed the geologic record, gathering data from ice cores, marine sediment records, and samples from peat bogs, which all highlight the layers of dust that had fallen from the sky. According to samples from around the globe, there has been a steady increase in desert dust.
Dust can increase as a result of drier soils, higher wind speed, and human land-use changes, such as diverting water for irrigation. Primarily, increases in dust levels due to that type of land-use changes have occurred on the borders of the world’s largest deserts, like the Sahara and Sahel in Africa and Asia’s Gobi desert, but similar changes have also taken place in California’s Owens Lake and are now occurring in the Salton Sea, also in California
The researchers argue that the factors that account for increased dust levels are not clear-cut or linear, and whether the amounts of desert particulates will increase, decrease, or remain relatively flat is unknown.
Climate models remain useful
While the increase in atmospheric dust has somewhat masked the full potential of greenhouse gases’ role in climate change, the findings do not show that climate models are wrong.
“The climate models are very useful in predicting future climate change, and this finding could further improve their usefulness,” Kok said.
