Desert dust masks true extent of climate change, research suggests

The full amount of warming caused by greenhouse gases has been hidden by microscopic airborne particles thrown into the air during desert dust storms, a new study suggests.

Furthermore, research by University of California, Los Angeles (UCLA) found that the amount of desert dust has grown roughly 55 per cent since the mid-1800s, which increased the dust’s cooling effect.

Some effects of atmospheric dust warm the planet, but because other effects of dust actually counteract warming – for example, by scattering sunlight back into space and dissipating high clouds that warm the planet – the study calculated that dust’s overall effect is a cooling one.

The researchers warn that if dust levels decline or stop growing, warming could ramp up.

“We show desert dust has increased and most likely slightly counteracted greenhouse warming, which is missing from current climate models,” said UCLA atmospheric physicist Jasper Kok, the study’s lead author. 

“The increased dust hasn’t caused a whole lot of cooling – the climate models are still close – but our findings imply that greenhouse gases alone could cause even more climate warming than models currently predict.”

While atmospheric desert dust levels have increased overall since pre-industrial times, the trend has not been steady and there have been upticks and declines along the way. 

As there are so many natural and human-influenced variables that can cause dust levels to increase or decrease, scientists cannot accurately project how the amounts of atmospheric dust will change in the coming decades.

Some of the microscopic airborne particles created by burning fossil fuels also temporarily contribute to cooling, but while scientists have spent decades determining the consequences of these human-made aerosols, the precise warming or cooling effect of desert dust remained unclear until now. 

Researchers faced challenges trying to determine the cumulative effect of the known warming and cooling effects of dust.

In addition to atmospheric interactions with sunlight and cloud cover, when dust drops back to earth it can darken snow and ice by settling on them, making them absorb more heat. 

Dust also cools the planet by depositing nutrients like iron and phosphorus. When those nutrients land in the ocean, for example, they support the growth of phytoplankton that take up carbon dioxide from the atmosphere, thereby causing a net cooling effect.

Human actions have so far warmed the planet by 1.2°C since about 1850. Without the increase in dust, climate change would likely have warmed the planet by roughly an additional 0.1°C.

“We want climate projections to be as accurate as possible and this dust increase could have masked up to 8 per cent 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.”

The researchers used satellite and ground measurements to quantify the current amount of microscopic mineral particles in the air. They determined that there were 26 million tons of such particles – equivalent to the weight of around five million African elephants floating in the sky.

They next looked at the geologic record, gathering data from ice cores, marine sediment records and samples from peat bogs, which all show the layers of atmospheric dust that had fallen from the sky. Samples from around the world showed 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 and turning marginal desert regions into grazing and agricultural land.