Atmospheric dust slowing greenhouse gas effect, for now
In our daily lives, dust is little more than a nuisance to be wiped away. On a global scale however, dust carried around the world on air currents has an impact on planetary temperatures. A new study shows that this dust could be masking the true impact of greenhouse gasses on climate change and that a shift in the dust quantity could lead to a sudden, albeit small, spike in worldwide temperatures.
Each year, millions of tons of dust is taken up from deserts around the world by our atmosphere. About 50% of this dust comes from the Sahara and Sahel Deserts, about 40% is from the Asian deserts, and the balance comes from deserts scattered about North America and the Southern Hemisphere. As the dust travels on atmospheric rivers and eventually drops back down to the ground, it has varying impacts on planetary temperatures.
For example, in the atmosphere, the dust can reflect light rays, helping to keep the planet cooler. The global dust cycle also keeps things cool by carrying nutrients like phosphorus and iron to the oceans, where they fuel the growth of phytoplankton, which act as a sink for carbon dioxide. On the ground though, dust can land on snow and ice, darkening it and making it heat up faster, which is a contributor to a warming planet.
According to researchers at the University of California, Los Angeles (UCLA), until now, dust's balance sheet has remained unsettled; it's never been clear if it has a net cooling or heating effect on global temps. To try to sort out its true climate impact, the researchers measured the amount of dust circulating around the planet using data from satellites and ground samples. They also took core samples from ice fields, peat bogs, and marine sediment for historical comparison points.
They found that the amount of dust in our atmosphere has been steadily increasing over time. In fact, the study carried out by the research team showed that the amount of desert dust circulating through the air is equal to 26 million tons, which is a 55% increase from the mid-1800s. This increase in airborne dust particles, the researchers say, has had a net cooling effect on global temperatures, masking up to 8% of the warming caused by greenhouse gasses.
This means that if the amount of dust in the atmosphere was to decline – an event that has repeatedly happened throughout history – temperatures could climb by about 0.1 degree Fahrenheit. That might not seem like such a big spike but, the researchers say, human activities have already warmed the planet by 2.2 degrees Fahrenheit so even one-tenth of one degree pushes us closer to the dangerously high increase of 2.7 degrees.
According to study's lead author, UCLA atmospheric physicist Jasper Kok, the true value in finally determining atmospheric dust's impact on planetary temperatures lies in factoring it – and its potential loss – into existing climate models.
"The increased dust hasn't caused a whole lot of cooling – the climate models are still close – but our findings imply that greenhouse gasses alone could cause even more climate warming than models currently predict," he 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 study has been published in the journal Nature Reviews Earth & Environment.