[There seems to be a lot of if-only-we-were-right-then-we-wouldn’t-have-been-wrong rationalization lately. Sam Harris’s latest covid rant comes to mind. ~cr]
UCLA researchers say climate change could accelerate slightly if dust levels stop rising
UNIVERSITY OF CALIFORNIA, LOS ANGELES
A new study shows that dust in the global atmosphere – microscopic airborne particles from desert dust storms – has a slight overall cooling effect on the planet, masking the full amount of warming caused by gases. greenhouse caused.
The UCLA study, published today in Nature Reviews Earth and Environmentfound that the amount of desert dust has increased by about 55% since the mid-1800s, which increases the cooling effect of the dust.
This study is the first to demonstrate the overall cooling effect of desert dust in the atmosphere. Some effects of dust in the atmosphere warm the planet, but other effects of dust actually counteract warming — for example, by scattering sunlight back into space and dissipating clouds. High clouds warm the planet — research has calculated that the overall effect of the dust is a cooling effect.
If dust levels decrease – or even simply stop growing – warming could increase, said Jasper Kok, UCLA atmospheric physicist and lead author of the study.
Kok, who studies how particulate matter affects climate, said: “We show that desert dust has increased and most likely has counteracted greenhouse warming, which is lacking in current climate models. “The increased dust doesn’t cause much cooling — climate models are still close — but our findings imply that greenhouse gases alone can cause more climate warming,” he said. than the models currently predict.
Kok compared this revelation to discovering that while driving a car at high speed, the vehicle’s emergency brake was partially engaged. Just as completely releasing the breaking force can make cars move faster, stopping dust levels from rising can slightly increase the rate of global warming.
And while levels of desert dust in the atmosphere have generally increased since pre-industrial times, the trend is volatile – there have been increases and decreases along the way. And because there are so many natural and man-made factors that can cause dust levels to rise or fall, scientists can’t predict exactly how the amount of dust in the atmosphere will change over the decades. next century.
Kok said some of the microscopic particles in the air created by burning fossil fuels also temporarily contribute to cooling. But while scientists have spent decades determining the consequences of these man-made aerosols, the exact warming or cooling effects of desert dust have so far been unclear. The challenge the researchers faced was determining the cumulative effects of the known heating and cooling effects of the dust.
In addition to atmospheric interactions with sunlight and cloud cover, when dust falls back to earth, it can darken snow and ice by depositing on them, causing them to 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 absorb carbon dioxide from the atmosphere, thereby causing a net cooling effect, Kok said.
Human action has warmed the planet by 1.2 degrees Celsius, or 2.2 degrees Fahrenheit, since about 1850. Had it not been for the increase in dust, climate change would have warmed the planet. add about 0.1 degrees Fahrenheit, Kok said. With the planet warming by nearly 2.7 degrees Fahrenheit that scientists consider particularly dangerous, every tenth of a degree matters, Kok said.
“We want climate projections to be as accurate as possible, and this dust increase could mask up to 8% of greenhouse warming,” said Kok. “By adding in an increase in desert dust, which makes up more than half of the mass of particulate matter in the atmosphere, we can increase the accuracy of climate model predictions. This is extremely important because better predictions can lead to better decisions about how to mitigate or adapt to climate change.”
The researchers used satellite and ground measurements to quantify the amount of microscopic mineral particles present in the air. They determined that there are 26 million tons of such seeds globally — equivalent to the weight of about 5 million African elephants floating in the sky.
Next, they reviewed the geological record, collected data from ice cores, marine sediment records, and samples from peat bogs, all of which showed layers of atmospheric dust falling from the sky. Samples from around the world show a steady increase in desert dust.
Dust can be increased by drier soils, higher wind speeds, and changes in human land use — such as diverting water for irrigation and turning marginal deserts into grazing land and agricultural land. Although dust levels rise due to those kinds of land-use changes mainly occur at the borders of the world’s largest deserts, such as the Sahara and Sahel in Africa and the Gobi desert of Asia, Kok said. , similar changes took place in the Owens of California Lake and are now occurring in the Salton Sea, also in California.
But the factors that cause dust levels to rise are not clear or linear, Kok said, and whether the amount of desert particles will increase, decrease or remain relatively flat is unknown.
Kok stressed that although an increase in atmospheric dust has somewhat obscured the full potential of greenhouse gases in warming the climate, the findings do not suggest that the climate models are wrong.
“Climate models are very useful in predicting future climate change, and this finding could further improve their usefulness,” said Kok.
MAGAZINE
Nature Reviews Earth & Environment
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