Atmospheric physicist Jasper Kok is an associate professor in the Department of Atmospheric and Marine Sciences at the University of California, Los Angeles (UCLA). In an interview with MIT Technology Review, he talks about his new study on dust in the earth’s atmosphere – and the question of what climate effects it has – or had.
Professor Kok, you and your team have discovered that dust in the atmosphere has apparently protected us from even more serious effects of global warming. How did you come to this realization?
Jasper Kok is an atmospheric physicist at UCLA.
It has long been known that such particles have a cooling effect in the atmosphere because they deflect sunlight as part of the greenhouse effect. But we didn’t know exactly what the balance was, i.e. whether it really had a mitigating effect on climate change. We have now calculated this and, based on current knowledge, conclude that this has most likely cooled the climate system as a whole. To do this, we calculated all possible effects of dust on the climate system. And there are very many. For example, desert dust scatters light back into space, which cools it down, but it also affects things like cloud formation in a number of different complex ways. Conversely, it serves as a sink for anthropogenic pollution such as sulfates and nitrates in the atmosphere, which would otherwise produce particles and have a cooling effect. Here again the heat potential increases.
They have also investigated how the dust concentration changes. So far it has increased.
You can see this in ice cores, for example, if you drill into the ice and find different dust concentrations in different ice layers that correspond to different years. From about 20 of these different measurements around the world, we found that most of them show that dust has increased over time.
From this we conclude that various major natural dust-producing areas such as North Africa, the Sahara Desert, the Gobi Desert, the deserts of Central Asia and the Americas have been shedding more particles since about the mid-19th century, about 50 to 60 percent more. So this cooling effect has increased. And that has partially offset warming from greenhouse gases.
“Desert dust is one of these types of aerosols”
What happens there?
In general, global warming is a battle between the greenhouse gases that warm the planet and aerosols. Particulate matter is therefore cooling the planet. Desert dust is one of these types of aerosols. And then there is a whole range of aerosols that are produced by humans. These are in particular sulphate aerosols, which are produced when fossil fuels are burned.
What is the cooling effect?
We calculated that this could have offset about a third of the warming from the greenhouse effect. About 10 percent of that third is due to increases in natural dust like that from the desert, but the other 90 percent comes from substances like sulfates that have increased due to human activity.
But over time, air pollution has decreased, which has also led to a decrease in aerosol concentration?
Sulfates peaked around the year 2000. So the cooling, the protection that we had from these aerosols is gone. And that may be one of the reasons the climate has been warming so quickly over the last few decades – faster than it used to.
You also noticed a decrease in desert dust after it had been increasing since the mid-19th century.
This atmospheric dust appears to have peaked in the 1980s and has been declining ever since. We don’t yet know why this is so.
“Dust is really complicated”
To what extent is atmospheric dust already part of current climate models?
Almost all climate models include it, but dust is really complicated. It depends on the drought, it depends on the plants, it depends on the winds and the meteorology. None of the climate models that we know of have been able to reproduce the increase in atmospheric dust that we have observed. And that has apparently masked the warming from greenhouse gases.
Of course, one could now argue: Let’s pollute more, then there will be more particles in the atmosphere again and it will cool down more.
It is true that this “protection” from even more warming that we have received from man-made pollution is waning. Global warming is accelerating. And there are indeed suggestions that if warming reaches a particularly dangerous level – say exceeds the 1.5 or 2 degrees of the Paris climate agreement – then one could try to technically cool the planet. This includes the idea of, for example, introducing aerosols into the stratosphere, high up in the atmosphere. Of course nobody wants that. But the world could be moving in a direction where this discussion is becoming more and more relevant.
Geoengineering as a last resort
What would that look like?
The particles would be used high in the atmosphere – about 20 kilometers – to cool the planet, where they don’t have much of an impact on human health. That would be possible with balloons or very high-flying aircraft. The exact technical details have yet to be worked out, but there are various proposals for this. But it is already clear that this would have many other negative effects, e.g. B. the influencing of precipitation patterns, i.e. where and how much it rains. And it raises all sorts of difficult geopolitical questions. So that would only be a last resort. In English we would call this a “Hail Mary Pass”.
What are the next steps now that we have your study?
The task now is to ensure that these findings are reflected in the climate models. So that we incorporate this knowledge of dust and its cooling effects into it so that we can get even more accurate predictions of how much warming we’re getting. We are already talking to the developers of such models and are organizing a large modeling experiment.
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