and alter studies on heat-

Aerosol, that set of suspended particles in the air that filters solar radiation, can contribute to climate change: depending on the level of concentration of these particles, it can slow down to almost block the solar radiation in the balloon. It is another element of the cocktail that – with the first ingredient being the increase in CO2 and greenhouse gases in general – contributes to triggering climate change and the ongoing global warming. And an element of uncertainty because it alters the results of studies on greenhouse gases making forecasts less reliable: as early as 2011 a study by the University of Michigan had shown that projections of the effects of aerosols on the climate of Earth from satellite data are at risk of underestimation. they. significantly impact.

Today, aerosols are at the heart of a new series of in-depth studies in the field of research aimed at dispelling the uncertainties inherent in their relationship with other climate-altering gases. Planet 2030 spoke with Paolo Laj, a researcher at the University of Grenoble and an expert on the subject, on the occasion of the PM2022 conference, which took place in Bologna three weeks ago.

Why is aerosol so important when it comes to climate change?
The aerosol is made up of very small particles, which remain suspended in the air and reflect solar radiation. Thus, when there are particles in the air, there is less solar radiation reaching the ground and the weather tends to cool. When there is a volcanic eruption, the ash suspended in the air creates this effect and it is known that the temperatures of the year following the event will tend to be lower.

What are the climatic certainties and uncertainties in the field of aerosols?
We know that the spray cools the climate on average. Cooling due to aerosols is much less than heating due to greenhouse gases, so it goes the other way but has less impact. There is a lot of uncertainty about the lesser the cooling effect. The effect of greenhouse gases is much more widespread, it works day and night and the same everywhere. The effect of aerosols, on the other hand, only occurs during the day and varies from place to place. it is precisely this local specificity that makes the sphere of aerosols very uncertain, because the very small scale in which they act escapes the more general description of the phenomena, which in turn is found in models. One of the most uncertain processes is the relationship between particle aerosols and clouds, that is, how much clouds change when there are more or less particles. When it comes to making a climate forecast, the generalization of the models means that we cannot predict everything in detail. What is called parameterization is needed, that is, the simplification of processes.

What aspects and evidence of aerosols did the latest IPCC Physical Bases Report, published last year, highlight?
The latest report stressed that there is no longer any doubt that climate change is taking place, in fact it is measurable. There is no longer any doubt that this is determined by carbon dioxide emissions from human activities. There are uncertainties about the role of each of the atmospheric components, that is, how much the particles heat and cool the atmosphere. The report showed that, despite the uncertainties we have mentioned, the only way forward for companies to remain is to reduce carbon dioxide emissions.

So, in your opinion, do governments make the right decisions in this regard?
Undoubtedly, decisions on climate policy must be made absolutely as soon as possible. The priority is obviously to reduce CO2 emissions, but decisions must also be made to reduce both greenhouse gases and the particles or precursors of these particles. If we look at the Po Valley, which has always been one of the most polluted areas in Europe, but air quality policies have worked and the situation has improved. These policies have clearly acted on air pollutants. We now need to act more specifically on carbon dioxide emissions and this will lead to a change in our lifestyle. The only thing we have not been able to act on is ozone concentrations, which will also increase in proportion to global warming.

Why are ozone levels important?
Ozone is formed in summer by the sun’s rays, which interfere with nitrogen and volatile organic compounds. As the climate becomes warmer in the future, so will ozone concentrations. To limit ozone formation, it is necessary to act on its nitrogen precursors and volatile organic compounds, which are emitted mainly by car traffic and certain industrial processes. We have been able to do a lot in terms of air quality, but there is still a long way to go. It can only be done by changing things drastically and not blindly relying on technologies, which can help us but not just the solution. Just an example: to reduce road traffic emissions by three orders of magnitude, it would be enough for the car to carry four people instead of one. (ed. car pooling), while it would take ten years to achieve the same goal with technology.

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