Tuesday, March 28

Is climate change behind the new haze episode in the Canary Islands?

In the air we breathe there are always small particles of dust, ash or soot of different sizes. They are not in the atmosphere for one reason only. There are purely natural factors, such as forest fires or volcanic eruptions, that cause their presence. And there are other anthropogenic causes, such as agricultural work or construction, that too.

The impressive calima storm over the Canary Islands becomes the image of the Copernicus week

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They are usually not very big. There is a classification for the smallest, those that measure less than 2.5 microns (PM2.5); and there are those smaller than ten microns (PM10), which work very well to measure the air quality of an area. If the daily average of PM 10 exceeds 50 μg/m³, the threshold set by both the European Union and the World Health Organization (WHO) would be exceeded, and could begin to be dangerous for the health of the most vulnerable people.

When the haze reaches the Canary Islands, there is a rare day that this limit is not exceeded. In January of this year it has occurred up to twelve days in many of the air quality measurement stations, according to data provided by the Control and Surveillance Network. The last time something similar happened was during the historic Saharan dust intrusion episode that the Archipelago suffered in February 2020, just before the coronavirus lockdown.

That chapter was thoroughly studied by the scientists of the Islands. The concentrations of PM10 and PM2.5 exceeded 3,000 and 1,000 micrograms per cubic meter, causing the Archipelago to have at that time the worst air quality in the world and the most harmful recorded in its history. All the airports on the islands were closed due to lack of visibility, something that had never happened before.

On this occasion, it is clear that the magnitude of the phenomenon (at least in economic terms) has not been the same, but having experienced another such important event of Saharan dust intrusion has once again brought to the table a question that is so easy to formulate and difficult to answer: is climate change behind all this? The scientific literature on this is not conclusive. Much more evidence and causal relationships are needed to indicate this.

Because so far everything is a bit confusing. “The more I study about this, the more I doubt it,” reflects Emilio Cuevas, director of the Izaña (Tenerife) Atmospheric Research Center of the State Meteorological Agency (AEMET). According to a thesis signed in 2007 by Silvia Alonso Pérez, professor and researcher at the University of La Laguna (ULL), and directed by Cuevas himself, since the 1970s there has been an increase in both the frequency and intensity of episodes of African dust.

Along with this, an increase in air temperature, a decrease in specific and relative humidity and a weakening of the trade winds have also been observed. “It seems, therefore, that the beginning of the trend (…) coincides with the beginning of the indication of climate change,” the expert concludes. However, not all studies reach the same conclusion.

Another article, this time published in the magazine Atmospheric Measurement Techniques in 2015, using artificial intelligence techniques, it reconstructs the amount of dust that there has been in Tenerife from the 1940s until now, analyzing the evolution of associated parameters, such as wind direction or visibility.

According to that document, in the 1940s and 1950s there were more days with Saharan dust intrusions than now. “What this generates for us is enormous uncertainty about the assessment that can be made of the haze and climate change. We must be very cautious and not extrapolate a small trend to the rest of reality,” adds Cuevas.

The issue is much more complex than it seems. There is no long-term data series that unequivocally shows what is happening. We have so much evidence of climate change because it is right at the beginning of the Industrial Revolution, with the massive use of coal, when the average annual temperature of the planet has been increasing. But to investigate the haze or the intrusions of African dust there are no such long series (even remotely).

In 2005, a group of researchers from the Canary Islands studied the frequency, seasonality and trends of advections of African air in the Canary Islands between 1976 and 2003. They concluded that on average there have been 14 each year, that winter is the season in which they occur the most and that its duration can vary from 15 days to four. But as to whether or not they have increased, no noticeable change seen. In any case, it is the other way around. “A maximum is observed in the early 1980s and a slight decrease in recent years, but the series does not indicate a clear trend.”

In fact, this coincides with work being carried out these days at the AEMET research centers on the Islands. Canary airports detail every day the reduction in visibility due to dust. If we take from the first available figure, in the 80s, until now, “there is even a decrease in episodes,” says Cuevas. “We are aware that climate change exists. But, although it seems obvious from human perception that further warming of the Sahara causes more dust intrusions, it turns out that this is not the case.”

And Cuevas argues: “Depending on the period we are looking at, we can get surprises with the dust. In the 80s there were more episodes than now and in general they were more intense. The one in 2020 may be the biggest, but four decades ago more were produced. Then, if we look at other estimates, there are also striking facts. A study by the Complutense University of Madrid (UCM) found that the arrival of Saharan dust in the Iberian Peninsula has increased by 400% in the last five thousand years.

The possibility that the haze continues the same path that, predictably, the tropical storms in the Mediterranean will follow is not ruled out. That is, they are less frequent episodes, but more intense. Because what is unquestionable is that aridification is taking place in North Africa and, due to this desertification, there is more and more dust. In 2020, the record for concentrations of dust in suspension from deserts was reached, according to the latest analysis of the World Meteorological Organization (WMO). Another thing is that the wind carries these particles to the Canary Islands.

“We know that the warming of North Africa and the Sahara will mean changes in dust transport patterns, but we don’t know how yet. There will be areas with more dust and others with less. Canaries? We don’t know. We don’t have details of how future developments will be,” explains Cuevas.

What we do know is that, in 2020, the last year studied, in the south of Gran Canaria, the daily PM10 threshold was exceeded for up to 111 days, almost always due to the arrival of haze. We also know that this information is ambivalent: for the governments it says little about their actions, because they have nothing to do against intrusions of Saharan dust (what is more, the data that is usually offered on air quality does not take into account the phenomena natural); but for health it is a problem.

The risk that the haze poses, especially for vulnerable people and those with respiratory problems, is already more than proven. A study led by the Cardiology Service of the Hospital Universitario de Canarias concluded that the risk of cardiovascular death increases by 2% on the same day of exposure to these phenomena.

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