Last week, many Spaniards woke up to find dust covering their balconies, streets, and cars. The visibility in the capital city, Madrid, reduced to 2.5 miles. By the middle of the week, the dust reached as far as Central Europe and by the end of the week to Northern Europe.
Storm Celia brought dust from the Sahara Desert to southern parts of Spain, also affecting Madrid. On Monday, 14th March, PM2.5 was 10.2 μg/m3 in Madrid. On Tuesday, 73.1 μg/m3 (Unhealthy), and by Wednesday, it came down to 30 μg/m3 (moderate). The national air quality index listed the air quality of Madrid as “extremely unfavorable”.
Fine particles with a diameter of less than 10 μm (PM10) are not only hazardous to the environment, but also to human health. In humans, it can be carried deep into the lungs, causing inflammation and exacerbating heart and lung problems. Although in 2019, the premature deaths from air pollution decreased by 33%, compared to 2005, the EU still recorded approx. 307,000 premature deaths from fine particulate matter; 40,400 due to nitrogen dioxide exposure, and 16,800 from acute ozone exposure.
The annual mean concentration of fine particles (PM2.5) in urban areas of the EU was 12.6 μg/m3 in 2019, which was still above the recommendation threshold by the World Health Organization (10 μg/m3 annual mean). As a result, the EU adopted the Zero Pollution Action Plan in 2021 to reduce the number by 55% by 2030, compared to 2005.
The dust pollution that occurred by storm Celia has hinted that meeting the zero-pollution action target would be difficult, as we cannot directly control the storm. Although experts are still unclear if climate change had a direct link to the storm, the expansion of the Sahara Desert over the past century has increased the potential for larger dust storms in Europe.
Expansion of the Sahara desert
During the 1970s-1980s, West Africa experienced severe drought, resulting in land degradation and desert expansion. It directly affected the countries, such as Sudan, Chad, Mauritania, and Libya. One paper reported that the desert advanced approx. 100 km southward in 1950–2015. In 2015, Reuters reported that the Sahara desert is expanding southward at a rate of 48 km a year, forcing whole communities to migrate.
Researchers warn that the expansion of the desert is more frightening than the storm flying dust from it. As the desert has been expanding unannounced for many decades, the end effect could be much worse than what we are seeing now. A report published in the Journal of Climate stated that two-thirds of the desert’s growth is a result of natural climate cycles, while the remaining one-third from climate change.
How does climate change expand the Sahara desert?
It was not the first time a storm has swept away dust from the Sahara. In summer 2020, the Storm Godzilla swept nearly 24 tons of dust from the desert to North and South America. Beginning of March 2022, dust traveled across Cape Verde on its way over the Atlantic to the Caribbean and South America. These are just a few examples.
The expansion of the Sahara Desert could be due to the widening of Hadley circulation, which is likely caused by climate change. The research team at the University of Maryland studied the expansion of the desert and suggested that the natural climate cycle called the Atlantic Multidecadal Oscillation (AMO), in which temperatures over the northern Atlantic Ocean fluctuated between warm and cold phases for more than 50 years, could be the reason.
The team studied grids and patterns from 1920 to 2013 and determined, that from the 1930s to the early 1960s, the AMO was in a positive phase (warm) that initiated more rain to areas near the Sahara. It then switched to a negative cycle (cold) for the next 40 years. The later phase resulted in a drought during the 1980s and throughout this time, the Sahara Desert crawled towards the south.
Is the storm the result of climate change?
The course of hot summers getting hotter and drying out of rainy seasons in Africa are attributed to the increase of greenhouse gases. The increase of global surface temperatures results in more heat in the atmosphere, which increases ocean surface temperatures. This increases wind speeds in tropical storms.
A team led by JPL’s Hartmut Aumann, Atmospheric Infrared Sounder (AIRS) project scientist, analyzed 15 years of AIRS data between 1993 and 2012, looking for correlations between average Sea Surface Temperatures and the formation of extreme storms. They found that extreme storms formed when Sea Surface Temperatures were hotter than 28 °C, and for every 1 °C that Sea Surface Temperature increased, the number of extreme storms went up by about 21%.
If we do not meet the target of net-zero on time, scientists predict that the result of climate change will be even more intense Saharan dust storms in the future.
