Investigating the causes behind the differences necessary for more accurate results, say experts
There were differences in the aerosol concentrations in the atmosphere as measured by ground observations and climate models, according to a new study. The variation in the findings may have a bearing on climate policymaking.
Aerosols are tiny particles or droplets that float in the air and influence climate.
Both climate models and ground measurements showed that aerosol concentrations are on a decline. But the relative average decrease was lower according to the models than in the ground measurement, the paper published in Atmospheric Chemistry and Physics noted.
“For seasonal trends in general, the differences were larger,” the experts wrote in the study.
The report also found that the results from the five climate models varied, despite being fed with the same data on anthropogenic mass emissions.
“There were differences in the seasonal pattern, magnitude and when the maxima of number concentrations were achieved,” they added.
The sources of aerosols are erupting volcanoes, sea salt and wildfires. Humans, too, add aerosols to the atmosphere by burning fossil fuels such as coal, oil and gas, according to the University Corporation for Atmospheric Research, a non-profit.
Aerosols can damage lung tissue and lead to lung diseases. They also influence the climate by changing how much solar energy is absorbed or reflected away from Earth, it added.
The authors of the study explained that climate models need to capture the distribution and characteristics of the atmospheric aerosol population to better predict the amount of warming or cooling they can produce. This, they said, would improve the estimate of climate sensitivity and future climate change.
Researchers from multiple European institutes compared aerosol concentration trends and seasonality between climate models and measured figures.
They utilised long-term time series data from 21 observation sites and results from five different climate models.
Measured results showed that the number concentrations of particles were usually higher at urban sites and in southern and central Europe than in rural areas in northern Europe. This was in line with previous studies, the experts explained.
Seasonal variation is modelled differently in different projections, the research paper highlighted.
Some models describe seasonal variations similarly regardless of the location of the observation site, while others consider changes in the North-South axis, it added.
“It is notable that the greatest differences were found in particle size, which plays a key role in the cloud formation process,” the researchers said.
Aerosols influence the Earth’s climate by acting as seeds on which clouds form, the United States Department of Energy explained.
Increased aerosol particles can lead to more but smaller cloud droplets, which may likely reduce rains that fall from the cloud, it added.
The differences between climate models recorded in the study could be due to how they describe the formation, development and transport of aerosols, according to the paper.
The researchers recommend that a more detailed characterisation of processes causing model differences needs to be carried out in the future. This could help understand the essential reasons for the differences observed in the models, they said.
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