NEW DELHI :
Nearly five weeks of lockdown has not only brought down pollution levels to unprecedented levels in the country, it has also possibly influenced the local weather – an impact which the atmospheric scientists are now attempting to investigate.
According to National Aeronautics and Space Administration (NASA), the aerosol concentration has gone down drastically over North India bringing clear skies after decades. The impact is more evident over the Indo-Gangetic region- one of the most polluted and densely populated regions in the world.
Aerosols are particles in the atmosphere around which water droplets tend to condense and form clouds. But, their role is not just limited to cloud formation; these particles also absorb and reflect the sunlight in the atmosphere depending on their composition.
“It appears that recent reduction in the pollution levels could contribute to an increase in local temperatures. It is largely because there is reduction in aerosols that can absorb more solar radiation," said Roxy Mathew Koll, climate scientist from Indian Institute of Tropical Meteorology (IITM), Pune.
But it is not simple, as these aerosols are of several types and their chemical composition differs, which makes it difficult to quantify their role in climate system. Also, scientists highlight that the emerging effect of aerosol warming (if any) could be offset by the cooler than normal temperatures that persisted over north India from January to March this year.
But if the current state of reduced pollution levels due to lockdown continues into May and warming persists, there is probability that it could exert some influence the southwest monsoon which is set to make its onset over the Indian coast in early June.
“If we take the general theory of monsoon, increased warming over land would pull the monsoon current from the oceans. So, an increase in surface warming because of reduction of aerosols could enhance the early part of the southwest monsoon. But we do not know, if this would happen, until we actually quantify the role of aerosols in our climate models," said Vinoj V, scientist from Indian Institute of Technology (IIT), Bhubhaneshwar.
The southwest monsoon sets in over India in early June, when there is a huge warming on the mainland creating a low pressure system, pulling the monsoon-laden winds from the cooler Indian Ocean, which driving the monsoon circulation.
The probable scenario indicates the monsoon rains could be better, but scientists are yet to test this using weather models. Meanwhile, the India Meteorological Department (IMD) too has predicted the monsoon to be normal this year in its first long range forecast, with a 21 % probability of excess rains.
“There can be some impact on the local weather because of falling aerosol concentration at regional levels. But to see a direct, large-scale monsoon impact, we will have to wait and see," said D S Pai, senior scientist at India Meteorological Department (IMD), Pune.
Since the weather is dynamic, meteorologists highlight any effect from reduced pollution during this lockdown is difficult to predict, but could most-likely short-term, unless the lockdown continues for next few months.
Though, there may be no new addition of greenhouse gases into the atmosphere, but the ones being emitted for last several decades continue to remain. Compared to aerosols which have a short lifetime of not more than two weeks, carbon dioxide gas has a lifetime of several hundred years.
“There is fall in new emissions globally because of the lockdown and if it continues, we can expect slight cooling after several months. But, it may not be noticeable, as there are other natural meteorological factors also at play. A substantial impact can be seen only is these changes last for months and years," added Pai.